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10 ton asteroid impact	has average interval time 1 year
	is a kind of asteroid impact
100 ton asteroid impact	has average interval time 10 years
	is a kind of asteroid impact
1000 ton asteroid impact	has average interval time 100 years
	is a kind of asteroid impact
16th century scientist	has definition a scientist born between 1500 and 1600 AD
	is a kind of dead person
	is a kind of scientist
17 Leporis	has companion M1 III
	has definition A close binary system (A0 V, M1 III) with a shell-like spectrum indicating that mass transfer may be occurring from the late-type companion onto the A0 primary.
	has primary A0 V
	is a part of Lepus
	is an instance of binary star
	is an instance of shell star
17th century scientist	has definition a scientist born between 1600 and 1700 AD
	is a kind of dead person
	is a kind of scientist
18th century scientist	has definition a scientist born between 1700 and 1800 AD
	is a kind of dead person
	is a kind of scientist
19th century scientist	has definition a scientist born between 1800 and 1900 AD
	is a kind of dead person
	is a kind of scientist
2-meter Telescope	has altitude 331 m
	has aperture 1.34 m
	has comment can also be used in Cassegrain and coude modes
	has creation date 1960
	has focal ratio f/3.00
	has has mirror diameter 2 m
	has latitude 50° 59' N
	has location Tautenberg, Germany
	has longitude 11° 43'E
	has mirror maker Zeiss (Jena)
	has mirror type Schott ZK-7 glass
	has mounting manufacturer Zeiss (Jena)
	has owner Karl Schwarzschild Observatorium
	has synonym Tautenberg Schmidt
	is an instance of Fork equatorial telescope
	is an instance of Schmidt
2.3-meter Telescope	has altitude 725 m
	has aperture 2.33 m
	has creation date 1985
	has focal ratio f/3.25, 13, 43
	has latitude 12° 35' N
	has location Kavalur, Tamil Nadu, India
	has longitude 78° 50' E
	has mirror maker Indian Inst. Astrophys.
	has mirror type Zerodur
	has mounting manufacturer Walchandnagar Industries
	has owner Vainu Bappu Observatory
	has synonym Vainu Bappu 2.3 m
	is an instance of Horseshoe equatorial telescope
	is an instance of optical telescope
	is an instance of reflector
20th century scientist	has definition a scientist born between 1900 and 2000 AD
	is a kind of scientist
26-inch Equatorial	has altitude 92 m
	has aperture 0.66 m
	has creation date 1873
	has focal ratio f/15.0
	has latitude 38° 55' N
	has lens maker Alvan Clark & Sons
	has location Washington, DC, US
	has longitude 77° 04' W
	has mounting manufacturer Warner and Swasey
	has owner US Naval Observatory
	is an instance of German equatorial telescope
	is an instance of refractor
28-inch Visual Refractor	has altitude 47 m
	has aperture 0.711 m
	has comment Dome under repair in 1992
	has creation date 1894
	has focal ratio f/11.9
	has latitude 51° 29' N
	has lens maker Gmbh
	has location Greenwich, London, England
	has longitude 00° 00'
	has mounting manufacturer Ransomes and Sims
	has owner Old Royal Observatory
	has synonym Greenwich refractor
	is an instance of English equatorial telescope
	is an instance of refractor
2U 1543-47	is an instance of transient X-ray source
3 alpha process	has definition A nuclear reaction (3 4He → 12C + γ + 7 MeV) by which helium is transformed into carbon. The process is dominant in red giants. At a temperature of about 2 × 108 K and a density of 105 g cm-3, after core hydrogen is exhausted, three α-particles can fuse to form an excited nucleus of carbon 12, which occasionally decays into a stable carbon 12 nucleus. The overall process can be looked upon as an equilibrium between three helium nuclei and the excited 12C*, with occasional irreversible leakage out of the equilibrium into the ground state of carbon 12. Further capture of α-particles by carbon 12 nuclei produces oxygen 16 and neon 20. (also called the triple-α process)
	is a kind of nucleosynthetic reaction
3-kpc arm	has definition A component of the Sagittarius arm with noncircular gas motions. It is seen in absorption against Sgr A with a velocity of -53 km s-1, implying that at least part of the arm is expanding away from the galactic center. The nearest "edge" is presently at a radius of 4 kpc from the Galactic center.
	is a part of Sagittarius arm
3.5-meter Telescope	has altitude 2168 m
	has aperture 3.50 m
	has creation date 1984
	has focal ratio f/3.5, 3.9, 10, 35
	has latitude 37° 13' N
	has location Calar Alto, Spain
	has longitude 2° 32' W
	has mirror maker Zeiss (Ober.)
	has mirror type Zerodur
	has mounting manufacturer Voith, Heidenheim; Zeiss (Ober.)
	has operator German-Spanish Astronomical Center
	has owner Calar Alto Observatory
	is an instance of Horseshoe equatorial telescope
	is an instance of optical telescope
	is an instance of Ritchey-Chrétien
30 Doradus Nebula	has absolute magnitude Mv = - 19
	has definition A giant H II region, at least 300 pc across - one of the largest known. It is larger and more luminous than any known in the Galaxy. It is the brightest object in the Large Magellanic Cloud at both optical and radio wavelengths, and contains the densest concentration of W-R stars. (The brightest object near the center is a O+ WN star of Mv = - 10.2.) It is characterized by very rapid, disordered, and complex motions.
	has distance 170000 light years
	has image
	has synonym Great Looped Nebula
	has synonym NGC 2070
	has synonym Tarantula Nebula
	is a part of Large Magellanic Cloud
	is an instance of gaseous nebula
36-inch Refractor	has altitude 1290 m
	has aperture 0.895 m
	has comment Front surface of crown element refigured in 1987
	has creation date 1888
	has focal ratio f/19.7
	has latitude 37° 20' N
	has lens maker Alvan Clark & Sons
	has location Mount Hamilton, Calif., US
	has longitude 121° 39' W
	has mounting manufacturer Warner and Swasey
	has owner Lick Observatory
	has synonym 36 inch
	is an instance of German equatorial telescope
	is an instance of refractor
3TA-10 Schmidt Telescope	has altitude 1450 m
	has aperture 1.00 m
	has comment three 1 m diameter objective prisms
	has creation date 1961
	has focal ratio f/2.13
	has latitude 40° 20' N
	has location Mount Aragatz, Armenia
	has longitude 44° 30' E
	has mirror diameter 1.5 m
	has mirror maker LOMO
	has mounting manufacturer LOMO
	has owner Byurakan Astrophysical Observatory
	has synonym Byurakan Schmidt
	is an instance of Schmidt
4-kpc arm	has definition A component of the Sagittarius arm with noncircular gas motions.
	is a part of Sagittarius arm
40 Eridani	has definition A nearby triple system, 5 pc distant. Component A is K0 V; component B is a DA white dwarf; component C is M5e V.
	is a part of Eridanus
	is an instance of triple star
47 Tucanae	has definition A metal-rich globular cluster. It has roughly one-quarter the solar metal abundance. It has a high galactic latitude and low reddening. It is a member of the thick-disk population.
	has distance 15000 light years
	has image
	is a part of halo
	is a part of Tucana
	is an instance of unclassified globular cluster
4N nucleus	has definition Nuclei possessing equal and even numbers of neutrons and protons. 4N nuclei are formed in supernova envelopes at temperatures of at least 2 × 109 K and are very stable.
	has synonym even-even nucleus
	is a kind of Bose-Einstein nucleus
53 Arietis	has definition Runaway star which diverges from a comparatively small area in Orion.
	is a part of Aries
	is an instance of runaway star
61 Cygni	has definition The first star other than the Sun to have its parallax, and hence distance, measured. The star is a double orange dwarf.
	has distance 11.4 light-years
	is a part of Cygnus
	is an instance of high proper motion star
[O III] line	is a kind of forbidden line
[WR] star	has definition WR star that is the central object of a planetary nebula.
	is a kind of Wolf-Rayet
A band	has definition One of about a dozen of the strongest Fraunhofer lines seen in the Solar spectrum, the A band at 7600 angstoms is due to telluric lines of molecular oxygen in the Earth's atmosphere. (originally thought to originate in the Sun by Fraunhofer)
	has species O2
	has wavelength 7600 Å
	is a kind of Fraunhofer line
	is a kind of molecular band
	occurs in Earth's atmosphere
A ring	is a kind of ring
	is a part of Saturn ring system
A star	has absorption line H I
	has color white
	has definition Star with spectral type A in which the spectrum of the Balmer lines of hydrogen attain their greatest strength. Helium lines can no longer be seen. Some metallic lines are present; in late A stars the H and K lines of ionized calcium appear. A0 stars have a color index of zero.
	has surface temperature 10000 K
	is a kind of early star
ablation	has definition Removal of material from a solid by heating, vaporization or collisions
	has example Erosion of a meteorite by the friction generated when it passes through the Earth's atmosphere. The material passes from solid to gas phase.
	has final phase gas
	has initial phase solid
	has inverse process condensation
	is a kind of first order phase transition
absolute magnitude	has definition A measure of the intrinsic brightness of a star or galaxy. Absolute magnitude is defined as the apparent magnitude the star or galaxy would have if it were 32.6 light-years (10 parsecs) from Earth. The lower an object's absolute magnitude, the greater its intrinsic brightness. For example, the Sun has an absolute magnitude of +4.83, while Sirius, whose intrinsic brightness is greater, has an absolute magnitude of +1.43. A star that is one absolute magnitude brighter than another (e.g., +4 versus +5) is 2.5 times intrinsically brighter; a star that is 5 absolute magnitudes brighter is 100 times intrinsically brighter; and a star that is 10 absolute magnitudes brighter is 10000 times intrinsically brighter.
	has definition The absolute magnitude (g) of a solar-system body such as an asteroid is defined as the brightness at zero phase angle when the object is 1 AU from the Sun and 1 AU from the observer.
	is a kind of magnitude
absolute temperature	has definition Temperature measured on the Kelvin scale: 0 Kelvin = -273.15 ° Celsius. Absolute temperature is directly related to (kinetic) energy via the equation E = kBT, where kB is Boltzmann's constant. So, a temperature of 0 K corresponds to zero energy, and room temperature, 300 K = 27 °C, corresponds to an energy of 0.025 eV.
	is a kind of temperature
absolute zero	has definition The lowest possible temperature, attained when a system is at its minimum possible energy. The Kelvin temperature scale sets its zero point at absolute zero (-273.15° on the Celsius scale, and -434.07° on the Fahrenheit scale).
	is an instance of temperature
absorption	has definition Decrease in the intensity of radiation, representing energy converted into excitation or ionization of electrons in the region through which the radiation travels. As contrasted with monochromatic scattering (in which reemission occurs in all directions at the same frequency), the inverse process of emission refers to radiation that is reemitted in general in all directions and at all frequencies.
	has inverse process emission
	is a kind of radiation intensity modification
absorption edge	has definition Sudden rises superposed on the smooth decrease of the curve of the attenuation coefficient, which cause the curve to have a typical sawtooth aspect. They generally occur at the limit of spectral lines.
	is a kind of spectral feature
absorption line	has antonym emission line
	has definition Dark line in a spectrum, produced when light or other electromagnetic radiation coming from a distant source passes through a gas cloud or similar object closer to the observer. Like emission lines, absorption lines betray the chemical composition and velocity of the material that produces them.
	has definition Dark line superposed on a continuous spectrum, caused by the absorption of light passing through a gas of lower temperature than the continuum light source.
	is a kind of spectral line
abstraction	has definition a general concept formed by extracting common features from specific examples
	is a kind of kbTop
acceleration unit	has definition meter per second squared
	has symbol m·s-2
	is a kind of derived SI unit
accretion	has definition A process by which a star accumulates matter as it moves through a dense cloud of interstellar gas; or, more generally, whereby matter surrounding a star flows toward it (as in close binaries).
	has definition Collection of material together, generally to form a single body.
	is a kind of contraction
accumulating oceanic element	has ocean concentration depth indenpendent
	has ocean residence time 105 years or greater
	is a kind of oceanic element
accumulation theory	has definition The theory by which planetesimals are assumed to collide with one another and coalesce, eventually sweeping up enough material to form the planets.
	is a kind of planetary theory
acetaldehyde	has symbol CH3CHO
	is an instance of interstellar molecule
Achernar	has B-V magnitude -0.16
	has declination -57 14 12
	has distance 35 pc
	has right ascension 1 37 42.9
	has spectral type B3Vpe
	has spectral type B5
	has synonym alpha Eridani
	has synonym HR 472
	has V magnitude 0.46
	is a part of Eridanus
	is an instance of B star
	is an instance of naked eye star
	is an instance of subgiant
Achilles	has asteroid number 588
	has definition Trojan asteroid (60°) ahead of Jupiter. It was the first Trojan to be discovered.
	has discovery date 1906
	has eccentricity e = 0.15
	has inclination i = 10°.3
	has orbital period P = 11.98 yr
	has semi-major axis a = 5.2 AU
	is a part of Trojan asteroid
	is an instance of Trojan asteroid
achromatic lens	has definition Lens (or combination of lenses) that brings different wavelenghts within a ray of light to a single focus, thus overcoming chromatic aberration. It was first successfully made by Joseph von Fraunhofer.
	is a kind of lens
achromatic objective	has definition A lens of two or more components with different refraction indices (e.g., crown glass and flint glass), used to correct for chromatic aberration.
	is a kind of achromatic lens
actinide	has atomic number 89 to 103
	has definition Element with atomic number between 89 (Actinium) and 103
	has filling orbital 5f
	is a kind of inner transition metal
	is a kind of inner transition metal
	is a kind of metal
actinium	has abundance minute traces in Earth's crust
	has abundance n.a. in Sun relative to H = 1 × 1012
	has abundance nil in seawater
	has atomic emission line 383.312 nm for Ac II
	has atomic emission line 408.844 nm for Ac II
	has atomic emission line 450.720 nm for Ac II
	has atomic emission line 591.085 nm for Ac II
	has atomic emission line 416.840 nm for Ac II (strong)
	has atomic emission line 438.641 nm for Ac II (strong)
	has atomic number 89
	has atomic radii 188 pm
	has biological role none
	has boiling point 3470 ± 300 K
	has chief source uranium ore contain 0.2 p.p.m.
	has crystal cell dimension a = 531.1 pm
	has crystal type f.c.c.
	has daily dietary intake nil
	has definition soft, silvery-white, radioactive metal which glows in the dark
	has density 10060 kg m-3 for solid at 293 K
	has discoverer Andre Debierne
	has discovery date 1899
	has discovery location Paris, France
	has electron configuration [Rn]6d17s2 in ground state
	has electronegativity 1.1 Pauling
	has hazard never encountered normally, dangerous because it is a powerful source of α-radiation, element found only inside nuclear facilities or research laboratories
	has heat capacity 20.84 J K-1 mol-1 for gas at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 27.2 J K-1 mol-1 for solid at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 14.2 kJ mol-1
	has heat of sublimation 51.9 ± 0.5 kJ mol-1
	has heat of vaporization 418 kJ mol-1
	has image
	has ionic radii 118 pm for Ac3+
	has isotope mass range 209 to 232
	has level in humans nil
	has linear expansion coefficient 14.9 K-1
	has longest lived isotope actinium 227
	has mass absorption coefficient cm2 g-1 for CuKα X-ray diffraction
	has mass absorption coefficient cm2 g-1 for MoKα X-ray diffraction
	has mass of element in person nil for a 70 kg average person
	has melting point 1320 ± 50 K
	has molar volume 22.6 cm3
	has name origin aktinos from Greek word for 'ray'
	has number of isotopes 26
	has number of protons 89
	has pronunciation ak-tin-iuhm
	has registry number 7440-34-8 for Chemical Abstracts System database
	has relative atomic mass 227.0728 for 227Ac in units of 12C = 12.000
	has space group Fm3m
	has specimen not commerecially available
	has symbol Ac
	has symbol Ac
	has synthesis mechanism bombardment of radium 236 with neutrons
	has synthesis mechanism decay of uranium 235
	has term symbol 2D3/2 in ground state
	has thermal conductivity 12 W m-1 K-1 at 300 K
	has world production probably less than a gram
	is a kind of actinide
	is a kind of radioactive element
	reacts with water to release hydrogen gas
actinium 224	has atomic mass 224.021685
	has decay mode α (6.323 MeV) 9.1%
	has decay mode γ
	has decay mode EC (1.397 MeV) 90.9%
	has half life 2.9 hours
	has nuclear spin I =
	has number of neutrons 135
	has number of nucleons 224
	has symbol 224Ac
	is an instance of actinium
actinium 225	has atomic mass 225.023205
	has decay mode α (5.935 MeV)
	has decay mode γ
	has half life 10.0 days
	has nuclear spin I = 3/2+
	has number of neutrons 136
	has number of nucleons 225
	has symbol 225Ac
	has uses tracer
	is an instance of actinium
actinium 226	has atomic mass 226.026084
	has decay mode α 6 × 10-3%
	has decay mode β- (1.117) 83 %
	has decay mode γ
	has decay mode EC (0.635 MeV) 17%
	has half life 29 hours
	has nuclear spin I = 1-
	has number of neutrons 137
	has number of nucleons 226
	has symbol 226Ac
	is an instance of actinium
actinium 227	has atomic mass 227.027750
	has decay mode α (5.043 Mev) 1.380%
	has decay mode β- (0.0410 Mev) 98.620%
	has decay mode γ
	has decay products radium 223
	has decay products thorium 227
	has half life 21.773 years
	has magnetogyric ratio 3.5 × 107 rad T-1 s-1
	has NMR frequency 13.1 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity where 13C = 1.00
	has nuclear magnetic moment μ = +1.1
	has nuclear quadrupole moment 1.7 × 10-28 m2
	has nuclear spin I = 3/2-
	has number of neutrons 138
	has number of nucleons 227
	has relative NMR sensitivity where 1H = 1.00
	has symbol 227Ac
	has thermal neutron capture cross section 515 barns
	has uses Nuclear Magnetic Resonance
	is an instance of actinium
actinium 228	has atomic mass 228.031015
	has decay mode β- (2.142 MeV)
	has decay mode γ
	has half life 6.15 hours
	has nuclear spin I = 3+
	has number of neutrons 139
	has number of nucleons 228
	has symbol 228Ac
	is an instance of actinium
actinium 229	has atomic mass 229.032980
	has decay mode β- (0.0410 MeV) 99%
	has decay mode γ
	has half life 62.7 minutes
	has nuclear spin I = 3/2+
	has number of neutrons 140
	has number of nucleons 229
	has symbol 229Ac
	is an instance of actinium
active galaxy	has definition Active galactic nuclei are very luminous. Their energy output is in two forms: nonthermal continuum and thermal emission line.
	has definition Any galaxy which is emitting large quantities of non-thermal radiation.
	has luminosity 1043 to 1046 ergs s-1
	is a kind of galaxy
active optics	has definition Controlling the shape of a telescope mirror at a relatively slow rate.
	is a kind of mirror
active satellite	is a kind of artificial satellite
active Sun	has definition The Sun during its 11-year cycle of activity when spots, flares, prominences, and variations in radiofrequency radiation are at a maximum.
	has period 11 years
	is an instance of periodic celestial event
	is an instance of solar event
adaptive optics	has definition Compensating for atmospheric distortions in a wavefront by high-speed changes in the shape of a small, thin mirror.
	is a kind of mirror
advance of the perihelion	has definition The slow rotation of the major axis of a planet's orbit in the same direction as the revolution of the planet itself, due to gravitational interactions with other planets and/or other effects (such as those due to general relativity).
	is a kind of motion
AE Aurigae	has definition Runaway star which diverges from a comparatively small area in Orion.
	has spectral type O9.5 V
	is a part of Auriga
	is an instance of dwarf
	is an instance of O star
	is an instance of runaway star
Ae star	has definition A-type star with emission in one or several Balmer lines.
	has emission line one or several Balmer lines
	is a kind of A star
	is a kind of emission line star
aeon	has definition In astronomical terms, 1000 million years.
	has synonym eon
	is an instance of time unit
aether	has definition In Aristotelian physics, the fifth element, of which the stars and planets are made.
	has definition In Classical physics, an invisible medium that was thought to suffuse all space.
	is a kind of outdated belief
AI Velorum star	has definition A class of dwarf Cepheids. They are all RR Lyrae stars with periods shorter than 0.25 days.
	is a kind of dwarf Cepheid
airborne telescope	is a kind of telescope
airglow	has definition Light in the nighttime sky caused by the collision of atoms and molecules (primarily oxygen, OH, and Ne) in Earth's geocorona with charged particles and X-rays from the Sun or outer space. The airglow varies with time of night, latitude, and season. It is a minimum at zenith and maximum about 10° above the horizon.
	has synonym nightglow
	is a part of geocorona
alchemy	has definition Art of bringing parts of the universe to the perfect state toward which they were thought to aspire - e.g., gold for metals, immortality for human beings.
	is a kind of outdated belief
Aldebaran	has B-V magnitude 1.54
	has declination +16 30 33
	has definition A K5 III subgiant (a foreground star in the Hyades). It has a faint M2 V companion. It is now known to be slowly and irregularly variable.
	has distance 21 parsecs
	has right ascension 4 35 55.2
	has spectral type K5III
	has synonym alpha Tau
	has synonym HR 1457
	has V magnitude 0.85
	is a part of Taurus
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Algol	has definition An eclipsing system of at least three components (B8 V, K0, Am). Period of components A and B is about 68.8 hours; period of components A, B, and C is about 1.9 years. Long term observations also indicate a massive, unseen fourth component with a period of about 190 years. Algol is also an erratic radio source of about 0.5 AU diameter.
	has definition The most famous eclipsing binary, Algol was probably the first variable star discovered. It lies in the constellation Perseus and consists of two stars that orbit each other every 2.87 days. When one star passes in front of the other, the light of the system dims.
	has distance 25 pc
	has synonym beta Per
	has synonym Demon star
	is a part of Perseus
	is an instance of beta Persei star
alkali earth metal	has definition Element in the second column of the periodic table (from the left)
alkali Earth metal	has group 2
alkali earth metal	has hardness malleable, extrudable and machinable
alkali Earth metal	has synonym group II element
	is a kind of column grouped element
alkali earth metal	is a kind of metallic element
alkali metal	has appearancee silvery except for francium
	has definition Metal in the first column of the periodic table
	has group 1
	has hardness soft
	has synonym group I element
	is a kind of column grouped element
	is a kind of metallic element
	reacts with water vigorously
Alpha Andromedae	has B-V magnitude -0.11
	has declination +29 05 26
	has right ascension 00 08 23.2
	has spectral type B8IVpMnHg
	has synonym HR 15
	has V magnitude 2.06
	is a part of Andromeda
	is an instance of B star
	is an instance of naked eye star
	is an instance of subgiant
Alpha Antliae	has B-V magnitude 1.45
	has declination -31 04 04
	has right ascension 10 27 09.1
	has spectral type K4III
	has synonym HR 4104
	has V magnitude 4.25
	is a part of Antlia
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Alpha Apodis	has B-V magnitude 1.43
	has declination -79 02 41
	has right ascension 14 47 51.6
	has spectral type K2.5III
	has synonym HR 5470
	has V magnitude 3.83
	is a part of Apus
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Alpha Arietis	has B-V magnitude 1.15
	has declination +23 27 45
	has right ascension 02 07 10.3
	has spectral type K2IIIabCa-I
	has synonym HR 617
	has V magnitude 2.00
	is a part of Aries
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Alpha Caeli	has B-V magnitude 0.34
	has declination -41 51 50
	has right ascension 4 40 33.6
	has spectral type F2V
	has synonym HR 1502
	has V magnitude 4.45
	is a part of Caelum
	is an instance of dwarf
	is an instance of F star
	is an instance of naked eye star
Alpha Cassiopeiae	has B-V magnitude 1.17
	has declination +56 32 15
	has right ascension 0 40 30.4
	has spectral type K0III
	has synonym HR 168
	has V magnitude 2.23
	is a part of Cassiopeia
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
alpha Centauri	has B-V magnitude 0.71
	has declination -60 50 07
	has definition A binary star whose components have G2 V and K5 V spectral types. The nearest star system to the Sun and the third brightest star in the night sky.
	has distance 4.35 light-years
	has period 80 years
	has proper motion 3'.68 per year
	has right ascension 14 39 36.2
	has spectral type G2V
	has synonym HR 5459
	has synonym Rigil Kent
	has V magnitude -0.01
	is a part of Centaurus
	is an instance of binary star
	is an instance of dwarf
	is an instance of G star
	is an instance of naked eye star
Alpha Cephei	has B-V magnitude 0.22
	has declination +62 35 08
	has right ascension 21 18 34.7
	has spectral type A7V
	has synonym HR 8162
	has V magnitude 2.44
	is a part of Cepheus
	is an instance of A star
	is an instance of dwarf
	is an instance of naked eye star
Alpha Chamaeleontis	has B-V magnitude 0.39
	has declination -76 55 11
	has right ascension 08 18 31.7
	has spectral type F5III
	has synonym HR 3318
	has V magnitude 4.07
	is a part of Chamaeleon
	is an instance of F star
	is an instance of giant
	is an instance of naked eye star
Alpha Circini	has B-V magnitude 0.24
	has declination -64 58 31
	has right ascension 14 42 30.3
	has spectral type ApSrEuCr:
	has synonym HR 5463
	has V magnitude 3.19
	is a part of Circinus
	is an instance of A star
	is an instance of naked eye star
Alpha Columbae	has B-V magnitude -0.12
	has declination -34 04 27
	has right ascension 05 39 38.9
	has spectral type B7IVe
	has synonym HR 1956
	has V magnitude 2.64
	is a part of Columba
	is an instance of B star
	is an instance of naked eye star
	is an instance of subgiant
Alpha Comae Berenices	has B-V magnitude 0.00
	has declination +17 31 46
	has right ascension 13 09 59.2
	has spectral type F5V
	has synonym HR 4969
	has V magnitude 5.22
	is a part of Coma Berenices
	is an instance of dwarf
	is an instance of F star
Alpha Coronae Autralis	has B-V magnitude 0.04
	has declination -37 54 16
	has right ascension 19 09 28.2
	has spectral type A2V
	has synonym HR 7254
	has V magnitude 4.11
	is a part of Corona Australis
	is an instance of A star
	is an instance of dwarf
	is an instance of naked eye star
Alpha Coronae Borealis	has B-V magnitude -0.02
	has declination +26 42 53
	has right ascension 15 34 41.2
	has spectral type A0V
	has synonym HR 5793
	has V magnitude 2.23
	is a part of Corona Borealis
	is an instance of A star
	is an instance of dwarf
	is an instance of naked eye star
alpha decay	has definition Spontaneous emission by a heavier element (such as uranium) of positively charged helium nuclei - alpha particles - comprising 2 protons and 2 neutrons. The result of this radioactive decay is that the original element is very gradually converted into another element, with a decreased atomic number and mass. Alpha particle emission may be simultaneous with beta particle decay.
	has definition The disintegration of an atomic nucleus, in which the final products are an alpha particle and a nucleus with two fewer protons and two fewer neutrons than the original.
	is a kind of nuclear decay
Alpha Doradus	has B-V magnitude -0.10
	has declination -55 2 42
	has right ascension 4 33 59.8
	has spectral type A0IIISi
	has synonym HR 1465
	has V magnitude 3.27
	is a part of Dorado
	is an instance of A star
	is an instance of giant
	is an instance of naked eye star
Alpha Equulei	has B-V magnitude 0.53
	has declination + 5 14 52
	has right ascension 21 15 49.3
	has spectral type G0III+A5V
	has synonym HR 8131
	has V magnitude 3.92
	is a part of Equuleus
	is an instance of G star
	is an instance of giant
	is an instance of naked eye star
Alpha Fornacis	has B-V magnitude 0.52
	has declination -28 59 14
	has right ascension 03 12 04.2
	has spectral type F8V
	has synonym HR 963
	has V magnitude 3.87
	is a part of Fornax
	is an instance of dwarf
	is an instance of F star
	is an instance of naked eye star
Alpha Gruis	has B-V magnitude -0.13
	has declination -46 57 40
	has right ascension 22 8 13.9
	has spectral type B7IV
	has synonym HR 8425
	has V magnitude 1.74
	is a part of Grus
	is an instance of B star
	is an instance of naked eye star
	is an instance of subgiant
Alpha Horologii	has B-V magnitude 1.10
	has declination -42 17 40
	has right ascension 04 14 00.1
	has spectral type K1III
	has synonym HR 1326
	has V magnitude 3.86
	is a part of Horologium
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Alpha Hydrae	has B-V magnitude 1.44
	has declination -8 39 31
	has right ascension 9 27 35.2
	has spectral type K3II-III
	has synonym Alphard
	has synonym HR 3748
	has V magnitude 1.98
	is a part of Hydra
	is an instance of bright giant
	is an instance of K star
	is an instance of naked eye star
Alpha Indi	has B-V magnitude 1.00
	has declination -47 17 29
	has right ascension 20 37 34.0
	has spectral type K0IIICNIII-IV
	has synonym HR 7869
	has V magnitude 3.11
	is a part of Indus
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Alpha Lacertae	has B-V magnitude 0.01
	has declination +50 16 57
	has right ascension 22 31 17.4
	has spectral type A1V
	has synonym HR 8585
	has V magnitude 3.77
	is a part of Lacerta
	is an instance of A star
	is an instance of dwarf
	is an instance of naked eye star
Alpha Leonis	has B-V magnitude -0.11
	has declination +11 58 2
	has right ascension 10 8 22.3
	has spectral type B7V
	has synonym HR 3982
	has V magnitude 1.35
	is a part of Leo
	is an instance of B star
	is an instance of dwarf
	is an instance of naked eye star
Alpha Leporis	has B-V magnitude 0.21
	has declination -17 49 20
	has right ascension 05 32 43.7
	has spectral type F0Ib
	has synonym HR 1865
	has V magnitude 2.58
	is a part of Lepus
	is an instance of F star
	is an instance of naked eye star
Alpha Lupi	has B-V magnitude -0.20
	has declination -47 23 17
	has right ascension 14 41 55.7
	has spectral type B1.5III
	has synonym HR 5469
	has V magnitude 2.30
	is a part of Lupus
	is an instance of B star
	is an instance of giant
	is an instance of naked eye star
Alpha Lyncis	has B-V magnitude 1.55
	has declination +34 23 33
	has right ascension 9 21 3.2
	has spectral type K7IIIab
	has synonym HR 3705
	has V magnitude 3.13
	is a part of Lynx
	is an instance of bright giant
	is an instance of K star
	is an instance of naked eye star
Alpha Mensae	has B-V magnitude 0.72
	has declination -74 45 11
	has right ascension 06 10 14.6
	has spectral type G6V
	has synonym HR 2261
	has V magnitude 5.09
	is a part of Mensa
	is an instance of dwarf
	is an instance of G star
Alpha Monocerotis	has B-V magnitude 1.02
	has declination -09 33 04
	has right ascension 07 41 14.8
	has spectral type K0III
	has synonym HR 2970
	has V magnitude 3.93
	is a part of Monoceros
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Alpha Muscae	has B-V magnitude -0.20
	has declination -69 08 08
	has right ascension 12 37 11.0
	has spectral type B2IV-V
	has synonym HR 4798
	has V magnitude 2.69
	is a part of Musca
	is an instance of B star
	is an instance of naked eye star
	is an instance of subgiant
Alpha Ophiuchi	has B-V magnitude 0.15
	has declination +12 33 36
	has right ascension 17 34 56.0
	has spectral type A5III
	has synonym HR 6556
	has V magnitude 2.08
	is a part of Ophiuchus
	is an instance of A star
	is an instance of giant
	is an instance of naked eye star
alpha particle mass	applies to particle alpha particle
	has symbol mα
	has uncertainty 0.00000052 × 10-27 kg
	has value 6.64465598 × 10-27 kg
	is an instance of particle mass
Alpha Pavonis	has B-V magnitude -0.20
	has declination -56 44 07
	has right ascension 20 25 38.8
	has spectral type B2IV
	has synonym HR 7790
	has V magnitude 1.94
	is a part of Pavo
	is an instance of B star
	is an instance of naked eye star
	is an instance of subgiant
Alpha Persei	has B-V magnitude 0.48
	has declination +49 51 41
	has right ascension 3 24 19.3
	has spectral type F5Ib
	has synonym HR 1017
	has V magnitude 1.79
	is a part of Perseus
	is an instance of F star
	is an instance of naked eye star
	is an instance of supergiant
alpha Persei cluster	has definition A young open cluster with a high mean rotational velocity.
	is a part of Perseus
	is an instance of open cluster
Alpha Phoenicis	has B-V magnitude 1.09
	has declination -42 18 22
	has right ascension 0 26 17.0
	has spectral type K0III
	has synonym HR 99
	has V magnitude 2.39
	is a part of Phoenix
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Alpha Pictoris	has B-V magnitude 0.21
	has declination -61 56 29
	has right ascension 06 48 11.4
	has spectral type A7IV
	has synonym HR 2550
	has V magnitude 3.27
	is a part of Pictor
	is an instance of A star
	is an instance of naked eye star
	is an instance of subgiant
Alpha Pyxidis	has B-V magnitude -0.18
	has declination -33 11 11
	has right ascension 08 43 35.5
	has spectral type B1.5III
	has synonym HR 3468
	has V magnitude 3.68
	is a part of Pyxis
	is an instance of B star
	is an instance of giant
	is an instance of naked eye star
Alpha Reticuli	has B-V magnitude 0.91
	has declination -62 28 26
	has right ascension 04 14 25.5
	has spectral type G8II-III
	has synonym HR 1336
	has V magnitude 3.35
	is a part of Reticulum
	is an instance of bright giant
	is an instance of G star
	is an instance of naked eye star
Alpha Sculptoris	has B-V magnitude -0.16
	has declination -29 21 28
	has right ascension 0 58 36.3
	has spectral type B7IIIp
	has synonym HR 280
	has V magnitude 4.31
	is a part of Sculptor
	is an instance of B star
	is an instance of bright giant
	is an instance of naked eye star
Alpha Scuti	has B-V magnitude 1.33
	has declination -08 14 39
	has right ascension 18 35 12.3
	has spectral type K3III-IIIb
	has synonym HR 6973
	has V magnitude 3.85
	is a part of Scutum
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Alpha Serpentis	has B-V magnitude 1.17
	has declination +6 25 32
	has right ascension 15 44 16.0
	has spectral type K2IIIbCN1Fe414
	has synonym HR 5854
	has V magnitude 2.65
	is a part of Serpens
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Alpha Sextantis	has B-V magnitude -0.04
	has declination -0 22 18
	has right ascension 10 7 56.2
	has spectral type A0III
	has synonym HR 3981
	has V magnitude 4.49
	is a part of Sextans
	is an instance of A star
	is an instance of giant
	is an instance of naked eye star
Alpha Telescopii	has B-V magnitude -0.17
	has declination -45 58 06
	has right ascension 18 26 58.3
	has spectral type B3IV
	has synonym HR 6897
	has V magnitude 3.51
	is a part of Telescopium
	is an instance of B star
	is an instance of naked eye star
	is an instance of subgiant
Alpha Trianguli Australis	has B-V magnitude 1.44
	has declination -69 01 40
	has right ascension 16 48 39.9
	has spectral type K2IIb-IIIa
	has synonym HR 6217
	has V magnitude 1.92
	is a part of Triangulum Australe
	is an instance of bright giant
	is an instance of K star
	is an instance of naked eye star
Alpha Tucanae	has B-V magnitude 1.39
	has declination -60 15 35
	has right ascension 22 18 30.1
	has spectral type K3III
	has synonym HR 8502
	has V magnitude 2.86
	is a part of Tucana
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Alpha Vulpeculae	has B-V magnitude 1.50
	has declination +24 39 54
	has right ascension 19 28 42.2
	has spectral type M0III
	has synonym HR 7405
	has V magnitude 4.44
	is a part of Vulpecula
	is an instance of giant
	is an instance of M star
	is an instance of naked eye star
alpha-particle	has definition Nucleus formed by the α-process (q.v.) (see even-even nuclei).
	has definition Particle first discovered in radioactive α decay, and later identified as helium nuclei (two protons and two neutrons bound together).
	has definition The nucleus of a 4He atom, consisting of two protons and two neutrons. Mass of α-particle 4.00260 amu.
	is an instance of 4N nucleus
alpha-process	has definition A hypothetical process of nucleosynthesis, which consisted of redistributing α-particles in the region from neon 20 to iron 56 (and perhaps slightly higher). The α-process has been replaced by explosive and nonexplosive C, O, and Si burning occurring in rapidly evolving or even explosive stages of stellar evolution which at higher temperatures and densities becomes the e-process.
	is a kind of nucleosynthetic reaction
alpha2 CVn	has definition A spectrum variable with spectrum showing strong, profuse lines of rare earths, iron-peak elements, and Si.
	has period 5.469 days
	is a part of Canes Venatici
	is an instance of spectrum variable
Altair	has apparent magnitude mv = 0.78
	has B-V magnitude 0.22
	has declination +08 52 06
	has definition A bright A7 V star.
	has distance 4.8 pc
	has right ascension 19 50 46.9
	has spectral type A7 V
	has synonym alpha Aql
	has synonym HR 7557
	has V magnitude 0.77
	is a part of Aquila
	is an instance of A star
	is an instance of dwarf
	is an instance of naked eye star
altazimuth telescope	has definition A form of mounting similar to that of a radar which allows the telescope tube to be moved horizontally (by rotation in azimuth or compass direction) and vertically (by rotation in altitude or elevation). To follow a star the telescope must be adjusted simultaneously in both axes. (also called alt-az)
	has mounting altazimuth
	is a kind of Earth based telescope
aluminium	has abundance 0.13 × 10-4 p.p.m. in deep Pacific seawater
	has abundance 1.3 × 10-4 p.p.m. in Pacific surface seawater
	has abundance 3.3 × 106 in Sun relative to H = 1 × 1012
	has abundance 5.2 × 10-4 p.p.m. in deep Atlantic seawater
	has abundance 82000 p.p.m. in Earth's crust
	has abundance 9.7 × 10-4 p.p.m. in Atlantic surface seawater
	has atomic emission line 308.215 nm for Al I
	has atomic emission line 309.271 nm for Al I (used in atom absorption spectrometry)
	has atomic emission line 309.281 nm for Al I (used in atom absorption spectrometry)
	has atomic emission line 394.401 nm for Al I
	has atomic emission line 396.152 nm for Al I (strong)
	has atomic number 13
	has atomic radii 143 pm
	has biological role none
	has boiling point 2740 K
	has bulk modulus 75.2 GPa
	has chief source bauxite
	has covalent radii 125 pm
	has crystal cell dimension a = 404.959 pm
	has crystal type f.c.c.
	has daily dietary intake 2.45 mg
	has definition soft and malleable metal
	has density 2390 kg m-3 for liquid at 933.52 K melting point
	has density 2698 kg m-3 for solid at 293 K
	has discoverer Oersted
	has discovery date 1825
	has discovery location Copenhagen, Denmark
	has electrical resistivity 2.6548 × 108 Ω m at 293 K
	has electron affinity 44 kJ mol-1 from Al to Al-
	has electron configuration [Ne]3s23p1 in ground state
	has electronegativity 1.61 Pauling
	has hazard accumulates in the body from daily intake, compounds are used as food additives and in indigestion tablets
	has heat capacity 21.38 J K-1 mol-1 for gas at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 24.35 J K-1 mol-1 for solid at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 10.67 kJ mol-1
	has heat of vaporization 293.72 kJ mol-1
	has image
	has ionic radii 57 pm for Al3+
	has isotope mass range 22 to 31
	has level in human blood 0.39 mg dm-3
	has level in human bone 4 - 27 p.p.m.
	has level in human liver 3 - 23 p.p.m.
	has level in human muscle 0.7 - 28 p.p.m.
	has linear expansion coefficient 23.03 K-1
	has longest lived isotope aluminium 27 which is stable
	has main mining area Surinam, Jamaica, Ghana, Indonesia, Russia
	has mass absorption coefficient 48.6 cm2 g-1 for CuKα X-ray diffraction
	has mass absorption coefficient 5.16 cm2 g-1 for MoKα X-ray diffraction
	has mass magnetic susceptibility 7.7 × 109 kg-1 m3 for solid
	has mass of element in person 60 mg for a 70 kg average person
	has melting point 933.52 K
	has mineral bauxite, boehmite, diaspore, gibbsite, andalusite, corundum, sillimanite, topaz
	has molar volume 10.00 cm3
	has name origin alumen = alum from latin
	has neutron scattering length 0.3449 × 10-12 cm
	has number of isotopes 11
	has number of protons 13
	has ocean oxidation state III
	has ocean residence time 150 years
	has poisson's ratio 0.345 GPa
	has pronunciation al-oo-min-iuhm
	has registry number 7429-90-5 for Chemical Abstracts System database
	has relative atomic mass 26.981539 in units of 12C = 12.000
	has reserves 6 × 106 tonnes
has rigidity modulus 26.2 GPa
has space group Fm3m
has specimen foil, granules, ingots, pellets, powder, rod, shot or wire. Safe. Aluminum powder can react dangerously with other materials.
has symbol Al
has term symbol 2P1/2 in ground state
has thermal conductivity 237 W m-1 K-1 at 300 K
has toxic intake 5 g
has uses vehicle, aircraft and construction industries
has van der Waals radii 205 pm
has world production 15 × 106 tonnes per year
has young's modulus 70.6 GPa
is a kind of accumulating oceanic element
is a kind of group III element
is a kind of metallic element
reacts with air to produce a thin protective oxide layer
stable isotope aluminium 27
aluminium 26	has atomic mass 25.986892
	has decay mode β+ (4.005 Mev) 82%
	has decay mode γ
	has decay mode EC 18%
	has decay product magnesium 26
	has diagnostic role if decay products found in a solid then solid must have condensed within the first million years after the creation of Al 26
	has half life 7.2 × 105 years
	has nuclear spin I = 5+
	has number of neutrons 13
	has number of nucleons 26
	has symbol 26Al
	has uses research
	is an instance of aluminium
	is an instance of supernova produced radioactive element
aluminium 27	has atomic mass 26.9885386
	has magnetogyric ratio 6.9704 × 107 rad T-1 s-1
	has NMR frequency 26.057 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 1.17 × 103 where 13C = 1.00
	has nuclear magnetic moment μ = 3.641504
	has nuclear quadrupole moment 0.1403 × 10-28 m2
	has nuclear spin I = 5/2+
	has number of neutrons 14
	has number of nucleons 27
	has relative NMR sensitivity 0.21 where 1H = 1.00
	has symbol 27Al
	has thermal neutron capture cross section 0.231 barns
	has uses Nuclear Magnetic Resonance
	is an instance of aluminium
aluminium 28	has atomic mass 27.981910
	has decay mode β- (4.642 Mev)
	has decay mode γ
	has half life 2.25 minutes
	has nuclear magnetic moment μ = 3.24
	has nuclear spin I = 3+
	has number of neutrons 15
	has number of nucleons 28
	has symbol 28Al
	is an instance of aluminium
aluminium 29	has atomic mass 28.980446
	has decay mode β- (3.68 Mev) %
	has decay mode γ
	has half life 6.5 minutes
	has nuclear spin I = 5/2+
	has number of neutrons 16
	has number of nucleons 29
	has symbol 29Al
	is an instance of aluminium
Am star	has definition A-type or F-type object to which no unique spectral type can be assigned. Usually the classifier provides a classification according to the hydrogen, metallic and calcium lines. Also call metallic-line stars.
	has definition Peculiar star whose metallic lines are as strong as those of the F stars but whose hydrogen lines are so strong as to require that they be classed with the A stars. They are generally short-period (<300d) spectroscopic binaries with high atmospheric turbulence and variable spectra, and are slower rotators than normal A stars.
	is a kind of A star
	is a kind of peculiar star
Amalthea	has definition The innermost satellite of Jupiter.
	has diameter 140 km
	has discoverer Barnard
	has discovery date 1892
	has eccentricity e = 0.0028
	has inclination i = 0°.4
	has orbital period 0.498 days
	has synonym Barnard's satellite
	has synonym Jupiter V
	is a part of Jupiter
	is an instance of natural satellite
americium	has abundance nil in Earth's crust
	has abundance nil in seawater
	has atomic emission line 367.312 nm for Am I
	has atomic emission line 377.750 nm for Am II
	has atomic emission line 392.625 nm for Am II
	has atomic emission line 408.929 nm for Am II
	has atomic emission line 428.926 nm for Am I
	has atomic emission line 450.945 nm for Am II
	has atomic emission line 457.559 nm for Am II
	has atomic emission line 466.279 nm for Am II
	has atomic emission line 605.464 nm for Am I (strong)
	has atomic number 95
	has atomic radii 173 pm
	has biological role none
	has boiling point 2880 K
	has crystal cell dimension a = 346.80 pm for α phase
	has crystal cell dimension a = 489.4 pm for β phase
	has crystal type f.c.c. for β phase
	has crystal type h.c.p. for α phase
	has daily dietary intake nil
	has definition radioactive silvery metal which does not occur naturally
	has density 13670 kg m-3 for solid at 293 K
	has discoverer Glen T. Seaborg, R.A. James, L.O. Morgan, and A. Ghiorso
	has discovery date 1944
	has discovery location Chicago, Illinois, US
	has electrical resistivity 68 × 10-8 Ω m
	has electron configuration [Rn]5f77s2 in ground state
	has electronegativity 1.3 Pauling
	has hazard intense α-radiation, maximum permissible body burden of 241Am is 0.03 μCi - it targets bone. γ radiation is a problem in gram amounts.
	has heat of fusion 14.4 kJ mol-1
	has heat of sublimation 34.2 kJ mol-1
	has heat of vaporization 284 kJ mol-1
	has image
	has ionic radii 107 pm for Am3+
	has ionic radii 80 pm for Am6+
	has ionic radii 86 pm for Am5+
	has ionic radii 92 pm for Am4+
	has isotope mass range 227 to 247
	has level in humans nil
	has longest lived isotope americium 243
	has mass magnetic susceptibility +5 × 10-8 kg-1 m3
	has mass of element in person nil for a 70 kg average person
	has melting point 1445 K
	has mineral none
	has molar volume 17.78 cm3
	has name origin america from English
	has neutron scattering length 0.83 in 10-12 cm units
	has number of isotopes 23 including nuclear isomers
	has number of protons 95
	has phase changed temperature 1347 K at α to β phase crystal transition
	has pronunciation amer-is-iuhm
	has registry number 7440-35-9 for Chemical Abstracts System database
	has relative atomic mass 243.0614 for americium 243 in units of 12C = 12.000
	has space group Fm3m for β phase
	has space group P63/mmc for α phase
	has symbol Am
	has term symbol 8S7/2 in ground state
	has thermal conductivity 10 W m-1 K-1 at 300 K
	has thermal neutron capture cross section 75.3 barns
	has uses source of radiation for γ-radiotherapy
	has world production probably a few kilograms per year
	is a kind of radioactive element
	is a kind of transuranium element
	reacts with air, steam and acids, but not alkalis
americium 237	has atomic mass 237.050050
	has decay mode α (6.20 Mev) 0.02%
	has decay mode γ
	has decay mode EC (1.6 Mev) 99.98%
	has half life 1.22 hours
	has nuclear spin I = 5/2-
	has number of neutrons 142
	has number of nucleons 237
	has symbol 237Am
	is an instance of americium
americium 238	has atomic mass 238.051980
	has decay mode α (6.04 Mev) < 0.1%
	has decay mode γ
	has decay mode EC (2.26 MeV)
	has half life 1.63 hours
	has nuclear spin I = 1+
	has number of neutrons 143
	has number of nucleons 238
	has symbol 238Am
	is an instance of americium
americium 239	has atomic mass 239.053016
	has decay mode α (5.924 Mev) 0.01%
	has decay mode γ
	has decay mode EC (0.800 MeV) 99.99%
	has half life 11.9 hours
	has nuclear spin I = 5/2-
	has number of neutrons 144
	has number of nucleons 239
	has symbol 239Am
	is an instance of americium
americium 240	has atomic mass 240.055278
	has decay mode α (5.592 Mev)
	has decay mode γ
	has decay mode EC (1.38 MeV)
	has half life 2.12 days
	has nuclear spin I = 3-
	has number of neutrons 145
	has number of nucleons 240
	has symbol 240Am
	is an instance of americium
americium 241	has atomic mass 241.056823
	has decay mode α (5.637 Mev) %
	has decay mode γ
	has half life 432.2 years
	has nuclear magnetic moment μ = 1.61
	has nuclear spin I = 5/2-
	has number of neutrons 146
	has number of nucleons 241
	has specimen commercially available, under licence
	has symbol 241Am
	has synthesis mechanism 241Pu subjected to neutron bombardment over a period of years
	has uses research, medical therapy, medical diagnosis
	is an instance of americium
americium 242	has atomic mass 242.056541
	has decay mode β- (0.663 Mev) 83%
	has decay mode γ
	has decay mode EC (0.750 Mev) 17%
	has half life
	has nuclear magnetic moment μ = +0.388
	has nuclear spin I = 1-
	has number of neutrons 147
	has number of nucleons 242
	has symbol 242Am
	is an instance of americium
americium 242m	has decay mode α (5.62 Mev) 0.5%
	has decay mode γ
	has decay mode IT (0.48 Mev) 99.5%
	has half life 141 years
	has nuclear magnetic moment μ = 1.0
	has nuclear spin I = 5-
	has number of neutrons 147
	has number of nucleons 242
	has symbol 242mAm
	is an instance of americium
americium 243	has atomic mass 243.061375
	has decay mode α (5.438 Mev)
	has decay mode γ
	has half life 7370 years
	has magnetogyric ratio 1.54 × 107 rad T-1 s-1
	has NMR frequency 5.76 MHz where 1H = 100 MHz; 2.3488 T
	has nuclear magnetic moment μ = 1.61
	has nuclear quadrupole moment +4.210 × 10-28 m2
	has nuclear spin I = 5/2-
	has number of neutrons 148
	has number of nucleons 243
	has specimen commercially available, under licence
	has symbol 243Am
	has synthesis mechanism 239Pu subjected to neutron bombardment
	has uses research, Nuclear Magnetic Resonance
	is an instance of americium
americium 244	has atomic mass 244.064279
	has decay mode β- (1.427 Mev)
	has decay mode γ
	has half life 10.0 hours
	has number of neutrons 149
	has number of nucleons 244
	has symbol 244Am
	is an instance of americium
americium 245	has atomic mass 245.066444
	has decay mode β- (0.894 Mev)
	has decay mode γ
	has half life 2.05 hours
	has nuclear spin I = 5/2+
	has number of neutrons 150
	has number of nucleons 245
	has symbol 245Am
	is an instance of americium
ammonia	has symbol NH3
	is an instance of interstellar molecule
	is an instance of neutral particle
amount of substance unit	is a kind of unit
	is a unit of amount of substance
amount-of-substance concentration unit	has definition mole per cubic meter
	has symbol mol·m-3
	is a kind of derived SI unit
ampere	has consequence fixes the magnetic constant (permeability of vacuum) at exactly 4 × 10-7 H · m-1
	has definition constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per meter of length
	has definition Unit of electric current. "The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per meter of length" (CIPM
	has symbol A
	is an instance of base SI unit
	is an instance of current unit
Andromeda	has acronym And
	has boundary
	has genitive Andromedae
	has historical image
	has synonym Chained Lady
	has synonym Princess of Ethiopia
	is a part of celestial sphere
	is an instance of constellation
Andromeda galaxy	has definition A spiral galaxy (kS5 in Morgan's classification) in the Local Group, about 650-700 kpc distant (MV = -21), visible to the naked eye as a fuzzy patch in the constellation of Andromeda. Total mass about 3.1 × 1011 Msun ; i = 77°, heliocentric velocity - 180 km s-1. Its nucleus exhibits noncircular gas motions. It is similar to but slightly larger than our Galaxy.
	has definition Major spiral galaxy, 2.2 million light-years from Earth. Gravitationally bound to the Milky Way with which it shares membership in the Local Group, it is currently approaching us, rather than receding as is the case for most galaxies.
	has definition The largest galaxy in the Local Group. Also known as the Great Spiral and M31. It is about one and a half times the size of our own galaxy, and contains at least 300 globular clusters. Two smaller, elliptical galaxies (M32 and NGC 205) lie close to it.
	has definition The largest member of the local group. It is a giant spiral galaxy that lies 2.4 million light-years away.
	has image
	has NED data
	has synonym M 31
	is a part of Local Group
	is an instance of galaxy containing Cepheids
	is an instance of hypergalaxy
	is an instance of Messier object
	is an instance of naked eye object
	is an instance of Sb spiral
Andromeda I	has definition Dwarf spheroidal galaxy in the Andromeda subgroup of the Local Group. It is among the intrinsically faintest members of the Local Group.
	has discoverer van den Bergh
	has discovery date 1972
	is a part of Local Group
	is an instance of satellite galaxy
	orbits Andromeda galaxy
Andromeda II	has definition Dwarf spheroidal galaxy in the Andromeda subgroup of the Local Group. It is among the intrinsically faintest members of the Local Group.
	has discoverer van den Bergh
	has discovery date 1972
	is a part of Local Group
	is an instance of satellite galaxy
	orbits Andromeda galaxy
Andromeda III	has definition Dwarf spheroidal galaxy in the Andromeda subgroup of the Local Group. It is among the intrinsically faintest members of the Local Group.
	has discoverer van den Bergh
	has discovery date 1972
	is a part of Local Group
	is an instance of satellite galaxy
	orbits Andromeda galaxy
angle	has unit angle unit
	is a kind of quantity
angle unit	is a kind of unit
	is a unit of angle
Anglo-Australian Telescope	has acronym AAT
	has altitude 1149 m
	has aperture 3.893 m
	has creation date 1975
	has focal ratio t/3.3. 8, 15. 36
	has latitude 31° 17' S
	has location Siding Spring Mtn., Australia
	has longitude 149° 04' E
	has mirror maker Grubb-Parsons
	has mirror type Cer-Vit
	has mounting manufacturer Mitsubishi
	has owner Anglo-Australian Observatory
	is an instance of Horseshoe equatorial telescope
	is an instance of optical telescope
	is an instance of reflector
angstrom	has definition A unit of length used when expressing wavelengths.
	has equivalent 10-10 meters
	has symbol Å
	is an instance of length unit
	is an instance of non SI unit
	is named after Anders Jonas Angstrom (1814-1874)
angular momentum	has definition The angular momentum of a system about a specified origin is the sum over all the particles in the system (or an integral over the different elements of the system if it is continuous) of the vector products of the radius vector joining each particle to the origin and the momentum of the particle. For a closed system it is conserved by virtue of the isotropy of space.
	has definition The product of mass and angular velocity for an object in rotation; similar to linear momentum. In quantum mechanics, angular momentum is quantized, i.e., is measured in indivisible units equivalent to Planck's constant divided by 2 pi. This corresponds classically to only certain frequencies of rotation being allowed.
	has symbol L
	is a kind of quantity
angular size	has definition The angle subtended by an object on the sky. For example, the angular size of the moon is 30 arcminutes.
	is a kind of angle
ANIK 1	is an instance of ANIK satellite
ANIK 2	is an instance of ANIK satellite
ANIK 3	is an instance of ANIK satellite
ANIK satellite	is a kind of geosynchronous satellite
anisotropy	breaks isotropy
	has definition The characteristic of being dependent upon direction. (Light coming with equal intensity from all directions is isotropic; a spotlight's beam is anisotropic.) The cosmic background radiation is generally isotropic - i.e., its intensity is the same in all parts of the sky - but small anisotropies have been detected which are thought to reflect the earth's proper motion relative to the framework of the universe as a whole.
	has definition The condition in which the universe appears different in different directions.
	is a kind of symmetry breaking
Annie Jump Cannon	has career Havard College Observatory
	has greatest achievement the Henry Draper Catalog of spectral types
	is an instance of 19th century scientist
	is an instance of astronomer
annular eclipse	has definition A solar eclipse in which the solar disk is never completely covered but is seen as an annulus or ring at maximum eclipse. An annular eclipse occurs when the apparent disk of the Moon is smaller than that of the Sun.
	has definition An eclipse of the Sun in which the Moon is too far from Earth to block out the Sun completely, so that a ring of sunlight appears around the Moon.
	is an instance of solar eclipse
anomalistic month	has definition The interval between two successive perigee passages of the Moon.
	has value 27.555 days
	is an instance of month
anomalistic year	has definition A period of time based on the revolution of the Earth around the Sun, where a year is defined as the mean interval between successive passages of the Earth through perihelion.
	has definition The interval between two successive perihelion passages of Earth.
	has value 365.2596 ephemeris days
	is an instance of year
anomalous Zeeman effect	has cause the influence of magnetic fields on both the orbital angular momentum and the spin angular momentum of electrons in atoms or ions
	has definition Zeeman effet in which spectral lines are split into several components, in contrast to the normal Zeeman effect which results in only two distinct components.
	has effect splitting of spectral lines into more than two components
	is a kind of Zeeman effect
antapex	has definition The direction in the sky away from which the Sun seems to be moving (at a speed of 19.4 km s-1) relative to general field stars in the Galaxy.
	is a part of Columba
	is an instance of equatorial coordinate
	is opposite of solar apex
Antares	has B-V magnitude 1.83
	has declination -26 25 55
	has definition A red M1 Ib supergiant. It has a B3 V companion, which is a radio source.
	has distance 125 parsecs
	has location inner edge of the Orion spiral arm
	has right ascension 16 29 24.4
	has spectral type M1.5Iab-Ib+B4V
	has synonym alpha Sco
	has synonym HR 6134
	has V magnitude 0.96
	is a part of Scorpius
	is an instance of naked eye star
	is an instance of red supergiant
anthropic principle	has definition The doctrine that the value of certain fundamental constants of nature can be explained by demonstrating that, were they otherwise, the universe could not support life and therefore would contain nobody capable of worrying about why they are as they are. Were the strong nuclear force slightly different in strength, for instance, the stars could not shine and life as we know it would be impossible.
	has definition The weak form of the anthropic principle states that life can exist only during a brief period of the history of our universe. The strong form of the principle states that out of all possible values for the fundamental constants of nature and the initial conditions of the universe, only a small fraction could allow life to form at all, at anytime. (See boundary conditions; fundamental constants of nature.)
	is a kind of outdated belief
anthropocentrism	has definition The belief that humans are central to the universe.
	is a kind of outdated belief
anthropomorphism	has definition The projection of human attributes onto nonhuman entities such as animals, the planets, or the universe as a whole.
	is a kind of outdated belief
anti-reflection coating	has definition Also AR coating. A layer of material of lower refractive index of just the right thickness (1/4 wave) is deposited on the optical surface to be coated. More complex coatings are possible which cover a large wavelength range.
	is a kind of coating
anticenter	has definition The direction of the sky opposite to that of the galactic center.
	has definition The point in the galactic plane that lies directly opposite the galactic center. Here we gaze toward the edge of the Galactic disk. The nearest bright star to the anticenter is El Nath, in the constellation Taurus.
	has galactic latitude 0
	has galactic longitude 180 degrees
	is a part of Auriga
	is an instance of galactic coordinate
	is opposite of galactic center
antimony	has abundance 0.2 p.p.m. in Earth's crust
	has abundance 10 in Sun relative to H = 1 × 1012
	has abundance 3 × 10-4 p.p.m. in seawater
	has atomic emission line 206.833 nm for Sb I
	has atomic emission line 217.581 nm for Sb I
	has atomic emission line 252.852 nm for Sb I
	has atomic emission line 259.805 nm for Sb I
	has atomic emission line 231.147 nm for Sb I (strong)
	has atomic number 51
	has atomic radii 182 pm
	has biological role none
	has boiling point 1908 K
	has chief source stibnite, tetrahedrite although mainly a copper ore yields antimony as a by-product
	has covalent radii 141 pm
	has crystal cell dimension a = 298.6 pm for grey cubic form
	has crystal cell dimension a = 336.9 pm for metal form
	has crystal cell dimension a = 430.84 pm for grey rhombohedral form
	has crystal cell dimension c = 1124.7 pm for grey rhombohedral form
	has crystal cell dimension c = 533 pm for metal form
	has crystal type cubic for grey cubic form
	has crystal type h.c.p. for metal form
	has crystal type rhombohedral for grey rhombohedral form
	has daily dietary intake 0.002 to 1.3 mg
	has definition metalloid element with three forms. The metallic form is the more stable and is bright, silvery, hard and brittle
	has density 6483 kg m-3 for liquid at 903.89 K melting point
	has density 6691 kg m-3 for solid at 293 K
	has discovery date 1600 BC probably known to the ancients and certainly to the alchemists
	has electrical resistivity 39.0 × 10-8 Ω m at 273 K
	has electron affinity 101 kJ mol-1 from Sb to Sb-
	has electron configuration [Kr]4d105s25p3 in ground state
	has electronegativity 2.05 Pauling
	has hazard small doses stimulate metabolism, large doses cause liver damage
	has heat capacity 20.79 J K-1 mol-1 for gas at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 25.23 J K-1 mol-1 for solid at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 20.9 kJ mol-1
	has heat of vaporization 67.91 kJ mol-1
	has image
	has ionic radii 245 pm for Sb2-
	has ionic radii 62 pm for Sb5+
	has ionic radii 89 pm for Sb3+
	has isotope mass range 108 to 136
	has lethal intake 140 mg for antimony potassium tartrate (oral) for LD50
	has level in humans 0.0033 mg dm-3 in blood
	has level in humans 0.01 to 0.6 p.p.m. in bone
	has level in humans 0.011 to 0.42 p.p.m. in liver
	has level in humans 0.042 to 0.191 p.p.m. in muscle
	has linear expansion coefficient 8.5 × 10-6 K-1
	has main mining area China, Italy, Peru, Mexico, Bolivia, France
	has mass absorption coefficient 270 cm2 g-1 for CuKα X-ray diffraction
	has mass absorption coefficient 33.1 cm2 g-1 for MoKα X-ray diffraction
	has mass magnetic susceptibility -1.0 × 10-8 kg-1 m3 for solid
	has mass of element in person 2 mg for a 70 kg average person
	has melting point 903.89 K
	has mineral sibiconite, stibnite, tetrahedrite, ullmannite
	has molar volume 18.20 cm3
	has name origin anti + monos = not alone from greek
	has neutron scattering length 0.557 × 10-12 cm
	has number of isotopes 40
	has number of protons 51
	has ocean oxidation state III
	has ocean residence time 3.5 × 105 years
	has poisson's ratio 0.25 to 0.33 GPa
	has pronunciation anti-moni
	has registry number 7440-36-0 for Chemical Abstracts System database
has relative atomic mass 112.760 in units of 12C = 12.000
has reserves 2.5 × 106 tonnes
has rigidity modulus 20.7 GPa
has space group P63/mmc for metal form
has space group Pm3m for grey cubic form
has space group R3m for grey rhombohedral form
has specimen available as pieces, powder or shot. Care !
has stable isotope antimony 121
has stable isotope antimony 123
has symbol Sb
has symbol origin stibium from latin
has term symbol 4S3/2 in ground state
has thermal conductivity 24.3 W m-1 K-1 at 300 K
has thermal neutron capture cross section 4.91 barns
has toxic intake 100 mg
has uses hardenning other metals, stotage batteries, bearings
has van der Waals radii 220 pm
has world production 53000 tonnes per year
has young's modulus 54.7 GPa
is a kind of accumulating oceanic element
is a kind of group V element
is a kind of metallic metalloid
reacts with stable in dry air, not attacked by dilute acids or alkalis
antimony 119	has atomic mass 118.903948
	has decay mode γ
	has decay mode EC (0.59 Mev)
	has half life 38.1 hours
	has nuclear magnetic moment μ = +3.45
	has nuclear spin I = 5/2+
	has number of neutrons 68
	has number of nucleons 119
	has symbol 119Sb
	is an instance of antimony
antimony 120	has atomic mass 119.903821
	has decay mode β+ (2.68 Mev) 41%
	has decay mode γ
	has decay mode EC 59%
	has half life 15.89 minutes
	has nuclear magnetic moment μ = +2.3
	has nuclear spin I = 1+
	has number of neutrons 69
	has number of nucleons 120
	has symbol 120Sb
	is an instance of antimony
antimony 120m	has atomic mass 119.903821
	has decay mode γ
	has decay mode EC
	has half life 5.76 days
	has nuclear magnetic moment μ = 2.34
	has nuclear spin I = 8-
	has number of neutrons 69
	has number of nucleons 120
	has symbol 120mSb
	is an instance of antimony
antimony 121	has atomic mass 120.9038212
	has magnetogyric ratio 6.4016 × 107 rad T-1 s-1
	has natural abundance 57.3 %
	has NMR frequency 23.930 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 520 where 13C = 1.00
	has nuclear magnetic moment μ = +3.3634
	has nuclear quadrupole moment -0.360 × 10-28 m2
	has nuclear spin I = 5/2+
	has number of neutrons 70
	has number of nucleons 121
	has relative NMR sensitivity 0.16 where 1H = 1.00
	has symbol 121Sb
	has uses experimental, Nuclear Magnetic Resonance
	is an instance of antimony
antimony 122	has atomic mass 121.905179
	has decay mode β+ (0.619 Mev) 2%
	has decay mode β- (1.9820 Mev) 98%
	has decay mode γ
	has half life 2.73 days
	has nuclear magnetic moment μ = -1.90
	has nuclear spin I = 2-
	has number of neutrons 71
	has number of nucleons 122
	has symbol 122Sb
	is an instance of antimony
antimony 123	has atomic mass 122.9042160
	has magnetogyric ratio 3.4668 × 107 rad T-1 s-1
	has natural abundance 42.7 %
	has NMR frequency 12.959 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 111 where 13C = 1.00
	has nuclear magnetic moment μ = 2.5498
	has nuclear quadrupole moment -0.490 × 10-28 m2
	has nuclear spin I = 7/2+
	has number of neutrons 72
	has number of nucleons 123
	has relative NMR sensitivity 4.57 × 10-2 where 1H = 1.00
	has symbol 123Sb
	has uses experimental, Nuclear Magnetic Resonance
	is an instance of antimony
antimony 124	has atomic mass 123.905038
	has decay mode β- (2.905 Mev)
	has decay mode γ
	has half life 60.30 days
	has nuclear magnetic moment μ = 1.2
	has nuclear spin I = 3-
	has number of neutrons 73
	has number of nucleons 124
	has symbol 124Sb
	has uses research
	is an instance of antimony
antimony 125	has atomic mass 124.905252
	has decay mode β- (0.767 Mev)
	has decay mode γ
	has half life 2.758 years
	has nuclear magnetic moment μ = +2.63
	has nuclear spin I = 7/2+
	has number of neutrons 74
	has number of nucleons 125
	has symbol 125Sb
	is an instance of antimony
antimony 126	has atomic mass 125.907250
	has decay mode β- (3.67 Mev) %
	has decay mode γ
	has half life 12.4 days
	has nuclear magnetic moment μ = 1.3
	has nuclear spin I = 8-
	has number of neutrons 75
	has number of nucleons 126
	has symbol 126Sb
	is an instance of antimony
antimony 127	has atomic mass 126.906919
	has decay mode β- (1.58 Mev)
	has decay mode γ
	has half life 3.84 days
	has nuclear magnetic moment μ = 2.6
	has nuclear spin I = 7/2+
	has number of neutrons 76
	has number of nucleons 127
	has symbol 127Sb
	is an instance of antimony
antineutrino	has antiparticle neutrino
	has definition The antiparticle of a neutrino.
	is a kind of antiparticle
	is a kind of lepton
	is a kind of neutral particle
antineutron	has antiparticle neutron
	has definition The antiparticle of a neutron. A neutron and antineutron both have the same mass and zero electric charge, but can be differentiated by their interactions: a neutron and an antineutron can annihilate into gamma rays, while two neutrons cannot.
	is an instance of antiparticle
	is an instance of baryon
	is an instance of neutral particle
	is an instance of radioactive particle
antiparticle	has definition An elementary particle of opposite charge but otherwise identical to its partner. Most of the observable universe consists of particles and matter, as opposed to antiparticles and antimatter.
	has definition Atomic particles that have the same mass as, but opposite charge and orbital direction to, an ordinary particle. Thus, instead of negatively charged electrons, atoms of antimatter have positrons. A quantity of antimatter coming into contact with matter would "cancel out" - annihilate, with total conversion of mass to energy - an exact proportion of matter corresponding to the original quantity of antimatter, provided that the elements in the matter also corresponded with the "elements" in the antimatter, i.e., that the atoms were equivalent but opposite.
	has definition For every known type of particle, there exists an antiparticle with exactly the same mass, but with the opposite electric charge. When a particle and its antiparticle come together, they can always annihilate to form gamma rays. The antiparticle of an electrically neutral particle is sometimes the same as the original particle (e.g., photons) and sometimes it is distinct (e.g., neutrons).
	has definition Particles predicted by combining the theories of special relativity and quantum mechanics. For each particle, there must exist an antiparticle with the opposite charge, magnetic moment and other internal quantum numbers (e.g., lepton number, baryon number, strangeness, charm, etc.), but with the same mass, spin and lifetime. Note that certain neutral particles (such as the photon and π0) are their own antiparticles.
	has definition Particles with identical mass and spin as those of ordinary matter, but with opposite charge. Antimatter has been produced experimentally, but little of it is found in nature. Why this should be so is one of the questions that must be answered by any adequate theory of the early universe.
	is a kind of particle
antiproton	has antiparticle proton
	has charge -1
	has definition The antiparticle of a proton, identical in mass and spin but of opposite (negative) charge.
	is an instance of antiparticle
	is an instance of baryon
	is an instance of charged particle
	is an instance of radioactive particle
antiquark	has antiparticle quark
	has definition The antiparticle of the quark.
	is a kind of antiparticle
	is a kind of charged particle
	is a kind of parton
Antlia	has acronym Ant
	has boundary
	has genitive Antliae
	has synonym Air Pump
	is a part of celestial sphere
	is an instance of constellation named by de Lacaille
Antonia Maury	has career Havard College Observatory
	is an instance of 19th century scientist
	is an instance of astronomer
Ap star	has definition Peculiar A-type stars ("magnetic" A stars) that show abnormally strong lines, sometimes of varying intensity, of certain ionized metals. Recent evidence indicates that all Ap stars are slow rotators compared with normal A stars.
	has definition Star with spectral type A in which the lines of one or several elements are abnormally enhanced. Traditionally the most important subgroups are Si λ4200, Hg-Mn and Cr-Eu-Sr stars. The latest objects of the latter group correspond to early F-type.
	has definition Stars can be classified according to their surface temperatures, which determine, in large part, the spectrum of radiation they emit. A stars have surface temperatures between about 7,500 and 11,000 degrees centigrade. Peculiar A stars are A stars whose emitted radiation spectra have many of the characteristics of A stars but are peculiar in certain ways.
	is a kind of A star
	is a kind of peculiar star
apastron	has antonym periastron
	has definition The point in the orbit of one component of a binary system where it is farthest from the other.
	has participants binary star
	is an instance of binary star orbital event
aphelion	has antonym perihelion
	has definition The point in a planetary orbit that is at the greatest distance from the Sun.
	is an instance of Sun orbital event
aplanatic system	has definition A system of three lenses which, taken together, correct for spherical aberration, chromatic aberration, and coma.
	is a kind of lens
apocenter	has antonym pericenter
	has definition The point in the orbit of one component of a binary system which is farthest from the center of mass of the system.
	has participants binary star
	is an instance of binary star orbital event
apogalacticon	has antonym perigalacticon
	has definition The point in a star's orbit farthest from the Galactic center.
	is an instance of galaxy orbital event
apogee	has antonym perigee
	has definition The point at which a body in orbit around the Earth reaches its farthest distance from the Earth.
	is an instance of Earth orbital event
Apollo	has definition Prototype of a small group of asteroids whose orbits intersect that of Earth.
	has eccentricity e = 0.57
	has inclination i = 6°.4
	has orbital period P = 622d
	has semi-major axis a = 1.486 AU
	is a part of Apollo asteroid
	is an instance of Apollo asteroid
Apollo asteroid	has definition One of a small group of asteroids whose orbits intersect that of Earth. They are named for the prototype, Apollo.
	is a kind of Earth-crossing asteroid
	is a part of Earth-crossing asteroid
Apollo space program	has definition Successful US lunar exploration program in which the Apollo spacecraft 1 to 6 were unmanned; 7 to 10 were manned but did not land; and 11, 12 and 14 to 17 landed and returned safely. (Apollo 13 was an aborted mission.) The first men to land on the Moon were Neil Armstrong and Edwin Aldrin, from Apollo 11, on 20 July 1969. The final Apollo flight (17) lasted from 7 to 19 December 1972, and left a considerable quantity of exploratory devices on the lunar surface.
	is an instance of space science institution
apparent magnitude	has definition A measure of how bright a star looks in the sky. The brighter the star, the smaller the apparent magnitude. A star that is one magnitude brighter than another (e.g., +1 versus +2) looks 2.5 times brighter. The brightest star of all, of course, is the Sun, whose apparent magnitude is -26.74, followed by Sirius, whose apparent magnitude is -1.46, Canopus (-0.72), Alpha Centauri (-0.27), Arcturus (-0.04), and Vega (+0.03). Stars of the Big Dipper are fainter, most of them around magnitude +2. On a clear, dark night, the unaided eye can see stars as faint as apparent magnitude +6, and the largest telescopes penetrate to apparent magnitude +30.
	has definition Measure of the observed brightness of a celestial object as seen from the Earth. It is a function of the star's intrinsic brightness, its distance from the observer, and the amount of absorption by interstellar matter between the star and the observer. The mv, of Sun, -26.5 mag. A sixth-magnitude star is just barely visible to the naked eye.
	is a kind of magnitude
apsidal motion	has definition Rotation of the line of apsides in the plane of the orbit; (in a binary) precession of the line of apsides due to mutual tidal distortion.
	is an instance of precession
Apus	has acronym Aps
	has boundary
	has genitive Apodis
	has synonym Bird of Paradise
	is a part of celestial sphere
	is an instance of constellation named by Bayer
Aquarius	has acronym Aqr
	has boundary
	has genitive Aquarii
	has historical image
	has synonym Water Bearer
	is a part of Zodiac
	is an instance of zodiacal constellation
Aquila	has acronym Aql
	has boundary
	has genitive Aquilae
	has historical image
	has historical origin the eagle that belonged to Zeus. Aquila's most famous task was carrying the mortal Ganymede to the heavens to serve as Zeus' cup bearer
	has synonym Eagle
	is a part of celestial sphere
	is an instance of constellation
Ara	has acronym Ara
	has boundary
	has genitive Arae
	has historical origin the altar of the centaur Chiron or the altar that Noah built after the great flood
	has synonym Altar
	is a part of celestial sphere
	is an instance of constellation
arcminute	has definition A unit of angle equal to 1/60 of a degree.
	has equivalent 1/60 degree
	is an instance of angle unit
arcsecond	has definition One sixtieth of an arcminute, or 1/3600 of a degree.
	has equivalent 1/3600 degree
	has equivalent 1/60 arcminute
	is an instance of angle unit
Arcturus	has B-V magnitude 1.23
	has declination +19 10 57
	has definition A beautiful orange star that is the brightest in the constellation Bootes and the fourth brightest in the night sky. It lies 34 light-years away and is a member of the thick-disk population. Historically, Arcturus is famous because it was one of the first stars to have its proper motion measured.
	has definition An old subgiant disk star (K2 IIIp, mv = 0.06) about 11 pc distant.
	has right ascension 14 15 39.6
	has spectral type K1IIIbCN-1
	has synonym Alpha Boötis
	has synonym HR 5340
	has V magnitude -0.04
	is a part of Boötes
	is an instance of bright giant
	is an instance of K star
	is an instance of naked eye star
area	is a kind of quantity
area unit	has definition square meter
	has symbol m2
	is a kind of derived SI unit
Arecibo	has angular resolving power 5 arcminute
	has effective diameter 300 meters
	has position Puerto Rico
	has reference NAIC Arecibo Observatory
	is an instance of radio telescope
argon	has abundance 1 × 106 in Sun relative to H = 1 × 1012
	has abundance 1.2 p.p.m. in Earth's crust
	has abundance 9300 p.p.m. in atmopshere
	has atomic emission line 695.5431 nm for Ar I
	has atomic emission line 706.7218 nm for Ar I
	has atomic emission line 750.3869 nm for Ar I
	has atomic emission line 801.4786 nm for Ar I
	has atomic emission line 912.2967 nm for Ar I
	has atomic emission line 965.7786 nm for Ar I
	has atomic emission line 811.5311 nm for Ar I (strong)
	has atomic number 18
	has atomic radii 174 pm
	has biological role none
	has boiling point 87.29 K
	has chief source lquid air
	has critical pressure 4862 kPa
	has critical temperature 150.87 K
	has crystal cell dimension a = 531.088 pm
	has crystal type f.c.c
	has daily dietary intake very low
	has definition colourless, odourless gas comprising 1% of the atmosphere
	has density 1.784 kg m-3 for gas at 273 K
	has density 1380 kg m-3 for liquid at 87.29 K boiling point
	has density 1656 kg m-3 for solid at 40 K
	has discoverer Lord Rayleigh and Sir William Ramsay
	has discovery date 1894
	has discovery location London and Bristol, England
	has electron affinity -35 kJ mol-1 from Ar to Ar-
	has electron configuration [Ne]3s23p6 in ground state
	has hazard can asphyxiate if it excludes oxygen from the lungs
	has heat capacity 20.786 J K-1 mol-1 for gas at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 2.21 kJ mol-1
	has heat of vaporization 6.53 kJ mol-1
	has image
	has isotope mass range 32 to 46
	has lethal intake non-toxic
	has level in humans trace amounts in blood
	has mass absorption coefficient 123 cm2 g-1 for CuKα X-ray diffraction
	has mass absorption coefficient 13.5 cm2 g-1 for MoKα X-ray diffraction
	has mass magnetic susceptibility -6.16 × 10-9 kg-1 m3 for gas
	has mass of element in person very small for a 70 kg average person
	has melting point 83.78 K
	has mineral none
	has molar volume 24.12 cm3 at 40 K
	has name origin argos = inactive from Greek
	has neutron scattering length 0.1909 × 10-12 cm
	has number of isotopes 15
	has number of protons 18
	has ocean oxidation state 0
	has ocean residence time 28000 years
	has pronunciation ar-gon
	has registry number 7440-37-1 for Chemical Abstracts System database
	has relative atomic mass 39.948 in units of 12C = 12.000
	has reserves 6.6 × 1013 tonnes in atmosphere
	has space group Fm3m
	has specimen available in small pressurized canisters. Safe.
	has stable isotope argon 36
	has stable isotope argon 38
	has stable isotope argon 40
	has symbol Ar
	has synthesis mechanism extracted from the atmosphere by liquefaction
	has term symbol 1S0 in ground state
	has thermal conductivity 0.0177 W m-1 K-1 at 300 K for gas
	has thermal neutron capture cross section 0.675 barns
has toxic intake non-toxic
has uses inert atmosphere in lamps and high temperature metallurgy
has van der Waals radii 191 pm
has world production 700000 tonnes per year
is a kind of inert gas
is a kind of unclassified oceanic element
reacts with nothing
argon 36	has atomic mass 35.96754552
	has natural abundance 0.337 %
	has nuclear magnetic moment μ = 0
	has nuclear spin I = 0+
	has number of neutrons 18
	has number of nucleons 36
	has symbol 36Ar
	is an instance of argon
argon 37	has atomic mass 36.966776
	has decay mode EC (0.814 Mev)
	has decay mode no γ
	has half life 35.0 days
	has nuclear magnetic moment μ = +1.15
	has nuclear spin I = 3/2+
	has number of neutrons 19
	has number of nucleons 37
	has symbol 37Ar
	has uses research
	is an instance of argon
argon 38	has atomic mass 37.9627325
	has natural abundance 0.063 %
	has nuclear magnetic moment μ = 0
	has nuclear spin I = 0+
	has number of neutrons 20
	has number of nucleons 38
	has symbol 38Ar
	is an instance of argon
argon 39	has atomic mass 38.962
	has decay mode β- (0.565 Mev)
	has decay mode no γ
	has half life 268 years
	has nuclear magnetic moment μ = -1.3
	has nuclear spin I = 7/2-
	has number of neutrons 21
	has number of nucleons 39
	has symbol 39Ar
	is an instance of argon
argon 40	has atomic mass 39.9623837
	has natural abundance 99.600 %
	has nuclear magnetic moment μ = 0
	has nuclear spin I = 0+
	has number of neutrons 22
	has number of nucleons 40
	has symbol 40Ar
	is an instance of argon
argon 41	has atomic mass 40.964501
	has decay mode β- (2.492 Mev)
	has decay mode γ
	has half life 1.82 hours
	has nuclear spin I = 7/2-
	has number of neutrons 23
	has number of nucleons 41
	has symbol 41Ar
	is an instance of argon
argon 42	has atomic mass 41.963050
	has decay mode β- (0.60 Mev) %
	has decay mode no γ
	has half life 33 years
	has nuclear spin I = 0+
	has number of neutrons 24
	has number of nucleons 42
	has symbol 42Ar
	is an instance of argon
argon 44	has atomic mass 43.963650
	has decay mode β- (3.54 Mev)
	has decay mode γ
	has half life 11.87 minutes
	has nuclear spin I = 0+
	has number of neutrons 26
	has number of nucleons 44
	has symbol 44Ar
	is an instance of argon
argument of the perihelion	has definition An orbital element representing the longitude of the ascending node plus the angle along the orbit from the ascending node to the perihelion point.
	has definition Angular distance (measured in the plane of the object's orbit and in the direction of its motion) from the ascending node to the perihelion point.
	has symbol ω
	has synonym longitude of the perihelion
	is an instance of angle
	is an instance of orbital element
Ariel	has definition Second satellite of Uranus.
	has diameter 1600 km
	has discoverer Lassell
	has discovery date 1851
	has period 2.52 days
	is a part of Uranus
	is an instance of natural satellite
Aries	has acronym Ari
	has genitive Arietis
	has historical image
	has historical origin the ram sent by Hermes to carry the abused children of the King of Thessaly to safety
	has synonym Ram
	is a part of Zodiac
	is an instance of zodiacal constellation
Arietids	is an instance of meteor shower
Aristotelian physics	has definition Physics as promulgated by Aristotle; includes the hypothesis that our world is comprised of four elements, and that the universe beyond the moon is made of a fifth element and so is fundamentally different from the mundane realm.
	is a kind of outdated belief
array telescope	has definition a telescope composed of an array of separete individual elements acting in concert
	has element aperture
	has element separation
	has number of elements
	is a kind of electromagnetic telescope
arsenic	has abundance 1.45 × 10-3 p.p.m. in Atlantic surface seawater
	has abundance 1.45 × 10-3 p.p.m. in Pacific surface seawater
	has abundance 1.5 p.p.m. in Earth's crust
	has abundance 1.53 × 10-3 p.p.m. in deep Atlantic seawater
	has abundance 1.75 × 10-3 p.p.m. in deep Pacific seawater
	has abundance see list in Sun relative to H = 1 × 1012
	has appearance metallic for α form
	has atomic emission line 419.008 nm for As II
	has atomic emission line 445.847 nm for As II
	has atomic emission line 446.635 nm for As II
	has atomic emission line 449.423 nm for As II
	has atomic emission line 450.766 nm for As II
	has atomic emission line 454.348 nm for As II
	has atomic emission line 193.759 nm for As I (Strong, used in atom absorption spectrometry)
	has atomic number 33
	has atomic radii 125 pm
	has biological role essential to some species including humans
	has boiling point 889 K sublimes
	has chief source arsenopyrite, realgar and orpiment
	has covalent radii 121 pm
	has crystal cell dimension a = 376.0 pm for β form
	has crystal cell dimension a = 413.18 pm for α form
	has crystal cell dimension alpha angle = 54 deg 10' for α form
	has crystal cell dimension c = 10.548 pm for β form
	has crystal type hexagonal for β form
	has crystal type rhombohedral for α form
	has daily dietary intake 0.04 to 1.4 mg
	has definition a metalloid element with two main forms, grey α arsenic and β arsenic
	has density 4700 kg m-3 for solid at 293 K (β form)
	has density 5780 kg m-3 for solid at 293 K (α form)
	has discoverer Albertus Magnus
	has discovery date 1250
	has discovery location Germany
	has electrical resistivity 26 × 10-8 Ω m at 273 K
	has electron affinity 78 kJ mol-1 from As to As-
	has electron configuration [Ar]3d104s24p3 in ground state
	has electronegativity 2.18 Pauling
	has hardness brittle for α form
	has hazard salts and arsine gases are very poisonous. Stimulates metabolism in small doses, but it is carcinogenic and possibly teratogenic
	has heat capacity 20.786 J K-1 mol-1 for gas at constant pressure of 0.1 MPa at 298.15 K
	has heat capacity 24.64 J K-1 mol-1 for solid at constant pressure of 0.1 MPa at 298.15 K
	has heat of fusion 27.7 kJ mol-1
	has heat of vaporization 31.9 kJ mol-1
	has image
	has ionic radii 46 pm for As5+
	has ionic radii 69 pm for As3+
	has isotope mass range 67 to 87
	has lethal intake 50 to 300 mg
	has level in humans 0.0017 to 0.09 mg dm-3 in blood
	has level in humans 0.009 to 0.65 p.p.m. in muscle
	has level in humans 0.023 to 1.61 p.p.m. in liver
	has level in humans 0.08 to 1.6 p.p.m. in bone
	has linear expansion coefficient 4.6 × 10-6 K-1
	has main mining area not much mined as such because more than required is produced as a by-product of refining certain sulfide ores
	has mass absorption coefficient 69.7 cm2 g-1 for MoKα X-ray diffraction
	has mass absorption coefficient 83.4 cm2 g-1 for CuKα X-ray diffraction
	has mass magnetic susceptibility -3.97 × 10-9 kg-1 m3 for β form
	has mass magnetic susceptibility -9.17 × 10-10 kg-1 m3 for α form
	has mass of element in person 0.5 to 15 mg for a 70 kg average person depending on diet
	has melting point 1090 K for α form under pressure
	has mineral arsenopyrite, conichalcite, enargite, lollingite, olivenite, orpiment and realgar
	has molar volume 12.95 cm3 for α form
	has molar volume 15.9 cm3 for β form
	has name origin arsenikon = yellow orpiment from Greek
has neutron scattering length 0.658 × 10-12 cm
has number of isotopes 22
has number of protons 33
has ocean oxidation state V
has ocean residence time 90000 years
has pronunciation ahrs-nik
has registry number 7440-38-2 for Chemical Abstracts System database
has relative atomic mass 74.92159 in units of 12C = 12.000
has space group R3m for α form
has specimen available as powder. Danger !
has symbol As
has term symbol 4S3/2 in ground state
has thermal conductivity 50.0 W m-1 K-1 at 300 K for α form
has thermal neutron capture cross section 4.30 barns
has toxic intake 5 to 50 mg
has uses alloys, semiconductors, pesticides, wood preservatives and glass
has van der Waals radii 200 pm
has world production 47000 tonnes per year for As2O3
is a kind of group V element
is a kind of nonmetallic metalloid
is a kind of recycled oceanic element
reacts with hot acids and molten NaOH, tarnishes burns in oxygen
arsenic 71	has atomic mass 70.927114
	has decay mode β+ (2.013 Mev) 32%
	has decay mode γ
	has decay mode EC 68%
	has half life 2.72 days
	has nuclear magnetic moment μ = +1.6735
	has nuclear spin I = 5/2-
	has number of neutrons 38
	has number of nucleons 71
	has symbol 71As
	is an instance of arsenic
arsenic 72	has atomic mass 71.926755
	has decay mode β+ (4.355 Mev) 77%
	has decay mode γ
	has half life 26.0 hours
	has nuclear magnetic moment μ = -2.1566
	has nuclear spin I = 2-
	has number of neutrons 39
	has number of nucleons 72
	has symbol 72As
	is an instance of arsenic
arsenic 73	has atomic mass 72.923827
	has decay mode γ
	has decay mode EC (0.346 Mev)
	has half life 80.3 days
	has nuclear spin I = 3/2-
	has number of neutrons 40
	has number of nucleons 73
	has symbol 73As
	has uses research
	is an instance of arsenic
arsenic 74	has atomic mass 73.923827
	has decay mode β- (1.354 Mev)
	has decay mode β- (2.562 Mev) 31%
	has decay mode γ
	has decay mode EC 37%
	has nuclear magnetic moment μ = -1.597
	has nuclear spin I = 2-
	has number of neutrons 41
	has number of nucleons 74
	has symbol 74As
	is an instance of arsenic
arsenic 75	has atomic mass 74.9215942
	has magnetogyric ratio 4.5804 × 107 rad T-1 s-1
	has natural abundance 100%
	has NMR frequency 17.126 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 143 where 13C = 1.00
	has nuclear magnetic moment μ = +1.43947
	has nuclear quadrupole moment 0.314 × 10-28 m2
	has nuclear spin I = 3/2-
	has number of neutrons 42
	has number of nucleons 75
	has relative NMR sensitivity 0.0251 where 1H = 1.00
	has symbol 75As
	has uses Nuclear Magnetic Resonance
	is an instance of arsenic
arsenic 76	has atomic mass 75.922393
	has decay mode β- (2.97 Mev)
	has decay mode γ
	has half life 26.3 hours
	has nuclear magnetic moment μ = -0.906
	has nuclear spin I = 2-
	has number of neutrons 43
	has number of nucleons 76
	has symbol 76As
	is an instance of arsenic
arsenic 77	has atomic mass 76.920646
	has decay mode β- (0.6904 Mev)
	has decay mode γ
	has half life 38.8h
	has nuclear spin I = 3/2-
	has number of neutrons 44
	has number of nucleons 77
	has symbol 77As
	is an instance of arsenic
artifact	has creation date
	has creator
	has definition an object made by humans
	has owner
	has purpose
	is a kind of physical object
artificial satellite	has attitude control
	has definition a satellite made by humans which is gravitationaly bound and in orbit of a larger physical object
	has ground communication station
	has launch date
	has launch location
	has launch vehicle
	is a kind of instrument
	is a kind of satellite
	can have orbit decay date
AS Eri	has definition An eclipsing binary whose secondary is close to its Roche limit.
	is an instance of eclipsing binary
ascending node	has definition In the orbit of a solar-system body, the point where the body crosses the ecliptic from south to north: for a star, out of the plane of the sky toward the observer.
	is a kind of Sun orbital event
aspheric	has definition An optical surface with departures in shape from a perfect sphere in order to cancel optical imperfections or aberrations.
	has wavefront modification shape
	is a kind of wavefront modifier
association	has definition A sparsely populated grouping (mass range 102-103 Msun) of very young, massive stars lying along a spiral arm of the Milky Way, whose spectral types or motions in the sky indicate a common origin. The star density is insufficient for gravitation to hold the group together against shear by differential galactic rotation, but the stars have not yet had time to disperse completely. OB associations are composed of stars of spectral types O-B2; T associations have many young T Tauri stars. The internationally approved designation for associations is the name of the constellation followed by an arabic numeral - e.g., Perseus OB2.
	has most luminous member
	is a kind of collection of stars
astatine	has image
	is a kind of halogen
asterism	has definition a group of bright stars which form a conspicuous pattern on the celestial sphere
	has purpose to easily recognize a part of the sky
	is a part of constellation
	is an instance of equatorial sky area
asteroid	has asteroid number
	has definition A small planet-like body of the solar system, <e> ≃ 0.15, <i> ≃ 9°.7 . More than 1800 have been catalogued, and probably millions of smaller ones exist, but their total mass would probably be less than 3 percent that of the Moon. Their densities are poorly known (about 2.6 g cm-3), but they suggest a composition similar to carbonaceous chondrite. The bright asteroids are presumably original condensations and those fainter than about 14-15 mag are collision fragments. Asteroids and short-period comets have some orbital similarities. Also called minor planet
	has definition A small rocky body that orbits a star. In the solar system, most asteroids lie between the orbits of Mars and Jupiter. The largest asteroid is Ceres, about 900 kilometers in diameter.
	has definition Also called planetoids or minor planets, the asteroids are tiny planets most of which orbit the Sun between Mars and Jupiter. The largest - and the first discovered - is Ceres, with a diameter of 1,003 km. It is estimated that there may altogether be no fewer than 40000. A few have very elliptical orbits and cross the orbits of several other (major) planets. One or two even have their own satellites (moons).
	has synonym minor planet
	has synonym planetoid
	is a kind of celestial body
	is a part of our solar system
asteroid belt	has definition A region of space lying between Mars (1.5 AU) and Jupiter (5.2 AU), where the great majority of the asteroids are found. None of the belt asteroids have retrograde motion.
	has mean distance from Sun 1.5 to 5.2 AU
	is a kind of celestial body
	is a part of our solar system
asteroid impact	is a kind of impact event
astrology	has definition Divination using the positions of the planets, the Sun and the Moon as seen against the stars in the constellations of the zodiac - a "science" almost as old as homo sapiens. Although at one stage in history astrology and astronomy were almost synonymous- the latter has advanced so far during the last three centuries that the two now bear little relation to each other.
	has definition The belief that human affairs and people's personalities and characters are influenced by (or encoded in) the positions of the planets.
	is a kind of outdated belief
astrometric binary	is a kind of binary star
astrometry	has definition The branch of astronomy that deals with measuring the positions of celestial objects, especially stars. Astrometrists measure parallaxes and proper motions, which allow astronomers to determine the distances and velocities of the stars.
	is a kind of galactic astronomy
astronomer	has definition a scientist specializing in astronomy
	has domain astronomy
	is a kind of scientist
astronomical catalog	is a kind of data collection
astronomical constant	is a kind of constant
astronomical horizon event	has definition The time and azimuth at which a celestial body crosses the astronomical horizon of an oberver.
	is a kind of location dependent periodic celestial event
Astronomical Image Processing System	has acronym AIPS
	has definition Developed by the National Radio Astronomy Observatory.
	is a kind of astronomical software
astronomical institution	is a kind of institution
astronomical refraction	has definition The change in direction of travel (bending) of a light ray as it passes obliquely through the atmosphere. As a result of refraction, the observed altitude of a celestial object is greater than its geometric altitude. The amount of refraction depends on the altitude of the object and on atmospheric conditions.
	is a kind of refraction
astronomical software	is a kind of abstraction
astronomical unit	has definition Mean distance between the Earth and the Sun: 1.495985 × 1011 m.
	has definition The AU is the preferred unit for distances within the solar system. Mercury, the innermost planet, lies on average 0.39 AU from the Sun; Pluto, normally the farthest planet, lies on average 39.5 AU from the Sun.
	has definition The mean distance between the Earth and the Sun. The astronomical unit is defined as the length of the radius of the unperturbed circular orbit of a body of negligible mass moving around the Sun with a sidereal angular velocity of 0.017202098950 radian per day of 86400 ephemeris seconds. AU = 1.496 × 1013 cm ≈ 500 lt-sec.
	has definition The mean distance from the earth to the sun, equal to 92.81 million miles or 499.012 light-seconds.
	has definition The radius of a circular orbit in which a body of negligible mass, and free of perturbations, would revolve around the Sun in 2π / k days, where k is the Gaussian gravitational constant. This is slightly less than the semi-major axis of the Earth's orbit.
	has symbol AU
	has value in SI unit 1 au = 1.49598 × 1011 m, approximately
	is an instance of length unit
	is an instance of non SI unit
astronomy	has definition The science that studies the natural world beyond the earth.
	is a kind of science
astronomy theory	has domain astronomy
	is a kind of theory
Astrophysical Data Facility	has acronym ADF
	has definition Is responsible for designing, developing, and operating data systems that support the processing, management, archiving and distribution of NASA mission data. The ADF serves three broadly-defined astrophysics disciplines: high-energy astrophysics, UV/optical astrophysics, and infrared/submillimeter/radio astrophysics. The ADF collaborates with the GSFC Laboratory for High Energy Astrophysics (LHEA) and the Laboratory for Astronomy and Solar Physics (LASP) in managing data for specific missions. The ADF staff also support the astrophysics community's access to multi-mission and multi-spectral data archives in the National Space Science Data Center (NSSDC).
	has location Goddard Space Flight Center
	is an instance of database
Astrophysical Research Consortium Telescope	has altitude 2800 m
	has aperture 3.5 m
	has creation date 1994
	has focal ratio f/1.75
	has latitude 32° 47' N
	has location New Mexico, US
	has longitude 105° 49' W
	has mirror maker R. Angel, B. Martin
	has mirror type spin-cast borosilicate honey-comb
	has owner Apache Point
	has synonym ARC 3.5 m
	is an instance of altazimuth telescope
	is an instance of optical telescope
	is an instance of reflector
astrophysics	has definition The science that studies the physics and chemistry of extraterrestrial objects. The alliance of physics and astronomy, which began with the advent of spectroscopy, made it possible to investigate what celestial objects are and not just where they are.
	is a kind of physics
Astroweb	is an instance of database
asymptotic branch star	has definition Globular cluster stars, which are found in that part of the HR diagram that connects the top pf the giant tip with the horizontal branch stars.
	is a kind of star
atmophile element	has definition volatile element that tends to be found in the atmosphere of a planet or asteroid
	has occurrence atmosphere of a planet or asteroid
	is a kind of planetary element
atmosphere	has composition 78% nitrogen and 21% oxygen (with 1% of other gases) by volume
	has definition A unit of pressure.
	has definition Mantle of gases round a star planet or moon, sometimes even forming the apparent surface of the body. For a body to retain an atmosphere depends on the body's gravity, and the temperature and composition of the gases. Mean atmospheric pressure at the surface is 10330 kg/m2, and is also referred to as atmosphere.
	has equivalent 1.013 bars
	has equivalent 101325 pascals
	has equivalent 14.07 lb in-2
	has equivalent 760 torr
	is a part of Earth
	is an instance of pressure unit
atmospheric dispersion corrector	has definition An optical device usually comprising two thin prisms which can rotate to compensate for the elongation of a star image caused by the wavelength dependence of the refractive index of air.
	has wavefront modification wavelength
	is a kind of wavefront modifier
atmospheric extinction	has definition Decrease in the intensity of light from a celestial body due to absorption and scattering by the Earth's atmosphere. The extinction increases from the zenith to the horizon and affects short wavelengths more than long wavelengths, so that objects near the horizon appear redder than they are at the zenith.
	is a kind of selective absorption
atomic constant	is a kind of fundamental physical constant
atomic mass constant	has approval date 1961
	has definition One-twelfth the mean mass of an atom of carbon 12 (including the orbital electrons).
	has equation
	has symbol mu
	has uncertainty 0.00000013 × 10-27 kg
	has unit kg
	has value 1.66053873 × 10-27 kg
	is an instance of mass
	is an instance of physico chemical constant
atomic mass number	has definition The total number of protons and neutrons in an atom's nucleus. For example, oxygen-16 has a mass number of sixteen, because it has eight protons and eight neutrons.
	is an instance of integer
	is an instance of quantum quantity
atomic mass unit	has approval agency International Union of Pure and Applied Physics
	has approval date 1960
	has definition The masses of atoms and molecules are generally given in atomic mass units. These units are based on a scale in which the mass of carbon 12 is taken to be 12. Atomic masses were originally given as atomic weights on a scale where the mass of the hydrogen atom was unity, later they were based on oxygen or oxygen 16; these scales have all been replaced by the carbon 12 scale.
	has equivalent 1.6605402 × 10-27 kg
	has proposal date 1959
	has symbol u
	has synonym dalton
	is a unit of mass
	is an instance of mass unit
atomic number	has definition The number of protons in an atom's nucleus. This determines the type of element.
	has proposal date 1865
	has range 1 to 103
	has synonym charge number
	is an instance of integer
	is an instance of quantum quantity
	was proposed by J. A. R. Newlands
atomic process	has domain atomic physics
	is a kind of event
	is a kind of physical process
attenuation	has definition The falling off of the energy density of radiation with distance from the source, or with passage through an absorbing or scattering medium.
	is a kind of absorption
atto	has symbol a
	has value 10-18
	is an instance of unit prefix
Auger transition	has definition A radiationless quantum jump that occurs in the X-ray region. When a K-electron is removed from an atom and an L-electron drops into the vacancy in the K-shell, the energy released in the latter transition goes not into radiation, but into the liberation of one of the remaining L-electrons.
	is a kind of ionization
Auriga	has acronym Aur
	has boundary
	has genitive Aurigae
	has historical image
	has historical origin Erechtheus, the charioteer (son of Hephaestus) is carying two to three children on his arm
	has synonym Charioteer
	is a part of celestial sphere
	is an instance of constellation
aurora	has definition Light radiated by ions in the Earth's atmosphere, mainly near the geomagnetic poles, stimulated by bombardment by energetic particles ejected from the Sun (see solar wind). Aurorae appear about 2 days after a solar flare and reach their peak about 2 years after sunspot maximum.
	has definition Spectacular array of light in the night sky, caused by charged particles from the Sun hitting the Earth's upper atmosphere. The aurora borealis is seen in the north of the Northern hemisphere; the aurora australis in the south of the Southern.
	has definition the light produced by excited atoms and ions in the upper atmosphere of a planet
	has location the ionosphere in the polar regions of a planet
	is a kind of celestial event
	is a part of ionosphere
aurora australis	has definition an aurora ocurring in the southern hemisphere of the Earth
	has location southern hemisphere
	is a kind of aurora
aurora borealis	has definition an aurora ocurring in the northern hemisphere of the Earth
	has location northern hemisphere
	is a kind of aurora
autoionization	has definition A phenomenon occurring when a discrete double-excitation state of an atom lies in the ground-state continuum. In the autoionization process one of the excited electrons is ejected, leaving the ion in an excited state (see dielectronic recombination; see also Auger effect). (also called pre-ionization)
	has inverse process dielectronic recombination
	is a kind of ionization
autumnal equinox	has definition See equinox
	is an instance of equinox
Avogadro number	has definition The number of atoms in 12 grams of carbon 12. The number of atoms in a gram-atom (mass in grams numerically equal to the atomic weight) or the number of molecules in a gram-molecule (mass in grams numerically equal to the molecular weight).
	has symbol NA
	has uncertainty 0.00000047 × 1023 mol-1
	has value 6.02214199 × 1023 mol-1
	is an instance of physico chemical constant
	is named after Amadeo Avogadro
axion	has definition A hypothetical spin-0 particle with a very small mass of 10-5-10-3 eV. It was postulated in order to provide a natural solution to the "strong CP problem".
	has mass 10-5 to 10-3 eV
	has spin 0
	is a kind of boson
	is a kind of hypothetical particle
axis	has definition Theoretical straight line through a celestial body, around which it rotates.
	is a kind of line
axis motion	has definition the motion of the axis of a system
	is a kind of motion
axisymmetric collapse	has definition Collapse of mass in such a way that the mass maintains the symmetry of a cylinder.
	has symmetry cylindrical
	is a kind of collapse
azimuth	has definition Angular distance from the north point eastward to the intersection of the celestial horizon with the vertical circle passing through the object and the zenith.
	has definition Directional bearing around the horizon, measured in degrees from north (0°).
	is an instance of angle
	is an instance of local coordinate component
azimuthal quantum number	has definition A measure of the minor axis of an elliptic orbital of an electron according to the Bohr-Sommerfeld theory.
	has symbol k
	is an instance of quantum quantity
B band	has definition Telluric lines due to O2 absorption in Earth's atmosphere, but originally thought to originate in the Sun by Fraunhofer.
	has species O2
	has wavelength 7100 Å
	is a kind of Fraunhofer line
	is a kind of molecular band
	occurs in Earth's atmosphere
B ring	is a kind of ring
	is a part of Saturn ring system
B star	has absorption line He I
	has color blue-white
	has definition Blue-white star of spectral type B whose spectra are characterized by absorption lines of neutral helium which reach their maximum intensity at B2. The Balmer lines of hydrogen are strong, and lines of singly ionized oxygen and other gases are also present.
	has surface temperature 11000 to 28000 K
	is a kind of early star
b-lines	has definition A triplet of spectral lines of Mg I.
	has wavelength λλ 5167-5184 Å
	is a kind of absorption line
B[e] star	has definition Be stars exhibiting forbidden lines in emission. [JJ95]
	has emission line forbidden lines
	is a kind of Be star
Baade's Window	has definition A clearing in the dust clouds of the constellation Sagittarius where astronomers can view stars in the Galactic bulge. Baade's window lies four degrees south of the Galactic center, so an observer's line of sight passes within 1800 light-years of the Milky Way's center.
	is a part of celestial sphere
	is an instance of equatorial sky area
backscatter	has definition Scattering of radiation (or particles) through angles greater than 90° with respect to the original direction of motion.
	is a kind of scattering
Bahcall-Soneira Model	has definition A model for the Galaxy first published by John Bahcall and Raymond Soneira in 1980. In its original form, it sought to reproduce star counts in different parts of the sky by employing only a (thin) disk and a halo; it had no thick disk.
	is a kind of galaxy theory
Bailey type	has definition A classification of RR Lyrae stars according to the shape and amplitude of their light variation
	is a kind of RR Lyrae star
Baily's beads	has definition Small "beads" of sunlight which shine through the valleys on the limb of the Moon in the instant before (or after) totality in a total solar eclipse.
	has discoverer Francis Baily
	has discovery date 1836
	has synonym diamond ring effect
	is an instance of solar eclipse
Baldet-Johnson band	has species CO+ radical
	is a kind of molecular band
Ballik-Ramsay band	has wavelength 1.7625 μ (transition 0-0)
	is a kind of C2 band
Balmer jump	has definition The sudden decrease in the intensity of the continuous spectrum at the limit of the Balmer series of hydrogen at 3646 Å, representing the energy absorbed when electrons originally in the second energy level are ionized.
	has species hydrogen (H I)
	has synonym Balmer discontinuity
	has wavelength 3646 Å
	is a kind of absorption edge
Balmer line	has definition The series lies in the visible portion of the spectrum. (Deuterium Hα is 1.785 Å short-ward of hydrogen Hα)
	has lower energy level 2
	has series limit 3647 Å
	is a kind of hydrogen line
	is a kind of spectral series line
Bamberga	has absolute magnitude +8.14
	has albedo < 0.05
	has asteroid number 324
	has definition Asteroid with the darkest known surfaces in the solar system, the only minor planet known to have such a low albedo.
	has eccentricity e = 0.36,
	has inclination i = 11°.2
	has mean opposition magnitude +11.41
	has meteorite class carbonaceous chondrite
	has radius larger than Pallas
	has rotation period 8h< sup> -has source: [H76]
	has semi-major axis a = 2.80 AU,
	is a part of asteroid belt
	is an instance of asteroid
band head	has definition The conspicuous sharp boundary which usually occurs at the head of a molecular band and which fades gradually toward either longer or shorter wavelengths, depending on the quadratic relation between frequency and rotational quantum number.
	is a kind of set of molecular lines
bar	has definition An absolute unit of pressure equal to 106 dyn cm-2.
	is an instance of CGS unit
	is an instance of pressure unit
barium	has image
	has ocean oxidation state II
	has ocean residence time 10000 years
	is a kind of alkali earth metal
	is a kind of recycled oceanic element
barium star	has definition Late type giants (G2 to K4) with a very strong BaII 4554 line. Main sequence stars with strong BaII lines have also been discovered recently.
	has definition Peculiar low-velocity, strong lined red-giant stars of spectral types G, K, and M, with abnormally large abundances of heavy s-process (but not r-process) elements. They are usually regarded as old disk stars of ~ 1-2 Msun.
	has synonym Ba II star
	has synonym Ba star
	is a kind of heavy-metal star
Barnard's star	has definition A faint binary star with the second largest proper motion known. Long-term observations of its light curve suggest a possible third component with a mass about 1.2 that of Jupiter, although this observation has been challenged.
	has discoverer Edward Emerson Barnard
	has discovery date 1916
	has distance 1.83 pc
	has orbital period 25 years
	has proper motion 10.25 arcseconds per year
	has radial velocity 100 km/sec
	has spectral type M5 V
	is a part of Ophiuchus
	is an instance of binary star
	is an instance of M star
	is an instance of red dwarf
barotropic gas	has definition A gas in which the pressure is a function of the density only.
	is a kind of gas
barred spiral	has abundance 20% of spiral galaxies are barred spiral
	has definition (in Hubble's (1936) classification, SB: in Morgan's classification, B) A spiral galaxy whose nucleus is in the shape of a bar, at the ends of which the spiral arms start.
	is a kind of spiral galaxy
baryon	has definition Heavy subatomic particle composed of 3 quarks.
	has number of quarks 3
	has spin 1/2 or 3/2
	is a kind of fermion
	is a kind of fermion
	is a kind of hadron
base SI unit	has definition a unit assumed to be mutually independent from which all other units are derived
	is a kind of SI unit
Be star	has definition Irregular variables of spectral type B (or occasionally O or A) with hydrogen emission lines in their spectra. The Be phenomenon involves rapid stellar rotation, circumstellar shells, and mass loss.
	has definition Non-supergiant B-type stars, which have shown emission in at least one of the Balmer lines at some time.
	has emission line at least one of the Balmer lines at some time
	is a kind of B star
	is a kind of emission line star
	is a kind of variable
Beacon explorer A	is an instance of inflatable spacecraft
Beacon satellite	is a kind of inflatable spacecraft
beat Cepheid	has definition Dwarf Cepheid in which two or more almost identical periods exist which cause periodic amplitude fluctuations in their light curves. The "beat" period averages about 2 to 21/2 hours.
	is a kind of dwarf Cepheid
becquerel	has approval agency 15th CGPM
	has approval date May 1975
	has base unit s-1
	has definition Unit of radioactivity; 1 becquerel represents one disintegration, or other nuclear transformation, per second.
	has equivalent 2.703 × 10-11 curies
	has symbol Bq
	is an instance of named derived SI unit
	is an instance of radioactivity unit
	is named after A. H. Becquerel
bel	has symbol B
	has value in SI unit (1/2) ln 10 Np
	is an instance of non SI unit
belief	is a kind of abstraction
Bellatrix	has definition A B2 III star.
	has distance 80 pc
	has spectral type B2 III
	has synonym gamma Orionis
	is an instance of B star
	is an instance of giant
Bent-yoke equatorial telescope	has mounting bent-yoke equatorial
	is a kind of equatorial telescope
berkelium	has image
	is a kind of transuranium element
beryllium	has abundance 14 in Sun relative to H = 1 × 1012
	has abundance 17.5 × 10-8 p.p.m. in deep Atlantic seawater
	has abundance 2.6 p.p.m. in Earth's crust
	has abundance 22 × 10-8 p.p.m. in deep Pacific seawater
	has abundance 3.5 × 10-8 p.p.m. in Pacific surface seawater
	has abundance 8.8 × 10-8 p.p.m. in Atlantic surface seawater
	has atomic emission line 234.861 nm for Be I (used in atom absorption spectrometry)
	has atomic emission line 381.345 nm for Be I
	has atomic emission line 436.099 nm for Be II
	has atomic emission line 467.333 nm for Be II
	has atomic emission line 527.081 nm for Be II
	has atomic emission line 467.342 nm for Be II (strong)
	has atomic number 4
	has atomic radii 113 pm
	has biological role none
	has boiling point 3243 K under pressure
	has bulk modulus 110 GPa
	has chief source beryl, bertrandite
	has covalent radii 89 pm
	has crystal cell dimension a = 228.55, c = 358.32 pm for α-Be
	has crystal cell dimension a = 255.15 pm for β-Be
	has crystal type b.c.c. for β-Be
	has crystal type h.c.p. for α-Be
	has daily dietary intake 0.01 mg
	has definition Silvery-white, lustrous, relatively soft metal which is unaffected by air or water, even at red heat. Rare and fragile element. Nuclear reactions in stars destroy it. Most and possibly all beryllium originated when cosmic rays smashed into heavier atoms in space and split them into lighter ones, such as beryllium.
	has density 1847.7 kg m-3 for solid at 293 K
	has discoverer Nicholas Louis Vauquelin
	has discovery date 1797
	has discovery location Paris, France
	has electrical resistivity 4.0 × 10-8 Ω m at 293 K
	has electron affinity -18 kJ mol-1 from Be to Be-
	has electron configuration [He]2s2 in ground state
	has electronegativity 1.57 Pauling
	has hazard deadly poison, carcinogenic for lab animals and maybe for humans
	has hazard inhalation of dust causes severe and irreparable lung damage
	has heat capacity 16.44 J K-1 mol-1 for solid at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 20.786 J K-1 mol-1 for gas at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 9.80 kJ mol-1
	has heat of vaporization 308.8 kJ mol-1
	has image
	has ionic radii 34 pm for Be+
	has isotope mass range 6 to 11
	has lethal intake 317 mg kg-1 acetate in rat
	has level in humans < 1 × 10-5 mg dm-3 in blood
	has level in humans 0.00075 p.p.m. in muscle
	has level in humans 0.0016 p.p.m. in liver
	has level in humans 0.003 p.p.m. in bone
	has linear expansion coefficient 11.5 × 10-6 K-1
	has longest lived isotope beryllium 9
	has main mining area Brazil, USA, Madagascar, Germany, Czech Republic, Russia, India
	has mass absorption coefficient cm2 g-1 0.298 for MoKalpha X-ray diffraction
	has mass absorption coefficient cm2 g-1 1.50 for CuKalpha X-ray diffraction
	has mass magnetic susceptibility -1.3 × 10-8 kg-1 m3 for solid
	has mass of element in person 0.036 mg for a 70 kg average person
	has melting point 1551 ± 5 K
	has mineral beryl, bertrandite, chrysoberyl, gadolinite, herderite
	has molar volume 4.88 cm3
	has name origin beryllos = beryl from Greek
	has neutron scattering length 0.779 × 10-12 cm
	has number of isotopes 6 including nuclear isomers
	has number of protons 4
	has ocean oxidation state II
	has ocean residence time 4000 years
	has poisson's ratio 0.02 GPa
has pronunciation be-ril-iuhm
has registry number 7440-41-7 for Chemical Abstracts System database
has relative atomic mass 9.012182 in units of 12C = 12.000
has reserves 400000 tonnes
has rigidity modulus 156 GPa
has space group Im3m for β-Be
has space group P63/mmc for α-Be
has specimen lumps, powder. Danger !
has symbol Be
has synthesis mechanism electrolysis of fused BeCl2
has term symbol 1S0 in ground state
has thermal conductivity 200 W m-1 K-1 at 300 K
has thermal neutron capture cross section 0.0092 barns
has toxic intake 13 mg kg-1 in rat
has uses alloys with copper and nickel increases electrical and thermal conductivities
has uses copper alloys used to make spark proof tools
has world production 364 tonnes year-1
has young's modulus 318 GPa
is a kind of alkali earth metal
is a kind of light element
is a kind of recycled oceanic element
beryllium 10	has atomic mass 10.013534
	has decay mode β- (0.5561 Mev)
	has decay mode no γ
	has half life 1.52 × 106 years
	has nuclear spin I = 0+ h/2π
	has number of neutrons 6
	has number of nucleons 10
	has symbol 10Be
	has uses research
	is an instance of beryllium
beryllium 11	has atomic mass 11.021658
	has decay mode α (11.48 Mev)
	has decay mode β-
	has decay mode γ
	has half life 13.8 seconds
	has nuclear spin I = 1/2+ h/2π
	has number of neutrons 7
	has number of nucleons 11
	has symbol 11Be
	is an instance of beryllium
beryllium 12	has atomic mass 12.02692
	has decay mode β- (11.71 Mev)
	has decay mode n
	has half life 2.4 × 10-2 seconds
	has nuclear spin I = 0+ h/2π
	has number of neutrons 8
	has number of nucleons 12
	has symbol 12Be
	is an instance of beryllium
beryllium 14	has atomic mass 13.0375
	has decay mode β- (16.4 Mev)
	has half life 4 × 10-3 seconds
	has nuclear spin I = 0+ h/2π
	has number of neutrons 10
	has number of nucleons 14
	has symbol 14Be
	is an instance of beryllium
beryllium 6	has atomic mass 6.019725
	has decay mode 2p.α
	has half life 5.9 × 10-21 seconds
	has nuclear spin I = 0+ h/2π
	has number of neutrons 2
	has number of nucleons 6
	has symbol 6Be
	is an instance of beryllium
beryllium 7	has atomic mass 7.016928
	has decay mode γ
	has decay mode EC (0.862 Mev)
	has half life 53.82 days
	has nuclear spin I = 3/2+ h/2π
	has number of neutrons 3
	has number of nucleons 7
	has symbol 7Be
	has uses research
	is an instance of beryllium
beryllium 8	has atomic mass 8.005305
	has decay mode 2α (0.046 Mev)
	has decay mode no γ
	has half life 7 × 10-17 seconds
	has nuclear spin I = 0+ h/2π
	has number of neutrons 4
	has number of nucleons 8
	has symbol 8Be
	is an instance of beryllium
beryllium 9	has atomic mass 9.0121822
	has magnetogyric ratio 3.7589 × 107 rad T-1 s-1
	has natural abundance 100%
	has NMR frequency 14.053 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 78.8 where 13C = 1.00
	has nuclear magnetic moment μ = -1.1779 nuclear magnetons with diamagnetic correction
	has nuclear quadrupole moment 0.05288 × 10-28 m2
	has nuclear spin I = 3/2- h/2π
	has number of neutrons 5
	has number of nucleons 9
	has relative NMR sensitivity 1.39 × 10-2 where 1H = 1.00
	has symbol 9Be
	has uses Nuclear Magnetic Resonance
	is an instance of beryllium
Besselian element	has definition One of several quantities tabulated for the calculation of accurate predictions of an eclipse or occultation for any point on or above the surface of the Earth.
	is a kind of orbital quantity
Besselian year	has definition The period of one complete revolution in right ascension of the fictitious mean sun, as defined by Newcomb. The beginning of a Besselian year, traditionally used as as standard epoch, is denoted by the suffix ".0". Since 1984 standard epochs have been defined by the Julian year rather that the Besselian year. For distinction, the beginning of the Besselian year is now identified by the prefix B (e.g., B1950.0).
	is an instance of year
Beta Aquarii	has B-V magnitude 0.83
	has declination -05 34 16
	has right ascension 21 31 33.4
	has spectral type G0Ib
	has synonym HR 8232
	has V magnitude 2.91
	is a part of Aquarius
	is an instance of naked eye star
	is an instance of yellow supergiant
Beta Arae	has B-V magnitude 1.46
	has declination -55 31 47
	has right ascension 17 25 17.9
	has spectral type K3Ib-IIa
	has synonym HR 6461
	has V magnitude 2.85
	is a part of Ara
	is an instance of K star
	is an instance of naked eye star
	is an instance of supergiant
Beta Camelopardalis	has B-V magnitude 0.92
	has declination +60 26 32
	has right ascension 05 03 25.1
	has spectral type G0Ib
	has synonym HR 1603
	has V magnitude 4.03
	is a part of Camelopardalis
	is an instance of naked eye star
	is an instance of yellow supergiant
Beta Cancri	has B-V magnitude 1.48
	has declination + 9 11 8
	has right ascension 8 16 30.9
	has spectral type K4IIIBa0.5
	has synonym HR 3249
	has V magnitude 3.52
	is a part of Cancer
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Beta Cephei	is a part of Cepheus
	is an instance of beta Cephei star
beta Cephei star	has definition A small group of short-period pulsating variables lying slightly above the upper main sequence. They have a doubly periodic light curve, and are confined within a narrow band of the H-R diagram which lies near the end of core hydrogen-burning stars of roughly 10-20 Msun. beta Cephei itself has at least three components.
	has period P = 3.5 to 6 hr
	has prototype beta Cephei
	has spectral type O9-B3
	has synonym beta Canis Majoris star
	is a kind of periodic variable
Beta Ceti	has B-V magnitude 1.02
	has declination -17 59 12
	has right ascension 0 43 35.3
	has spectral type K0IIICH-1H,K-0
	has synonym HR 188
	has V magnitude 2.04
	is a part of Cetus
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Beta Crucis	has B-V magnitude -0.23
	has declination -59 41 19
	has right ascension 12 47 43.3
	has spectral type B0.5III
	has synonym HR 4853
	has V magnitude 1.25
	is a part of Crux
	is an instance of B star
	is an instance of giant
	is an instance of naked eye star
Beta Delphini	has B-V magnitude 0.44
	has declination +14 35 43
	has right ascension 20 37 32.9
	has spectral type F5IV
	has synonym HR 7882
	has V magnitude 3.63
	is a part of Delphinus
	is an instance of F star
	is an instance of naked eye star
	is an instance of subgiant
Beta Herculis	has B-V magnitude 0.94
	has declination +21 29 22
	has right ascension 16 30 13.1
	has spectral type G7IIIa
	has synonym HR 6148
	has V magnitude 2.77
	is a part of Hercules
	is an instance of G star
	is an instance of giant
	is an instance of naked eye star
Beta Hydri	has B-V magnitude 0.62
	has declination -77 15 16
	has right ascension 0 25 45.3
	has spectral type G2IV
	has synonym HR 98
	has V magnitude 2.80
	is a part of Hydrus
	is an instance of G star
	is an instance of naked eye star
	is an instance of subgiant
Beta Librae	has B-V magnitude -0.11
	has declination -9 22 59
	has right ascension 15 17 0.3
	has spectral type B8V
	has synonym HR 5685
	has V magnitude 2.61
	is a part of Libra
	is an instance of B star
	is an instance of dwarf
	is an instance of naked eye star
beta Lyrae star	has definition A class of eclipsing binary whose secondary minima are intermediate between those of Algol and those of W UMa. The prototype beta Lyr (B8.5 II, F V) is a complex eclipsing system and is presently in a state of rapid mass transfer. The spectrum of one companion is invisible; it may be a black hole. Beta Lyrae is also a weak radio source.
	is a kind of eclipsing binary
beta Persei star	has definition A class of eclipsing binary (see Algol) with periods of from 2 to 5 days, the depth of whose secondary minimum is almost negligible.
	has prototype Algol
	is a kind of eclipsing binary
Beta Pictoris	has distance 50 light years
	has image
	is a part of Pictor
	is an instance of star
Beta Trianguli	has B-V magnitude 0.14
	has declination +34 59 14
	has right ascension 2 9 32.5
	has spectral type A5II
	has synonym HR 622
	has V magnitude 3.00
	is a part of Triangulum
	is an instance of A star
	is an instance of bright giant
	is an instance of naked eye star
Beta Volantis	has B-V magnitude 1.13
	has declination -66 8 13
	has right ascension 8 25 44.3
	has spectral type K1III
	has synonym HR 3347
	has V magnitude 3.77
	is a part of Volans
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
beta-decay	has definition Emission of an electron and an antineutrino (or a positron and a neutrino) by a radioactive nucleus by any one of several processes. e.g., the spontaneous β-decay of a free neutron (n → p + e- + ν bar). The A-number is unchanged, but the Z-number is increased (or decreased) by 1. Beta-decay is a so-called weak interaction. Since electrons of all energies (up to a certain maximum) are emitted in β-decay, this process exhibits a continuous spectrum (unlike α-particle emission, which exhibits a line spectrum).
	has definition Spontaneous emission by a heavier element (such as uranium) of negatively charged electrons - beta particles. The result of this radioactive decay is that the original element is very gradually converted into another element. Beta particle emission may be simultaneous with alpha particle decay.
	has definition The disintegration of an atomic nucleus, in which an electron (which was historically called a beta particle) and an antineutrino are emitted. Since the electron carries away one unit of negative charge, the final nucleus has a charge one greater than the initial nucleus.
	has definition The process in which a neutron disintegrates into a proton, an electron, and an antineutrino. The escaping electron is sometimes called a beta ray. (See neutrino; neutron; proton.)
	is a kind of nuclear decay
beta-particle	has definition An electron or a positron emitted from an excited nucleus when it returns to its ground state via β-decay.
	has definition Particles first discovered in radioactive β decay - later identified as electrons.
	is a kind of electron
Betelgeuse	has definition A red semiregular variable supergiant. Betelgeuse is also a strong infrared emitter - at 2 µ the brightest in the sky.
	has definition A red supergiant star in the constellation Orion and the brightest red supergiant in Earth's sky.
	has distance 500 pc
	has image
	has spectral type M2 Iab
	has synonym alpha Ori
	is an instance of red supergiant
	is an instance of semiregular variable
biased galaxy formation	has definition The theory that bright galaxies form preferentially from anomalously overdense perturbations in the early universe.
	is a kind of galaxy theory
big bang	has antonym big crunch
	has definition A general class of cosmological models that assume the universe is homogeneous and isotropic on large scales and that allow the universe to evolve in time. Most calculation in the standard big bang model assume a Friedmann cosmology. (See Friedmann equation; homogeneity; isotropy.) A cosmological model that has the same properties as a Friedmann model under some conditions is said to have a Friedmann limit.
	has definition A homogeneous, isotropic model of the Universe involving nonstatic (i.e., expanding or contracting) solutions to Einstein's field equations (with zero cosmological constant) calculated by the Russian mathematician A. Friedmann in 1922.
	has definition A model of the Universe which started with an initial singularity. The Friedmann model of a homogeneous, isotropic universe (composed of adiabatically expanding matter and radiation, as a result of a primeval explosion) is the standard example.
	has definition According to standard cosmology, the explosion that started the universe expanding 10 to 15 billion years ago.
	has definition An evolutionary model of cosmology in which the universe began about 10 billion years ago, in a state of extremely high density and temperature. According to this model, the universe has been expanding, thinning out, and cooling since its beginning. It is an observational fact that distant galaxies are all moving away from our own galaxy, as predicted by the big bang model. (See closed universe; flat universe; Friedmann models; open universe.)
	has definition Model of cosmic history in which the universe begins in a state of high density and temperature, both of which decrease as the universe expands. Less a theory than a school of theories that attempt to trace how the universe evolved.
	has definition One of three standard Big Bang models that were formulated by Friedmann and Lemaitre of an isotropic and homogeneous universe composed of expanding matter and radiation. In these models space is unbounded.
	has definition The initial point of creation.
	has definition The most widely accepted theory of the origin of the Universe. It asserts that the Universe began some 1010 years ago from a space-time point of infinite energy density (a singularity). The expansion of the Universe since that time is akin to the expansion of the surface of an inflating balloon: every point on the balloon's surface is moving away from every other point. So, microbes living on the surface see their two-dimensional world expanding, yet there is no center to the expansion which is everywhere uniform.
	has definition The state of extremely high (classically, infinite) density and temperature from which the universe began expanding.
	has definition Theory originally proposed by Georges Lemaitre but elaborated by George Gamow and the α-β-hypothesis-γ that the Universe began with the Big Bang, the superexplosion of all the matter now dispersing in the Universe. Since the nuclear physics involved has been explained, and various supporting evidence - notably helium abundance and the sources of radio emission - has been discovered, the theory is almost universally accepted (although at one time the steady state theory rivaled it in popularity).
	has synonym Friedmann-Lemaitre universe
	is a kind of cosmology theory
Big bang crossover effect	has definition The epoch during the radiation era when the universe switched from being radiation-dominated to being matter-dominated.
	has start time 1012 s
	is a kind of Big Bang era
Big Bang era	has definition A theoretical era postulated to have occurred after the Big Bang. They are in order : Planck era hadron era inflation era lepton era nucleosynthetic era radiation era matter era
	has start time relative to the Big Bang
	has temperature
	is a kind of era
	is followed by
	is preceded by
big crunch	has antonym big bang
	has definition If the universe has a mass density exceeding the critical mass density, then gravity will eventually reverse the expansion, causing the universe to recollapse into what is often called the big crunch. See also closed universe.
	has definition One hypothesized future for the universe in which the current expansion stops, reverses, and results in all space and all matter collapsing together; a reversal of the big bang.
	has definition The state of extremely high density and temperature into which a closed universe will recollapse in the distant future.
	is a kind of cosmology theory
binary galaxy	has definition Two galaxies orbiting each other owing to their mutual gravitational attraction.
	has number of galaxies 2
	has synonym double galaxy
	is a kind of collection of galaxies
binary pulsar	is a kind of pulsar
binary star	has definition A system of two stars orbiting around a common center of gravity. Visual binaries are those whose components can be resolved telescopically (i.e., angular separation > 0'.5) and which have detectable orbital motion. Astrometric binaries are those whose dual nature can be deduced from their variable proper motion; spectroscopic binaries, those whose dual nature can be deduced from their variable radial velocity. At least half of the stars in the solar neighborhood are members of binary (or multiple) systems. (See photometric binaries; optical pairs.)
	has number of stars 2
	has orbital period
	is a kind of star
	is a kind of star system
binary star orbital event	is a kind of orbital event
binding energy	has definition The energy required to break up a system. In particular, the binding energy of an atomic nucleus is the energy released in the formation of the nucleus. The most strongly bound nuclei are those with atomic weights between about 50 and 65 (the iron group). Lighter nuclei are less strongly bound because of their larger surface-to-volume ratios; heavier nuclei, because the effects of Coulomb repulsion increase with the nuclear charge.
	is a kind of energy
biochemical process	is a kind of biological process
	is a kind of chemical process
biological process	has domain biology
	is a kind of process
biology	has definition The scientific study of life and living matter.
	is a kind of science
bismuth	has image
	has ocean oxidation state III
	is a kind of group V element
	is a kind of metallic element
	is a kind of scavenged oceanic element
BL Lacertae	has definition A highly variable object (the most rapid radio variable known, also an optically violent variable - mv = 12 to 15 mag - and an infrared source). Probably an exceedingly compact nonthermal object, and undoubtedly extragalactic. Its optical spectrum is characterized by an absence of lines, so its redshift cannot be measured. (In 1974 Oke and Gunn infer z = 0.07 from an Hβ absorption line in the surrounding halo and conclude that it lies at the center of a bright (Mv = - 23) elliptical. If true, this would make BL Lac the nearest known quasar.)
	has definition A member of a class of astronomical objects with the following characteristics: (1) rapid variations in intensity at radio, infrared, and optical wavelengths; (2) energy distributions such that most of the energy is emitted at infrared wavelengths; (3) absence of discrete features in low-dispersion spectra; and (4) strong and rapidly varying polarization at visual and radio wavelengths.
	has synonym BL Lac
	is a kind of blazar
black dwarf	has definition The final stage in the evolution of a star of roughly 1 Msun. It is a mass of cold, electron-degenerate gas, and can no longer radiate energy, because the whole star is in its lowest energy state. No black dwarfs have ever been observed. Also, an object (M < 0.085 Msun) that is not massive enough to achieve nuclear chain reactions.
	is a kind of dwarf
	is a kind of massive compact halo object
black hole	has antonym white hole
	has definition A gravitationally collapsed mass inside the Schwarzschild radius (q.v.), from which no light, matter, or signal of any kind can escape. A black hole occurs when the escape velocity of a body becomes the velocity of light (2GM / R = c2). If an object with the mass of the Sun had a radius of 2.5 km, it would be a black hole. Black holes represent one of the possible endpoints of stellar evolution for stars very much more massive than the Chandrasekhar limit.
	has definition A mass that is sufficiently compact that not even light can escape its intense gravity. Thus it appears black from the outside. If the sun were compressed to a sphere about four miles in diameter, it would become a black hole. It is believed that some massive stars, after exhausting their nuclear fuel, collapse under their own weight to form black holes.
	has definition A singularity in space, surrounded by an event horizon, caused by the collapse of a small but massively dense star through the effects of its own increasing gravity. By the time the state of singularity is reached, the remnants of the star may be minimal, but the gravitational force is so strong it prevents even light from escaping. Black holes may form the "power centers" of galaxies, thus explaining infrared radiation detected in several galactic centres. The properties of matter entering a black hole are the theme of John Wheeler's no hair theorem.
	has definition An object that is maximally gravitationally collapsed, and from which not even light can escape.
	has definition An object with such a strong gravitational field that even light cannot escape. Matter can fall into a black hole, but according to classical physics no matter or energy can leave it. (Hawking has used quantum theory to show that black holes emit blackbody radiation, but the effect is significant only for black holes much smaller than those that are expected to form by the collapse of stars, which have masses of several solar masses or more.)
	is a kind of massive compact halo object
	is a kind of singularity
blazar	has definition A highly variable active galaxy which, in general, displays no emission lines in its spectrum.
	has definition A term collectively used to refer to Optically Violent Variables (OVVs) and BL Lac objects.
	is a kind of active galaxy
	is a kind of radio galaxy
blaze angle	has definition The tilt of the facets or grooves of a diffraction grating.
	is a kind of angle
blazed grating	has definition Diffraction grating so ruled that the reflected light is concentrated into only a few orders, or even a single order, of the spectrum.
	is a kind of diffraction grating
BLS1	has definition Broad Line Seyfert 1
	is a kind of Seyfert galaxy
blue	is a kind of optical
blue compact dwarf galaxy	has acronym BCD
	is a kind of dwarf galaxy
blue compact galaxy	has acronym BCG
	is a kind of galaxy
blue dwarf	has definition High-temperature star (as opposed to red stars). Blue dwarfs represent the very dense, but very small, near-final form of what was once a red giant.
	is a kind of dwarf
blue giant	has definition A giant star with spectral type O or B. [C95]
	has definition High-temperature star (as opposed to red stars). Blue giants are generally on or near the main sequence of the Hertzsprung-Russell diagram.
	is a kind of giant
blue halo star	has definition Hot star in the horizontal-branch, post-horizontal-branch, and post-asymptotic branch phases of evolution.
	is a kind of Population II star
blue haze	has definition A condition in the Martian atmosphere which sometimes makes it opaque to radiation in the blue-violet end of the visible spectrum.
	is a part of Mars
blue horizontal-branch star	has definition Blue horizontal-branch star, the first catalog of which was compiled by Humason and Zwicky.
	has definition Population II star (B3-A0) in the galactic halo, characterized by strong, sharp hydrogen lines and large Balmer jump, and very weak lines of all other elements.
	has synonym HZ star
	is a kind of Population II star
blue supergiant	has definition A supergiant star with spectral type O or B. All blue supergiants are hot and young. Rigel, in the constellation Orion, is the best example.
	is a kind of supergiant
blueshift	has definition The shift of spectral lines toward shorter wavelengths in the spectrum of an approaching source of radiation.
	is a kind of Doppler shift
BM Orionis	has definition A peculiar eclipsing binary (B2-B3) in the Trapezium, with a flat-bottomed light curve suggesting a total eclipse. The spectrum of the secondary has never been seen.
	is a part of Orion
	is an instance of eclipsing binary
Bohr atom	has definition The model of an atom whose electrons are pictured as describing "Keplerian" orbits about the central nucleus.
	is a kind of outdated belief
Bohr magneton	has definition Magnetic moment of an electron in the first Bohr orbit.
	has equation
	has symbol μB
	has uncertainty 0.000037 × 10-26 J T-1
	has value 927.400899 × 10-26 J T-1
	is an instance of electromagnetic constant
Bohr radius	has definition A unit of length based on the radius of the first Bohr orbit of hydrogen 1.
	has equation
	has proposal date 1928
	has proposer Hartree
	has symbol a0
	has symbol a0
	has uncertainty 0.0000000019 × 10-10 m
	has value 0.5291772083 × 10-10 m
	is an instance of atomic constant
	is an instance of length unit
	is an instance of radius
	is named after Niels Bohr
bohrium	is a kind of transactinide
Bok globule	has definition A compact, spherical dark nebula that absorbs radiation. Estimates of their mass suggest that their density is too low for gravitational collapse. They tend to lie in regions of much dust but less gas than would be expected for star-forming regions.
	has radius 103 to 105 AU
	is a kind of dark nebula
	is a part of dust
Bol'shoi Teleskop Azimutal'nyi	has altitude 2100 m
	has aperture 6.00 m
	has comment Primary mirror replaced in about 1984, and a third made of Sitall glass was figured in 1992
	has creation date 1975
	has focal ratio f/4, 30
	has latitude 43° 39' N
	has location Mount Pastukhov, Russia
	has longitude 41° 26'E
	has mirror maker LOMO
	has mirror type Sitall glass
	has mounting manufacturer LOMO
	has owner Special Astrophysical Obs.
	has synonym 6 m
	is an instance of altazimuth telescope
	is an instance of optical telescope
	is an instance of Ritchey-Chrétien
bolometer	has definition A device for measuring the total amount of radiant energy received from a celestial object.
	is a kind of detector
bolometric absolute magnitude	has definition A measure of the total amount of energy radiated by a star at all wavelengths. Mbol of Sun = 4.72 mag. The fraction of total energy emitted by a very blue or very red star that lies in the visible range may differ from the total energy by 4 or 5 mag - i.e., only a few percent of the energy lies in the visible.
	has symbol Mbol
	is a kind of absolute magnitude
Boltzmann constant	has definition The constant of proportionality relating the mean kinetic energy of an atom to its absolute temperature.
	has equation
	has equivalent to molar gas constant divided by the Avogadro number
	has symbol k
	has uncertainty 0.0000024 × 10-23 J K-1
	has value 1.3806503 × 10-23 J K-1
	is an instance of physico chemical constant
boron	has abundance 2.63 × 105 in Sun relative to H = 1 × 1012
	has abundance 4.41 p.p.m. in seawater
	has abundance 950 p.p.m. in Earth's crust
	has atomic emission line 1166.004 nm for B I
	has atomic emission line 1166.247 nm for B I
	has atomic emission line 208.891 nm for B I
	has atomic emission line 208.957 nm for B I
	has atomic emission line 249.667 nm for B I
	has atomic emission line 345.129 nm for B I
	has atomic emission line 249.773 nm for B I (strong)
	has atomic number 5
	has atomic radii 83 pm
	has biological role essential to plants; toxic in excess
	has boiling point 3931 K
	has chief source kernite, borax, ulexite, colemanite
	has covalent radii 88 pm
	has crystal cell dimension a = 506.7, α = 58deg4' pm for α-B
	has crystal type rhombohedral for α-B
	has daily dietary intake 1 - 3 mg
	has definition Non-metal with several forms - the most common form is a dark amorphous powder, unreactive to water, acids and alkalis. Rare and fragile element. Nuclear reactions in stars destroy it. Most boron is created in space, by cosmic rays that smash into heavier atoms and split them.
	has density 2340 kg m-3 for β-rhombohedral solid at 293 K
	has discoverer L.J. Lussac and L.J. Thenard
	has discovery date 1808
	has discovery location Paris, France and London, England
	has electrical resistivity 18000 Ω m at 293 K
	has electron affinity 26.7 kJ mol-1 from B to B-
	has electron configuration [He]2s22p1 in ground state
	has electronegativity 2.04 Pauling
	has hazard boric acid and borates are poisonous, although once used in medicines
	has heat capacity 11.09 J K-1 mol-1 for α solid at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 20.799 J K-1 mol-1 for gas at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 22.2 kJ mol-1
	has heat of vaporization 538.9 kJ mol-1
	has image
	has ionic radii 23 pm for B3+
	has isotope mass range 8 to 13
	has lethal intake 10 - 20 g as boric acid
	has level in humans 0.13 mg dm-3 in blood
	has level in humans 0.33 - 1 p.p.m. in muscle
	has level in humans 0.4 - 3.3 p.p.m. in liver
	has level in humans 1.1 - 3.3 p.p.m. in bone
	has linear expansion coefficient 5 × 10-6 K-1
	has longest lived isotope boron 11
	has main mining area ulexite in USA, Tibet, Chile; colemanite in USA, Turkey
	has mass absorption coefficient 0.392 cm2 g-1 for MoKalpha X-ray diffraction
	has mass absorption coefficient 2.39 cm2 g-1 for CuKalpha X-ray diffraction
	has mass magnetic susceptibility -7.8 × 10-9 kg-1 m3 for solid
	has mass of element in person 18 mg for a 70 kg average person
	has melting point 2573 K
	has mineral borax, colemanite, datolite, kernite, ulexite
	has molar volume 4.62 cm3
	has name origin buraq from Arabic
	has neutron scattering length 0.535 × 10-12 cm
	has number of isotopes 6 including nuclear isomers
	has number of protons 5
	has ocean oxidation state III
	has ocean residence time 1 × 107 years
	has pronunciation bohr-on
	has registry number 7440-42-8 for Chemical Abstracts System database
	has relative atomic mass 10.811 in units of 12C = 12.000
	has reserves 270 × 106 tonnes as B2O3
	has space group R3m for α-B
	has specimen crystals, pieces or powder. Safe.
	has symbol B
has synthesis mechanism
has term symbol 2P1/2 in ground state
has thermal conductivity 27.0 W m-1 K-1 at 300 K
has thermal neutron capture cross section 767 barns
has toxic intake 5 g as boric acid
has uses borosilicate glass, detergents and fire-retardants
has van der Waals radii 208 pm
has world production 1 × 106 tonnes year-1 as B2O3
is a kind of accumulating oceanic element
is a kind of group III element
is a kind of light element
is a kind of nonmetallic metalloid
reacts with metals to form borides
boron 10	has atomic mass 10.0129369
	has magnetogyric ratio 2.8740 × 107 rad T-1 s-1
	has natural abundance 19.9%
	has NMR frequency 10.746 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 22.1 where 13C = 1.00
	has nuclear magnetic moment μ = +1.80065 nuclear magnetons with diamagnetic correction
	has nuclear quadrupole moment 0.08459 × 10-28 m2
	has nuclear spin I = 3+ h/2π
	has number of neutrons 5
	has number of nucleons 10
	has relative NMR sensitivity 0.0199 where 1H = 1.00 using (C2H5)2O/BF3 reference
	has symbol 10B
	has uses Nuclear Magnetic Resonance
	is an instance of boron
boron 11	has atomic mass 11.0093054
	has magnetogyric ratio 8.5794 × 107 rad T-1 s-1
	has natural abundance 80.1%
	has NMR frequency 32.084 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 754 where 13C = 1.00
	has nuclear magnetic moment μ = +2.688637 nuclear magnetons with diamagnetic correction
	has nuclear quadrupole moment 0.04059 × 10-28 m2
	has nuclear spin I = 3/2- h/2π
	has number of neutrons 6
	has number of nucleons 11
	has relative NMR sensitivity 0.17 where 1H = 1.00 using (C2H5)2O/BF3 reference
	has symbol 11B
	has uses Nuclear Magnetic Resonance
	is an instance of boron
boron 12	has atomic mass 12.014352
	has decay mode β- (13.369 Mev)
	has decay mode β-α 1.6%
	has decay mode γ
	has half life 0.0202 seconds
	has nuclear magnetic moment μ = +1.0031 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 1+ h/2π
	has number of neutrons 7
	has number of nucleons 12
	has symbol 12B
	is an instance of boron
boron 13	has atomic mass 13.01778
	has decay mode β- (13.436 Mev)
	has decay mode β-n 0.25%
	has decay mode γ
	has half life 0.0174 seconds
	has nuclear magnetic moment μ = +3.17778 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 3/2+ h/2π
	has number of neutrons 8
	has number of nucleons 13
	has symbol 13B
	is an instance of boron
boron 8	has atomic mass 8.024605
	has decay mode β+ (17.979 Mev)
	has decay mode 2 α
	has half life 0.770 seconds
	has nuclear magnetic moment μ = 1.0355 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 2+ h/2π
	has number of neutrons 3
	has number of nucleons 8
	has symbol 8B
	is an instance of boron
boron 9	has atomic mass 9.013328
	has decay mode p2α
	has half life 8 × 10-19 seconds
	has nuclear magnetic moment μ = +1.8007 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 3/2- h/2π
	has number of neutrons 4
	has number of nucleons 9
	has symbol 9B
	is an instance of boron
Borosilicate	is a kind of mirror
Bose-Einstein nucleus	has definition Nucleus of even A-number (i.e., those with integral spin) (cf. Fermi-Dirac nuclei). Bose-Einstein nuclei do not obey the exclusion principle, and their ground state has zero angular momentum.
	has spin 0
	is a kind of boson
	is a kind of nucleus
boson	has definition A class of elementary particles whose spin is an integer multiple of a fundamental quantized value. The major function of bosons is to mediate the fundamental forces. The best-known boson is the photon.
	has definition A particle which does not obey Pauli's exclusion principle. It is denoted by an integer (or zero) spin.
	has definition A particle, or pattern of string vibration, with a whole number amount of spin; typically a messenger particle.
	has definition A subatomic particle whose spin is an integral multiple of h bar (cf. fermion). Bosons include the photons, the pions, the gravitons, and all Bose-Einstein nuclei. Boson number is not conserved.
	has definition Any particle with integer spin: 0, h bar, 2h bar etc.
	has definition Elementary particles that have integral spins. Force particles such as the photon, gluon, and vector bosons are all bosons. But note that there can also exist composite particles formed out of collections of fermions such as a helium atom-which act collectively as bosons.
	has definition Elementary particles with integer spin that do not obey the Pauli exclusion principle. They include the photons and the W and Z particles, carriers of the electromagnetic and the electroweak forces respectively.
	has quantum behavior Bose-Einstein statistics
	has spin integral
	is a kind of particle
bosonic string theory	has definition First known string theory; contains vibrational patterns that are all bosons.
	is a kind of string theory
bottom	has charge -1/3
	has definition A flavor of quark. See flavor.
	is an instance of heavy quark
bottom-up scenario	has definition A galaxy-formation scenario in which small galaxies form first. Larger and larger structures are then formed in due course.
	has definition The idea that small structures, perhaps galaxies or even smaller substructures, form first in the universe, followed later by larger structures.
	is a kind of galaxy theory
bound electron	has definition Zone in which the electron in atoms reside. Its radius is determined by the quantum principle, its population by the exclusion principle.
	is a kind of electron
bound-bound transition	has definition Transition between energy levels of an electron bound to a nucleus (the electron is bound both before and after the transition).
	is a kind of atomic process
bound-free transition	has definition Transition in which a bound electron in any energy level is liberated or its reverse process.
	is a kind of atomic process
Bowen fluorescence mechanism	has definition A mechanism first discovered by Bowen which explains the anomalously strong lines of O III in the spectra of some planetary nebulae as fluorescence involving the radiative excitation of the 2p3d 3Po2 level of O2+ (54.71 eV) from the 2p2 3P2 state in the ground term by He II Lyman-α photons (54.17 eV).
	is a kind of fluorescence
Boyle's law	has definition The pressure of an ideal gas kept at constant temperature varies inversely as the volume, i.e., directly as the density.
	is an instance of gas law
Boötes	has acronym Boo
	has boundary
	has genitive Boötis
	has historical image
	has historical origin the bear hunter which circles the bears, Ursa Major and Ursa Minor, around the North Pole
	has synonym Bear Driver
	has synonym Bear Hunter
	has synonym Herdsman
	is a part of celestial sphere
	is an instance of constellation
Bp star	has definition Peculiar B stars whose spectra show a deficiency in helium and in which the lines of one or several elements are abnormally enhanced. Traditionally the most important subgroups are Si λ4200, Hg-Mn and Cr-Eu-Sr stars. The latest objects of the latter group correspond to early F-type.
	is a kind of B star
	is a kind of peculiar star
Br alpha	has wavelength 40512 Å
	is an instance of Brackett line
Brackett line	has lower energy level 4
	is a kind of hydrogen line
	is a kind of spectral series line
Bragg angle	has definition Glancing angle between an incident X-ray beam and a given set of crystal planes for which the secondary X-radiation from the planes combines to give a single reflected beam.
	is a kind of angle
brane	has definition Any of the extended objects that arise in string theory. A one-brane is a string, a two-brane is a membrane, a three-brane has three extended dimensions, etc. More generally, a p-brane has p spatial dimensions.
	is a kind of string theory
bremsstrahlung	has antonym inverse bremsstrahlung
	has definition Electromagnetic radiation given out by electrons interacting with the ions in an ionized gas.
	has definition Radiation emitted or absorbed when a free electron is accelerated in the field of an atomic nucleus but remains in a hyperbolic orbit without being captured. Since bremsstrahlung is not quantized, photons of any wavelength can be emitted or absorbed. (Also called a free-free transition because the electron is free both before and after the transition.)
	has synonym deceleration radiation
	has synonym free-free transition
	is a kind of emission
	is a kind of free-free transition
bright blue variable	has definition Early-type high-luminosity star with peculiar spectra and large-amplitude light variations over a long time scale.
	is a kind of variable
bright giant	has luminosity class II
	is a kind of star
bright point	has definition Bright region (in X-ray and XUV) observed on the Sun during Skylab missions.
	has diameter 20000 km
	has discoverer Skylab
	has distribution uniform
	has electron temperature 1 to 2 × 106 K
	has mean lifetime 8 hours
	is a part of photosphere
bright ring	is a kind of ring
	is a part of Saturn ring system
Brillouin scattering	has definition Slight changes in the frequency of radiation, caused by reflection or scattering from the high-frequency sound waves that arise from thermal vibrations of atoms in the medium.
	is a kind of scattering
Broad-line radio galaxy	has acronym BLRG
	is a kind of radio galaxy
bromine	has image
	has ocean oxidation state -I
	has ocean residence time 1 × 108 years
	is a kind of accumulating oceanic element
	is a kind of atmophile element
	is a kind of halogen
	is a kind of liquid element
brown dwarf	has definition A self-gravitating, self-luminous gaseous object which is not sufficiently massive to result in thermonuclear hydrogen fusion reactions in its core and cannot therefore be considered a star. Such objects are expected to have a mass less than 7% of the Sun's mass and represent a "missing link" between low-mass stars and gas giant planets like Jupiter (at 0.1% of the Sun's mass).
	has definition A substellar object that is below the minimum mass required for nuclear fusion reactions to occur in its core.
	has definition Star with too little mass to ignite its hydrogen 1 fuel. If brown dwarfs exist, they shine faint red for a time, as they convert gravitational energy into heat, and then fade and cool.
	has mass 1 to 8 percent of the Sun
	is a kind of dwarf
	is a kind of massive compact halo object
Bruce medalist	has definition a scientist who was awarded the Bruce Medal
	is a kind of scientist
bulge	has definition The stellar population that lies within several thousand light-years of the Galactic center. The bulge is old, dense, and metal-rich.
	is a part of galactic nucleus
Bureau des Longitudes	has acronym BDL
	is an instance of science institution
Bureau International de l'Heure	has acronym BIH
	is an instance of science institution
Bureau International des Poids et Mesures	has acronym BIPM
	is an instance of science institution
Bw star	has definition B star with weak helium lines - i.e., B stars which, if classified according to their colors, would have helium lines too weak for the classification, and which, if classified according to their helium lines, would have colors too blue for their spectral type.
	is a kind of B star
Byurakan 2.6-meter Reflector	has altitude 1500 m
	has aperture 2.64 m
	has creation date 1976
	has focal ratio f/3.6, 16, 40
	has latitude 40° 20' N
	has location Mount Aragatz, Armenia
	has longitude 44° 18' E
	has mounting manufacturer LOMO
	has owner Byurakan Observatory
	has synonym Byurakan 102 inch
	is an instance of Fork equatorial telescope
	is an instance of optical telescope
	is an instance of reflector
C star	has definition A class of carbon star, defined by Morgan and Keenan to replace the Harvard R and N spectral classes.
	has definition Late type giant with strong bands of carbonated molecules (C2, CN, CH) and no metallic oxide bands. Formerly they were called R or N types, the R types being the hotter and the N types the cooler C stars.
	is a kind of carbon star
C. Donald Shane Telescope	has altitude 1290 m
	has aperture 3.05 m
	has creation date 1959
	has focal ratio f/5, 17, 36
	has latitude 37° 21' N
	has location Mount Hamilton, Calif., US
	has longitude 121° 38' W
	has mirror maker Don O. Hendrix
	has mirror type Pyrex
	has mounting manufacturer Judson Pacific-Murphy Corp.
	has owner Lick Observatory
	has synonym 120 inch
	is an instance of Cassegrain
	is an instance of Fork equatorial telescope
	is an instance of optical telescope
C2 band	has species C2 radical
	is a kind of molecular band
Ca H line	has definition A spectral line of singly ionized calcium.
	has wavelength 3968 Å
	is a kind of HK lines
Ca K line	has definition A spectral line of singly ionized calcium.
	has wavelength 3933 Å
	is a kind of HK lines
cadmium	has image
	has ocean oxidation state II
	has ocean residence time 30 years
	is a kind of chalcophile element
	is a kind of recycled oceanic element
	is a kind of transition metal
Caelum	has acronym Cae
	has genitive Caeli
	has synonym Chisel
	is a part of celestial sphere
	is an instance of constellation named by de Lacaille
Calar-Alto-Schmidtspiegel	has altitude 2168 m
	has aperture 0.80 m
	has comment Tube and optics moved from Hamburg, Germany, where the instrument had been in use since 1955
	has creation date 1980
	has focal ratio f/3.0
	has latitude 37° 13' N
	has location Calar Alto, Spain
	has longitude 2° 32' W
	has mirror diameter 1.2 m
	has mirror maker Zeiss (Jena)
	has mounting manufacturer Grubb-Parsons
	has owner Calar Alto Observatory
	has synonym Calar Alto Schmidt
	is an instance of Fork equatorial telescope
	is an instance of Schmidt
calcium	has abundance 2.24 × 106 in Sun relative to H = 1 × 1012
	has abundance 390 p.p.m. in Atlantic surface seawater
	has abundance 390 p.p.m. in Pacific surface seawater
	has abundance 41000 p.p.m. in Earth's crust
	has abundance 430 p.p.m. in deep Atlantic seawater
	has abundance 440 p.p.m. in deep Pacific seawater
	has atomic emission line 239.856 nm for Ca I
	has atomic emission line 317.933 nm for Ca II
	has atomic emission line 373.690 nm for Ca II
	has atomic emission line 393.366 nm for Ca II (strong)
	has atomic emission line 393.847 nm for Ca II
	has atomic emission line 422.673 nm for Ca I (used in atom absorption spectrometry)
	has atomic number 20
	has atomic radii 197 pm for α-form
	has biological role essential to all species
	has boiling point 1757 K
	has bulk modulus 17.2 GPa
	has chief source calcite, dolomite, gypsum (used in cement and plaster) anhydrite (used to make H2SO4)
	has covalent radii 174 pm
	has crystal cell dimension a = pm
	has crystal type
	has daily dietary intake 600 - 1400 mg
	has definition silvery-white, relatively soft metal
	has density 1365 kg m-3 for liquid at 1112 K melting point
	has density 1550 kg m-3 for solid at 293 K
	has discoverer Sir Humphry Davy
	has discovery date 1808 (isolated)
	has discovery location London, England
	has electrical resistivity 3.43 × 10-8 Ω m at 293 K
	has electron affinity -186 kJ mol-1 from Ca to Ca-
	has electron configuration [Ar]4s2 in ground state
	has electronegativity 1.00 Pauling
	has hazard calcium compounds are only toxic via the other elements they contain
	has heat capacity 20.786 J K-1 mol-1 for gas at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 25.31 J K-1 mol-1 for solid α form at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 9.33 kJ mol-1
	has heat of vaporization 149.95 kJ mol-1
	has image
	has ionic radii 106 pm for Ca2+
	has isotope mass range 36 to 51
	has lethal intake 6.45 grams kg-1 in carbonate form for rat
	has level in humans 100 - 360 p.p.m. in liver
	has level in humans 140 - 700 p.p.m. in muscle
	has level in humans 170000 p.p.m. in bone
	has level in humans 60.5 mg dm-3 in blood
	has linear expansion coefficient 22 × 10-6 K-1
	has longest lived isotope
	has main mining area common everywhere
	has mass absorption coefficient 162 cm2 g-1 for CuKα X-ray diffraction
	has mass absorption coefficient 18.3 cm2 g-1 for MoKα X-ray diffraction
	has mass magnetic susceptibility +1.4 × 10-8 kg-1 m3 for solid
	has mass of element in person 1.00 kg for a 70 kg average person
	has melting point 1112 K
	has mineral anhydrite, aragonite, calcite, dolomite, gypsum, shortite, vaterite
	has molar volume 25.86 cm3
	has name origin calx = lime from Latin
	has neutron scattering length 0.476 × 10-12 cm
	has number of isotopes 16 including nuclear isomers
	has number of protons 20
	has ocean oxidation state II
	has ocean residence time 1 × 106 years
	has poisson's ratio 0.31 GPa
	has pronunciation kal-sium
	has registry number 7440-70-2 for Chemical Abstracts System database
has relative atomic mass 40.078 in units of 12C = 12.000
has reserves almost unlimited
has rigidity modulus 7.9 GPa
has space group
has specimen granules, pieces or turings. Care !
has symbol Ca
has synthesis mechanism heat calcium oxide (CaO) with aluminium metal in vacuum
has term symbol 1S0 in ground state
has thermal conductivity 200 W m-1 K-1 at 300 K
has thermal neutron capture cross section 0.43 barns
has toxic intake non-toxic
has uses alloys and in the manufacture of zirconium, thorium, and uranium and the rare earth metals
has uses CaO used in metallurgy, water treatment, chemicals industry, cement, etc
has world production 112 × 106tonnes year-1 for lime, CaO
has world production 2000 tonnes year-1 for calcium metal
has young's modulus 19.6 GPa
is a kind of alkali earth metal
is a kind of lithophile element
is a kind of recycled oceanic element
reacts with oxygen and water but soon forms a thin protective oxide-nitride film preventing further corrosion
calcium 40	has atomic mass 39.9625906
	has natural ab39undance 96.941%
	has nuclear magnetic moment μ = 0 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 0+ h/2π
	has number of neutrons 20
	has number of nucleons 40
	has symbol 40Ca
	has uses isotopically enriched samples available for experimental purposes
	is an instance of calcium
calcium 41	has atomic mass 40.962278
	has decay mode EC (0.421 Mev)
	has decay mode no γ
	has half life 1.03 × 105 years
	has nuclear magnetic moment μ = -1.595 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 7/2- h/2π
	has number of neutrons 21
	has number of nucleons 41
	has symbol 41Ca
	has uses research
	is an instance of calcium
calcium 42	has atomic mass 41.9586176
	has natural abundance 0.647%
	has nuclear magnetic moment μ = 0 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 0+ h/2π
	has number of neutrons 22
	has number of nucleons 42
	has symbol 42Ca
	has uses isotopically enriched samples available for experimental purposes
	is an instance of calcium
calcium 43	has atomic mass 42.9587662
	has magnetogyric ratio -1.8001 × 107 rad T-1 s-1
	has natural abundance 0.135%
	has NMR frequency 6.728 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 0.0527 where 13C = 1.00
	has nuclear magnetic moment μ = -1.31727 nuclear magnetons with diamagnetic correction
	has nuclear quadrupole moment -0.0408 × 10-28 m2
	has nuclear spin I = 7/2- h/2π
	has number of neutrons 23
	has number of nucleons 43
	has relative NMR sensitivity 6.40 × 10-3 where 1H = 1.00
	has symbol 43Ca
	has uses Nuclear Magnetic Resonance, E
	is an instance of calcium
calcium 44	has atomic mass 43.9554806
	has natural abundance 2.086%
	has nuclear magnetic moment μ = 0 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 0+ h/2π
	has number of neutrons 24
	has number of nucleons 44
	has symbol 44Ca
	has uses isotopically enriched samples available for experimental purposes
	is an instance of calcium
calcium 45	has atomic mass 44.956185
	has decay mode β- (0.257 Mev)
	has decay mode no γ
	has half life 162.7 days
	has nuclear magnetic moment μ = -1.327 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 7/2- h/2π
	has number of neutrons 25
	has number of nucleons 45
	has symbol 45Ca
	has uses research
	is an instance of calcium
calcium 46	has atomic mass 45.953689
	has natural abundance 0.004%
	has nuclear magnetic moment μ = 0 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 0+ h/2π
	has number of neutrons 26
	has number of nucleons 46
	has symbol 46Ca
	has uses isotopically enriched samples available for experimental purposes
	is an instance of calcium
calcium 47	has atomic mass 46.954543
	has decay mode β- (1.988 Mev)
	has decay mode γ
	has half life 4.536 days
	has nuclear magnetic moment μ = -1.38 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 7/2- h/2π
	has number of neutrons 27
	has number of nucleons 47
	has symbol 47Ca
	has uses research, medical diagnosis
	is an instance of calcium
calcium 48	has atomic mass 47.952533
	has natural abundance 0.187%
	has nuclear magnetic moment μ = 0 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 0+ h/2π
	has number of neutrons 28
	has number of nucleons 48
	has symbol 48Ca
	has uses isotopically enriched samples available for experimental purposes
	is an instance of calcium
calcium 49	has atomic mass 48.955672
	has decay mode β- (5.263 Mev)
	has decay mode γ
	has half life 8.72 minutes
	has nuclear spin I = 3/2- h/2π
	has number of neutrons 29
	has number of nucleons 49
	has symbol 49Ca
	is an instance of calcium
calendar year	has definition is an approximation to the tropical year.
	is an instance of year
	see also Gregorian calendar
California Institute of Technology	has acronym Caltech
	has location Pasadena, USA
	is an instance of science institution
californium	has image
	is a kind of transuranium element
Callisto	has albedo 0.15
	has definition A Galilean satellite of Jupiter. It has the lowest density, lowest albedo, and highest temperature of any of the four main satellites of Jupiter.
	has definition Fifth (known) moon out from jupiter, and its second largest.
	has density 1.7 g cm-3
	has diameter 5050 km
	has orbital parameters e = 0.0075; i = 0°.3
	has orbital rotation period 16.7 days
	has synonym J IV
	has synonym Jupiter IV
	has temperature 156 K
	is a part of Jupiter
	is an instance of Galilean satellite
CalTech Submillimeter Observatory	has acronym CSO
	is an instance of observatory
cambrian period	has duration 100 million years
	has start time 600 million years ago
	is a kind of paleozoic era
Cambridge catalog	has definition The results of five intensive radio-astronomical surveys (1C, 2C, 3C, 4C and 5C) under the direction of Sir Martin Ryle and Anthony Hewish, during the l950s, 1960s and 1970s, at Cambridge.
	is a kind of radio source catalog
Camelopardalis	has acronym Cam
	has genitive Camelopardalis
	has historical image
	has synonym Giraffe
	is a part of celestial sphere
	is an instance of constellation
Canada-France-Hawaii Telescope	has acronym CFHT
	has altitude 4200 m
	has aperture 3.58 m
	has creation date 1979
	has focal ratio f/3.8, 8, 20, 35
	has latitude 19° 49' N
	has location Mauna Kea, Hawaii, US
	has longitude 155° 28' W
	has mirror maker Dominion Astrophys. Obs.
	has mirror type Cer-Vit
	has mounting manufacturer SNACRP
	has owner Canada-France-Hawaii Telescope Corp.
	is an instance of Horseshoe equatorial telescope
	is an instance of optical telescope
	is an instance of reflector
Cancer	has acronym Cnc
	has boundary
	has genitive Cancri
	has historical image
	has historical origin the crab sent by Hera to distract Hercules from his battle with the Hydra
	has synonym Crab
	is a part of Zodiac
	is an instance of zodiacal constellation
candela	has approval agency 13th CGPM
	has approval date 1967
	has definition the luminous intensity in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian
	has definition The SI unit of luminous intensity, defined as "the luminous intensity, in the perpendicular direction, of a surface of 1/600000 square meter of a blackbody at the temperature of freezing platinum under a pressure of 101325 newtons per square meter."
	has historical origin in 1933 it was based on the luminous emission of a blackbody at the freezing temperature of platinum (2045 K)
	has symbol cd
	is an instance of base SI unit
	is an instance of luminous intensity unit
Canes Venatici	has acronym CVn
	has boundary
	has genitive Canum Venaticorum
	has historical image
	has historical origin the hunting dogs held on a leash by Boötes as he hunts for the bears Ursa Major and Ursa Minor
	has synonym Hunting Dogs
	is a part of celestial sphere
	is an instance of constellation
	named by Johannes Hevelius in 1687
Canis Major	has acronym CMa
	has boundary
	has genitive Canis Majoris
	has historical origin one of Orion's hunting dogs
	has synonym Big Dog
	is a part of celestial sphere
	is an instance of constellation
Canis Minor	has acronym CMi
	has genitive Canis Minoris
	has historical origin one of Orion's hunting dogs
	has synonym Little Dog
	is a part of celestial sphere
	is an instance of constellation
Canopus	has B-V magnitude 0.15
	has declination -52 41 44
	has definition A supergiant, the second brightest star in the southern sky.
	has distance 55 pc
	has right ascension 06 23 57.2
	has spectral type F0 Ib
	has spectral type F0II
	has synonym alpha Car
	has synonym HR 2326
	has V magnitude -0.72
	is a part of Carina
	is an instance of F star
	is an instance of naked eye star
	is an instance of supergiant
Canum Venaticorum	has B-V magnitude -0.12
	has declination +38 19 6
	has right ascension 12 56 1.6
	has spectral type A0pSiEuHg
	has synonym HR 4915
	has V magnitude 2.90
	is a part of Canes Venatici
	is an instance of A star
	is an instance of naked eye star
capacitance	has unit capacitance unit
	is a kind of electromagnetic quantity
capacitance unit	is a kind of electromagnetic unit
	is a unit of capacitance
Capella	has B-V magnitude 0.80
	has declination +45 59 53
	has definition The sixth brightest star in the night sky, consists of two yellow giants. A spectroscopic triple (F8-G0 III, G5 III, M5 V) (1974 parallax 0'.079). It has a high lithium content and a nearly circular orbit. It may be an X-ray source.
	has distance 13 pc
	has orbital period 104.023 days
	has right ascension 05 16 41.3
	has spectral type G5IIIe+G0III
	has synonym Alpha Aurigae
	has synonym HR 1708
	has V magnitude 0.08
	is a part of Auriga
	is an instance of G star
	is an instance of giant
	is an instance of naked eye star
Capricornus	has acronym Cap
	has boundary
	has genitive Capricorni
	has historical image
	has historical origin a goat with a fish tail
	has synonym Goat
	is a part of Zodiac
	is an instance of zodiacal constellation
carbon	has abundance 23 p.p.m. in Atlantic surface seawater
	has abundance 26 p.p.m. in deep Atlantic seawater
	has abundance 26 p.p.m. in Pacific surface seawater
	has abundance 28 p.p.m. in deep Pacific seawater
	has abundance 350 p.p.m. by volume in Earth's atmosphere as CO2
	has abundance 4.17 × 108 in Sun relative to H = 1 × 1012
	has abundance 480 p.p.m. in Earth's crust
	has atomic emission line 247.856 nm for C I
	has atomic emission line 283.671 nm for C II (strong)
	has atomic emission line 426.726 nm for C II (strong)
	has atomic emission line 723.642 nm for C II (strong)
	has atomic number 6
	has atomic radii 77 pm
	has biological role DNA constituent, organic molecules required for life
	has boiling point 5100 K (sublimes)
	has chief source graphite
	has covalent radii 60 pm for triple bonds
	has covalent radii 67 pm for double bonds
	has covalent radii 77 pm for single bond
	has crystal cell dimension a = 1414 pm for buckminsterfullerene
	has crystal cell dimension a = 246, c = 670.78 pm for hexagonal graphite
	has crystal cell dimension a = 252, c = 412 pm for hexagonal diamond
	has crystal cell dimension a = 356.703 pm for cubic diamond
	has crystal cell dimension a = 364.2 pm, α = 39°30' for rhombohedral graphite
	has crystal cell dimension a = 894.8, c = 1408 pm for hexagonal carbon (chaoite)
	has crystal type cubic for cubic diamond
	has crystal type f.c.c. for buckminsterfullerene
	has crystal type hexagonal for hexagonal carbon (chaoite)
	has crystal type hexagonal for hexagonal diamond
	has crystal type hexagonal for hexagonal graphite
	has crystal type rhombohedral for rhombohedral graphite
	has daily dietary intake 300 g
	has definition pure forms occur as graphite, diamond and buckminsterfullerene C60
	has density 1650 kg m-3 for buckminsterfullerene at 293 K
	has density 2260 kg m-3 for graphite at 293 K
	has density 3513 kg m-3 for diamond at 293 K
	has discovery date pre-historic
	has electrical resistivity 1 × 1011 Ω m for diamond at 293 K
	has electrical resistivity 1 × 1014 Ω m for buckminsterfullerene at 293 K
	has electrical resistivity 1.375 × 10-5 Ω m for graphite at 293 K
	has electron affinity 121.9 kJ mol-1 from C to C-
	has electron configuration [He]2s22p2 in ground state
	has electronegativity 2.55 Pauling
	has hazard carbon black is a nuissance but not dangerous, although soot may harbour carcinogenic materials
	has heat capacity 20.838 J K-1 mol-1 for gas at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 6.113 J K-1 mol-1 for solid diamond at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 8.527 J K-1 mol-1 for solid graphite at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 105.1 kJ mol-1
	has heat of vaporization 710.9 kJ mol-1
	has image
	has ionic radii 260 pm for C4-
	has isotope mass range 9 to 16
	has level in humans 0.0016 - 0.075 mg dm-3 in blood
	has level in humans 300000 p.p.m. in bone
	has level in humans 670000 p.p.m. in liver
	has level in humans 670000 p.p.m. in muscle
	has linear expansion coefficient 1.19 × 10-6 K-1 for diamond
	has longest lived isotope carbon 12
	has main mining area diamond deposits in South Africa, USA, Russia, Brazil, Zaire, Sierra Leone, Ghana, Canada
	has main mining area graphite deposits in Sri Lanka, Madagascar, Russia, South Korea, Mexico, Czech Republic, Italy
	has mass absorption coefficient 0.625 cm2 g-1 for MoKα X-ray diffraction
	has mass absorption coefficient 4.60 cm2 g-1 for CuKα X-ray diffraction
	has mass magnetic susceptibility -6.2 × 10-9 kg-1 m3 for diamond
	has mass magnetic susceptibility -6.3 × 10-9 kg-1 m3 for graphite
has mass of element in person 16 kg for a 70 kg average person
has melting point 3800 K for graphite
has melting point 3820 K for diamond
has melting point 800 K for buckminsterfullerene (sublimes)
has mineral diamond, graphite, calcium magnesium carbonates, fossil fuel
has molar volume 3.42 cm3 for diamond
has name origin carbo = charcoal from Latin
has neutron scattering length 0.66460 × 10-12 cm
has number of isotopes 8 including nuclear isomers
has number of protons 6
has ocean oxidation state IV
has ocean residence time 800000 years
has pronunciation kar-bon
has registry number 7440-44-0 for Chemical Abstracts System database
has relative atomic mass 12.011 in units of 12C = 12.000
has reserves 1000 × 109 tonnes for coal
has reserves 127 × 109 tonnes for natural gas
has reserves 140 × 109 tonnes for oil
has reserves large for tar sands
has space group Fd3m for cubic diamond
has space group P63/mmc for hexagonal diamond
has space group P63mc for hexagonal graphite
has space group R3m for rhombohedral graphite
has specimen amorphous, fullerenes, bucky tubes, diamond, graphite and soot. Safe.
has symbol C
has synthesis mechanism
has term symbol 3P0 in ground state
has thermal conductivity 1960 W m-1 K-1 for graphite at 298 K along sheets
has thermal conductivity 5.7 W m-1 K-1 for graphite at 298 K perpendicular to sheets
has thermal conductivity 990 - 2320 W m-1 K-1 for diamond at 298 K
has thermal neutron capture cross section 0.0035 barns
has toxic intake non-toxic, but some compounds can be very toxic such as CO or CN-
has uses coke in steel, carbon black in printing, as a filler, activated charcoal for water treatement and respirators
has van der Waals radii 185 pm
has world production 8.6 ×
is a kind of atmophile element
is a kind of group IV element
is a kind of nonmetallic element
is a kind of recycled oceanic element
is a kind of siderophile element
reacts with almost everything
carbon 10	has atomic mass 10.01686
	has decay mode β+ (3.650 Mev)
	has decay mode γ
	has half life 19.3 seconds
	has nuclear spin I = 0+
	has number of neutrons 4
	has number of nucleons 10
	has symbol 10C
	is an instance of carbon
carbon 11	has atomic mass 11.01143
	has decay mode β+ EC (1.982 Mev)
	has decay mode γ
	has half life 20.3 minutes
	has nuclear magnetic moment μ = -0.964
	has nuclear spin I = 3/2-
	has number of neutrons 5
	has number of nucleons 11
	has symbol 11C
	has uses
	is an instance of carbon
carbon 12	has atomic mass 12.000000000 by definition
	has natural abundance 98.90 %
	has nuclear magnetic moment μ = 0
	has nuclear spin I = 0+
	has number of neutrons 6
	has number of nucleons 12
	has symbol 12C
	is an instance of carbon
carbon 13	has atomic mass 13.003354826
	has magnetogyric ratio × 10 rad T-1 s-1
	has natural abundance 1.10 %
	has NMR frequency MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity where 13C = 1.00
	has nuclear magnetic moment μ = +0.702411
	has nuclear quadrupole moment × 10- m2
	has nuclear spin I = 1/2-
	has number of neutrons 7
	has number of nucleons 13
	has relative NMR sensitivity where 1H = 1.00
	has symbol 13C
	has uses Nuclear Magnetic Resonance
	is an instance of carbon
carbon 14	has atomic mass 14.003241
	has decay mode β- (0.15648 Mev)
	has decay mode no γ
	has half life 5715 years
	has natural abundance traces
	has nuclear spin I = 0+
	has number of neutrons 8
	has number of nucleons 14
	has symbol 14C
	has uses research, carbon dating
	is an instance of carbon
carbon burning	has definition The stage when a star fuses carbon into heavier elements, making neon and magnesium. Carbon burning eventually occurs in all stars born with more than eight solar masses.
	has duration 600 years
	has location center of star heavier than 4 solar masses
	has optimum density 2 × 105 g cm-13
	has optimum temperature 6 × 108 K
	has part product neon, magnesium
	has reactant carbon
	is a kind of exothermic fusion process
	requires minimum mass at star birth 8 solar masses
carbon cycle	has catalyst carbon, nitrogen and oxygen
	has definition A series of nuclear reactions in which carbon is used as a catalyst to transform hydrogen into helium. The carbon cycle can take place only if the necessary C and N nuclei are present, and it requires higher temperatures and is far more temperature-dependent than the proton-proton chain. The cycle yields 26.7 MeV of energy. (On the average, 1.7 MeV of this energy is carried away because of neutrino losses.)
	has definition An important nuclear fusion process that occurs in stars. Carbon 12 both initiates it and, following interactions with nuclei of nitrogen, hydrogen, oxygen, and other elements, reappears at its conclusion.
	has definition One way that a star converts hydrogen into helium. During the CNO cycle, carbon, nitrogen, and oxygen catalyze the nuclear reaction, so the total number of carbon, nitrogen, and oxygen nuclei remains the same. However, carbon and oxygen gradually get converted into nitrogen. The CNO cycle powers the hydrogen burning that occurs in main-sequence stars with more than 1.5 solar masses and in giants and supergiants of all masses.
	has definition Use of carbon and nitrogen as intermediates in the nuclear fusion process of the Sun. Cooler stars undergo the proton-proton cycle.
	has discovered date 1938
	has minimum mass 1.5 solar masses
	has minimum temperature 15 to 20 million Kelvin
	has part catalyst carbon
	has part catalyst nitrogen
	has part catalyst oxygen
	has part product helium
	has part reactant proton
	has reaction 12C(p, γ) 13N(p, γ) 14O(β+ν) 14N(p, γ) 15O(β+ν) 15N(p, α) 12C
	has synonym Bethe-Weizsäcker cycle
	has synonym CNO cycle
	has temperature dependence E ∝ T15
	is a kind of hydrogen burning
	produces energy 26.7 MeV
carbon detonation supernova model	has definition A supernova model involving the explosive ignition of carbon in the high-density (108 - 1010 g cm-3), electron-degenerate carbon-oxygen core of a 6±2 - 7±2 Msun star by the formation and propagation of a detonation wave. A carbon-detonation supernova seems to leave no dense remnant and converts its C-O core entirely to iron.
	is a kind of stellar theory
carbon monosulfide	has symbol CS
	is an instance of diatomic molecule
	is an instance of interstellar molecule
carbon monoxide	has definition A molecule consisting of one carbon atom and one oxygen atom. It is the most abundant interstellar molecule after molecular hydrogen and is especially useful because it radiates at radio wavelengths, so astronomers can use it to map the distribution of molecular hydrogen.
	has symbol CO
	is an instance of diatomic molecule
	is an instance of interstellar molecule
	is an instance of neutral particle
carbon star	has definition In the HD system, a rather loose category of peculiar red-giant star, usually of spectral types R and N, whose spectra show strong bands of C2, CN, or other carbon compounds and unusually high abundances of lithium. Carbon stars resemble S stars in the relative proportion of heavy and light metals, but they contain so much carbon that these bands dominate their spectra. (C2,0. The number following the comma is an abundance parameter.)
	is a kind of late star
carbonyl sulfide	has symbol OCS
	is an instance of interstellar molecule
Carina	has acronym Car
	has boundary
	has genitive Carinae
	has synonym Keel
	is a part of celestial sphere
	is an instance of constellation formerly part of Argo Navis
	was named by the IAU along with Vela, Puppis and Pyxis
Carina galaxy	has definition A dwarf galaxy that orbits the Milky Way.
	has discovery date 1977
	has distance from galaxy center 350000 light-years
	is a part of Carina
	is a part of Local Group
	is an instance of satellite galaxy
	orbits Milky Way
Carina Nebula	has image
	has synonym NGC 3372
	is an instance of gaseous nebula
Carina OB 2	has definition A rich association of OB stars near η Carinae.
	is a part of Carina
	is an instance of OB association
carrier boson	carries the force
	has definition A particle that carries one of the fundamental forces between other interacting particles. For example, the carrier boson for the electromagnetic force is the photon.
	has definition Particle that acts as the transmitters of forces. The best known example is the photon, which transmits electromagnetic forces. The gluons are the transmitters of the strong interactions, and the W+, W-, and Z0 particles are the transmitters of the weak interactions. See Table 7.1 on page 120.
	has synonym force carrier
	is a kind of boson
	is a kind of elementary particle
Cassegrain	has definition An optical arrangement in which light rays striking the parabolic concave primary mirror of a reflecting telescope are reflected to the hyperbolic convex secondary mirror, and re-reflected through a hole bored in the primary to a focus behind it.
	has definition Refers to a design of reflecting telescopes in which the light collected and focussed by the large concave primary mirror is refocussed by a smaller convex secondary mirror on the same axis as the primary. The refocussed beam passes through a central hole cut into the primary mirror and emerges behind the primary.
	has definition Telescope devised by Cassegrain in which an auxiliary convex mirror reflects the magnified image, upside down, through a hole in the center of the main objective mirror - i.e., through the end of the telescope itself. It was, however, no improvement on the gregorian telescope invented probably slightly earlier.
	has optical design Cassegrain
	has primary mirror shape concave paraboloid
	has secondary mirror shape convex hyperboloid
	is a kind of reflector
Cassini's division	has definition A gap between the outermost rings of Saturn. The period of a particle in Cassini's division is about two-thirds that of Janus, one-half that of Mimas, one-third that of Enceladus, and one-quarter that of Tethys.
	has discoverer Cassini
	has discovery date 1675
	has width 1800 km
	is a kind of ring gap
	is a part of Saturn ring system
Cassiopeia	has acronym Cas
	has boundary
	has genitive Cassiopeiae
	has historical image
	has historical origin Cassiopeia is chained to her throne as punishment for her boastfulness
	has synonym Andromeda's Mother
	has synonym Queen of Ethiopia
	is a part of celestial sphere
	is an instance of constellation
Cassiopeia A	has definition A radio source in Cassiopeia, the strongest extrasolar source in the sky, believed to be the remnant of a Type II supernova whose light reached Earth about 1667. Optically it is a faint nebula. It has a mass of a few solar masses. It is also an extended source of soft X-rays.
	has distance 3 kpc
	has expansion velocity 800 km s-1
	has synonym 3C 461
	has synonym 3U 2321+58
	is a part of Cassiopeia
	is an instance of radio source
	is an instance of X-ray source
Cat's Eye	has distance 3000 light years
	has image
	has synonym NGC 6543
	is an instance of planetary nebula
	is part of Draco
cataclysmic variable	has acronym CV
	has definition A collective name for stars in which the brightness increases suddenly because of an explosive event. The class comprises supernovae, novae, recurrent novae, dwarf novae and flare stars.
	has definition A type of variable including flare stars and novae (common, recurrent, and dwarf), all of which are believed to be very close binary systems in which hydrogen-rich matter flows from a late-type star onto a hot white-dwarf primary.
	has outburst start time
	has peak brightness
	has recovery time
	has synonym eruptive variable
	has synonym explosive variable
	is a kind of irregular variable
catalog about star systems	has object type collection of stars
	is a kind of astronomical catalog
catastrophism	has antonym uniformitarianism
	has definition Nineteenth-century hypothesis that depicted the many changes evinced by the geological record as having resulted from cataclysms occurring during a relatively brief period of history.
	is a kind of doctrine
causality	has definition The doctrine that every new situation must have resulted from a previous state. Causation underlay the original atomic hypothesis of the Greeks, and was popular in classical physics. It is eroded in quantum mechanics and has, in any case, never been proved essential to the scientific world view. See chance, determinism.
	has synonym causation
	is a kind of doctrine
CDA	has definition Centre de Donnees Astronomiques (Strasbourg, France).
	is an instance of database
Cecilia Payne Gaposhkin	has career Havard College Observatory
	is an instance of 19th century scientist
	is an instance of astronomer
celestial body	has definition natural object visible in the sky
	has spectra
	is a kind of natural object
celestial ephemeris pole	has definition The reference pole for nutation and polar motion; the axis of figure for the mean surface of a model Earth in which the free motion has zero amplitude. This pole has no nearly diurnal nutation with respect to a space-fixed or Earth-fixed coordinate system.
	is an instance of equatorial coordinate
celestial equator	has definition Projection of the Earth's equator as a line across the sky (so that to an observer actually on the equator, such a line would pass through the zenith). The directional bearing of a star is given in terms of its right ascension round the celestial equator.
	is a kind of equator
celestial event	has definition Event involving one or more celestial objects
	is a kind of event
celestial latitude	has definition Angular distance on the celestial sphere measured north or south of the ecliptic along the great circle passing through the poles of the ecliptic and the celestial object.
	is an instance of angle
	is an instance of ecliptic coordinate component
celestial longitude	has definition Angular distance along the ecliptic from the vernal equinox eastward.
	has definition Angular distance on the celestial sphere measured eastward along the ecliptic from the dynamical equinox to the great circle passing through the poles of the ecliptic and the celestial object.
	is an instance of angle
	is an instance of ecliptic coordinate component
celestial mechanics	has definition Study of the movements and physical interactions of objects in space; astrophysical mathematics.
	is a kind of astrophysics
celestial pole	has definition One of two points at which the Earth's axis of rotation, if extended, would intersect the celestial sphere.
	has right ascension 0
	is a kind of equatorial coordinate
celestial sphere	has definition An imaginary sphere of arbitrary radius upon which celestial bodies may be considered to be located. As circumstances require, the celestial sphere may be centered at the observer, at the Earth's center or at any other location.
	is an instance of equatorial sky area
	is an instance of sphere
Celsius	has absolute zero -273.15
	has base unit K
	has boiling point of water 100
	has definition A mercury-in-glass temperature scale. The zero of the scale represents the melting point of ice and the boiling point of water is taken to be 100 degrees.
	has proposition date 1710
	has symbol °C
	has synonym Centigrade
	has triple point of water 0.01
	is an instance of named derived SI unit
	is an instance of temperature unit
	is named after Anders Celsius (1701-1744)
	to convert to Kelvin add 273.15
Cen X-1	is a part of Centaurus
	is an instance of transient X-ray source
Cen X-2	has definition sporadic X-ray source
	is a part of Centaurus
	is an instance of transient X-ray source
Cen X-4	has definition sporadic X-ray source
	is a part of Centaurus
	is an instance of X-ray source
cenozoic era	has duration 63 million years
	has start time 63 million years ago
	is a kind of geological era
Centaurus	has acronym Cen
	has genitive Centauri
	has historical origin the centaur Chiron which tutored Hercules and Jason
	has synonym Centaur
	is a part of celestial sphere
	is an instance of constellation
Centaurus A	has definition A strong radio source. Optically, it is an elliptical galaxy with a dark obscuring lane. It is the nearest known violent galaxy.
	has distance 4 Mpc
	has synonym 3U 1322-42
	has synonym NGC 5128
	is a part of Centaurus
	is an instance of radio source
	is an instance of X-ray source
Centaurus cluster	has definition A cluster of galaxies. Its radio counterpart is compact and located inside NGC 4696.
	has distance 200 Mpc
	has synonym 3U 1247-41
	is a part of Centaurus
	is a part of Local Supercluster
	is an instance of galaxy cluster
	is an instance of X-ray source
Centaurus X-3	has definition A pulsating binary X-ray source in the galactic plane. Optical component is Krzeminski's star, a B0 giant or supergiant. The X-ray component is probably a rotating neutron star of about 0.65-0.83 Msun. Cen X-3 is speeding up at a rate of about 1 part in 103-105 per year and will at this rate fall into its companion in about 1000 years.
	has distance 5-10 kpc
	has eclipse duration 0.488 days in X-ray
	has orbital eccentricity e < 0.002
	has orbital period 2.087 days
	has period 4.8 s
	has synonym 3U 1118-60
	has synonym Krzeminski's star
	is a part of Centaurus
	is an instance of eclipsing binary
	is an instance of X-ray pulsar
centi	has symbol c
	has value 10-2
	is an instance of unit prefix
central star of planetary nebula	has acronym CPN
	has synonym planerary nuclei
	is a kind of early star
Centre National d'Etudes Spatiales	has acronym CNES
	has location Paris, France
	is an instance of space science institution
Cep X-4	is a part of Cepheus
	is an instance of transient X-ray source
Cepheid	has definition A class of stars named after Delta Cephei which vary in brightness over a regular period of time (typically a few days). The period of change is directly related to the true, average brightness or luminosity of the star. Once the period is known the true brightness can be calculated and the distance estimated by observing the "apparent" brightness of the object as seen from Earth.
	has definition A type of variable star whose period of variation is tightly related to its intrinsic luminosity.
	has definition A yellow supergiant that pulsates, alternately brightening and dimming. Cepheids allow astronomers to measure distances, because the longer a Cepheid's period of variation, the greater the Cepheid's mean intrinsic brightness. To determine a Cepheid's distance, all an astronomer has to do is measure the Cepheid's period; comparing the star's mean intrinsic brightness with the star's mean apparent brightness then yields the distance. Cepheids are so bright that we can see them in other galaxies, allowing us to establish distances to entire galaxies beyond the Milky Way.
	has definition One of a group of very luminous supergiant pulsating stars. The luminosities of a Cepheid is proportional to its period, but a different P-L relation applies to each type. No Cepheid is near enough for an accurate trigonometric parallax (Polaris is the nearest). Cepheids are useful distance indicators to about 3 Mpc.
	has definition Strictly periodic variables with periods 1-50 days, of spectral types F, G and K.
	has period 1 to 50 days
	has prototype delta Cephei
	has spectral type F star, G star and K star
	is a kind of periodic variable
Cepheus	has acronym Cep
	has boundary
	has genitive Cephei
	has synonym Andromeda's Father
	has synonym King of Ethiopia
	is a part of celestial sphere
	is an instance of constellation
Cer-Vit	is a kind of mirror
Ceres	has definition Largest asteroid, and the first to be discovered.
	has discoverer Piazzi
	has discovery date 1801
	has eccentricity e = 0.079
	has inclination i = 10°.6
	has mass 1.17 × 1024 g
	has mean distance from Sun 2.7673 AU
	has mean orbital speed 17.9 km s-1
	has photographic albedo 0.06
	has radius R ≈ 510 km
	has rotation period 0.38 days
	has sidereal period 1682 days
	has surface spectra carbonaceous chondrite
	has synodic period 466.6 days
	is a part of asteroid belt
	is an instance of asteroid
cerium	has image
	has ocean oxidation state III
	has ocean residence time 100 years
	is a kind of rare Earth
	is a kind of scavenged oceanic element
CERN	has definition The European Laboratory for Particle Physics (formerly the Conseil Europeen pour la Recherche Nucleaire). Here, the resources of the European member nations are pooled to construct the large particle accelerators needed for high-energy experiments. The major facilities at CERN include the Super Proton Synchrotron (SPS) and the Large Electron-Positron (LEP) collider.
	has location near Geneva, Switzerland
	is an instance of high energy physics institution
cesium	has image
	has ocean oxidation state I
	has ocean residence time 600000 years
	is a kind of accumulating oceanic element
	is a kind of alkali metal
Cetus	has acronym Cet
	has genitive Ceti
	has historical image
	has historical origin the sea monster slain by Perseus to save Andromeda. Also known as the biblically famous whale who swallowed Jonah.
	has synonym Jonah's Whale
	has synonym Sea Monster
	is a part of celestial sphere
	is an instance of constellation
CGS unit	is a kind of unit
CH star	has definition G-type giant (G5 to K5) in which the molecular bands of CH are very strong.
	is a kind of G star
chalcophile element	has definition element that tends to concentrate in sulfides
	has occurrence in sulfide minerals
	is a kind of planetary element
Chamaeleon	has acronym Cha
	has genitive Chamaeleontis
	has synonym Chameleon
	is a part of celestial sphere
	is an instance of constellation named by Bayer
Chandra	has acronym AXAF
	has definition NASA's premier x-ray observatory
	is an instance of grazing-incidence telescope
	is named after Subrahmanyan Chandrasekhar
Chandrasekhar limit	has definition A limiting mass for white dwarfs. If the mass exceeds this critical mass (1.44 solar masses, for the expected mean molecular weight of 2), the load of the overlying layers will be so great that degeneracy pressure will be unable to support it, and no configuration will be stable.
	has definition The maximum mass, approximately 1.4 Msun, above which an object cannot support itself by electron degeneracy pressure; hence, the maximum mass of a white dwarf.
	is an instance of mass
Chandrasekhar-Schonberg limit	has definition Mass above which the helium core of a star begins to contract (eventually to collapse altogether). The limit is now reckoned as 10 to 15 per cent of the star's total mass.
	has definition The mass limit for an isothermal core. In order to maintain its luminosity by hydrogen burning just outside the isothermal core, the star must keep a high temperature and a high pressure at the surface of the core. When the helium core exceeds about 12% of the star's total mass, the star can no longer adjust by small changes, but must drastically increase in radius and move rapidly from the main sequence.
	is an instance of mass
characteristic impedance of vacuum	has symbol Z0
	has uncertainty 0
	has unit Ω
	has value 376.730313461 Ω
	is an instance of resistance
	is an instance of universal constant
charge	has definition The fundamental property of a particle that causes it to be affected by the electromagnetic force.
	has unit charge unit
	has unit charge unit
	is a kind of electromagnetic quantity
	is a kind of electromagnetic quantity
charge multiplet	has definition A group of particles which differ in electrical charge but which are nearly identical in mass and other respects (such as lifetime and angular momentum) and which seem to experience identical nuclear forces.
	has lifetime -has source: [H76]
	has mass -has source: [H76]
	has spin -has source: [H76]
	is a kind of hadron
charge unit	is a kind of electromagnetic unit
	is a unit of charge
charge-coupled device	has acronym CCD
	has definition A small photoelectronic imaging device (typically 1.5 cm square) made from a crystal of semiconductor silicon in which numerous (at least 250000) individual light-sensitive picture elements (pixels) have been constructed. Each tiny pixel (less than 0.03 mm in size) is capable of storing electronic charges created by the absorption of light. The name derives from the method of extracting the locally stored charges from each pixel which is done by transferring or "coupling" charges from one pixel to the next by the controlled collapse and growth of adjacent storage sites or "potential wells". Each "well" is formed inside the silicon crystal by the electric field generated by voltages applied to tiny, semi-transparent metallic electrodes on the CCD surface.
	has definition Highly sensitive photoelectric devices that can electronically record the intensity and point of arrival of tiny amounts of light. CCDs are placed at the receiving end of telescopes, to "take pictures" of very faint astronomical objects; they have almost completely replaced photographic plates.
	is a kind of integrating detector
charged particle	has charge non-zero
	has definition A particle with non-zero charge
	is a kind of particle
	is accelerated by electric or magnetic fields
Charles's law	has definition The pressure of an ideal gas at constant volume varies directly as the absolute temperature.
	is an instance of gas law
charm	has charge 2/3
	has definition The fourth flavor (i.e. type) of quark, the discovery of which in 1974 contributed both to the acceptance of the reality of quarks and to our understanding of their dynamics. The charmed quark exhibits a property called "charm" which is conserved in strong interactions.
	has definition The fourth flavor of quarks. Predicted by theory, charmed quarks were discovered in 1974.
	has definition The property that distinguishes one of the types of quarks. At present, there are six types of quarks known, one of which is the "charmed" quark. (See quark.)
	is an instance of heavy quark
chemical process	has domain chemistry
	is a kind of process
chemistry	has definition The scientific study of chemicals and chemical reactions.
	is a kind of science
Cherenkov detector	has definition Apparatus through which it is possible to observe the existence and velocity of high-speed particles important in experimental nuclear physics and in the study of cosmic radiation. It was originally built to investigate the Cherenkov radiation effect, in which charged particles travel through a medium at a speed greater than that of light in that medium.
	is a kind of high energy detector
Chi squared test	has definition A least-squares statistical test that measures the probability of randomness in a distribution.
	has symbol χ2
	is an instance of statistical test
chirality	has definition An expression of the basic handedness of nature. Fundamental theories of the elementary particles and of superstrings must possess chirality.
	has definition Feature of fundamental particle physics that distinguishes left- from right-handed, showing that the universe is not fully left-right symmetric.
	has synonym chiral
	is an instance of quantum quantity
chlorine	has abundance 130 p.p.m. in Earth's crust
	has abundance 18000 p.p.m. in seawater
	has abundance 3.2 × 105 in Sun relative to H = 1 × 1012
	has atomic emission line 479.455 nm for Cl II
	has atomic emission line 489.677 nm for Cl II
	has atomic emission line 542.323 nm for Cl II
	has atomic emission line 858.597 nm for Cl I
	has atomic emission line 837.574 nm for Cl I (strong)
	has atomic number 17
	has biological role chloride, Cl-, is essential to many species, including humans
	has boiling point 239.18 K
	has chief source halite (rock salt)
	has covalent radii 99 pm
	has critical pressure 7700 kPa
	has critical temperature 417 K
	has crystal cell dimension a = 856, c = 612 pm
	has crystal type tetragonal
	has daily dietary intake 3.00 - 6.50 g
	has definition yellow-green, dense, sharp-smelling gas (Cl2) which is a key industrial chemical
	has density 1507 kg m-3 for liquid at 239.18 K boiling point
	has density 2030 kg m-3 for solid at 113 K
	has density 3.214 kg m-3 for gas at 273 K
	has discoverer C.W. Scheele
	has discovery date 1774
	has discovery location Uppsala, Sweden
	has electron affinity 349.0 kJ mol-1 from Cl to Cl-
	has electron configuration [Ne]3s23p5 in ground state
	has electronegativity 3.16 Pauling
	has hazard Cl2 0.5 p.p.m. time-weighted average above which there is a threat to health
	has hazard Cl2 15 p.p.m. produces throat irritation
	has hazard Cl2 50 p.p.m. is dangerous even in short doses
	has hazard corrosive, vapours attack eyes and lungs
	has heat capacity 21.840 J K-1 mol-1 for atomic gas at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 33.907 J K-1 mol-1 for molecular gas (Cl2) at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 6.41 kJ mol-1
	has heat of vaporization 20.4033 kJ mol-1
	has image
	has ionic radii 181 pm for Cl-
	has isotope mass range 31 to 41
	has lethal intake Cl2 inhalation 500 p.p.m. for 5 minutes for humans
	has level in humans 2000 - 5200 p.p.m. chloride in muscle
	has level in humans 2890 mg dm-3 chloride in blood
	has level in humans 3000 - 7200 p.p.m. chloride in liver
	has level in humans 900 p.p.m. chloride in bone
	has longest lived isotope chlorine 35
	has main mining area vast deposits in USA, Poland, Russia, Germany, China, India, Australia
	has mass absorption coefficient 106 cm2 g-1 for CuKα X-ray diffraction
	has mass absorption coefficient 11.4 cm2 g-1 for MoKα X-ray diffraction
	has mass magnetic susceptibility -7.2 × 10-9 kg-1 m3 for gas
	has mass of element in person 95 g for a 70 kg average person
	has melting point 172.17 K
	has mineral halite, carnallite, sylvite
	has molar volume 17.46 cm3 for solid at 113 K
	has name origin chloros = pale green from Greek
	has neutron scattering length 0.95770 × 10-12 cm
	has number of isotopes 13 including nuclear isomers
	has number of protons 17
	has ocean oxidation state -I
	has ocean residence time 4 × 108 years
	has pronunciation klor-een
	has registry number 7782-50-5 for Chemical Abstracts System database
	has relative atomic mass 35.4527 in units of 12C = 12.000
	has reserves > 1 × 1013 tonnes
	has space group P4/ncm
has specimen Cl2 in small pressurized canisters. Danger!
has symbol Cl
has synthesis mechanism electrolysis of sodium chloride solution
has term symbol 2P3/2 in ground state
has thermal conductivity 0.0089 W m-1 K-1 for gas at 300 K
has thermal neutron capture cross section 35.5 barns
has toxic intake Cl2 is very toxic affecting the eyes and lungs at 3 p.p.m. in air; chloride is non-toxic
has uses bleaching agent
has uses manufacture of organochlorine solvents
has uses PVC
has uses sterilising agent for water supplies
has van der Waals radii 181 pm
has world production 168 × 106
is a kind of accumulating oceanic element
is a kind of gaseous element
is a kind of halogen
is a kind of lithophile element
chlorine 34m	has atomic mass 33.973763
	has decay mode β+
	has decay mode γ
	has decay mode IT
	has half life 32.2 minutes
	has nuclear spin I = 3+ h/2π
	has number of neutrons 17
	has number of nucleons 34
	has symbol 34Cl
	is an instance of chlorine
chlorine 35	has atomic mass 34.968852721
	has magnetogyric ratio 2.6210 × 107 rad T-1 s-1
	has natural abundance 75.77%
	has NMR frequency 9.798 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 20.2 where 13C = 1.00
	has nuclear magnetic moment μ = +0.8218736 nuclear magnetons with diamagnetic correction
	has nuclear quadrupole moment -0.08165 × 10-28 m2
	has nuclear spin I = 3/2+ h/2π
	has number of neutrons 18
	has number of nucleons 35
	has relative NMR sensitivity 4.70 × 10-3 where 1H = 1.00
	has symbol 35Cl
	has uses isotopically enriched samples available for experimental purposes
	has uses Nuclear Magnetic Resonance
	is an instance of chlorine
chlorine 36	has atomic mass 35.968306
	has decay mode β+
	has decay mode β- (0.709 Mev)
	has decay mode EC (1.142 Mev)
	has decay mode no γ
	has half life 3.01 × 107 years
	has nuclear magnetic moment μ = +1.28547 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 2+ h/2π
	has number of neutrons 19
	has number of nucleons 36
	has symbol 36Cl
	has uses research
	is an instance of chlorine
chlorine 37	has atomic mass 36.96590262
	has magnetogyric ratio 2.1718 × 107 rad T-1 s-1
	has natural abundance 24.23%
	has NMR frequency 8.156 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 3.8 where 13C = 1.00
	has nuclear magnetic moment μ = +0.6841230 nuclear magnetons with diamagnetic correction
	has nuclear quadrupole moment -0.06435 × 10-28 m2
	has nuclear spin I = 3/2+ h/2π
	has number of neutrons 37
	has number of nucleons 20
	has relative NMR sensitivity 2.71 × 10-3 where 1H = 1.00
	has symbol 37Cl
	has uses isotopically enriched samples available for experimental purposes
	has uses Nuclear Magnetic Resonance
	is an instance of chlorine
chlorine 38	has atomic mass 37.968010
	has decay mode β- (4.917 Mev)
	has decay mode γ
	has half life 37.2 minutes
	has nuclear magnetic moment μ = 2.05 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 2- h/2π
	has number of neutrons 21
	has number of nucleons 38
	has symbol 38Cl
	is an instance of chlorine
chlorine 39	has atomic mass 38.968005
	has decay mode β- (3.44 Mev)
	has decay mode γ
	has half life 55.6 minutes
	has nuclear spin I = 3/2- h/2π
	has number of neutrons 22
	has number of nucleons 39
	has symbol 39Cl
	is an instance of chlorine
chlorine 40	has atomic mass 39.970440
	has decay mode β- (7.5 Mev)
	has decay mode γ
	has half life 1.38 minutes
	has nuclear spin I = 2- h/2π
	has number of neutrons 23
	has number of nucleons 40
	has symbol 40Cl
	is an instance of chlorine
chromium	has abundance 1.5 × 10-4 p.p.m. in Pacific surface seawater
	has abundance 1.8 × 10-4 p.p.m. in Atlantic surface seawater
	has abundance 100 p.p.m. in Earth's crust
	has abundance 2.3 × 10-4 p.p.m. in deep Atlantic seawater
	has abundance 2.5 × 10-4 p.p.m. in deep Pacific seawater
	has abundance 5.13 × 105 in Sun relative to H = 1 × 1012
	has atomic emission line 357.869 nm for Cr I (used in atom absorption spectrometry)
	has atomic emission line 359.349 nm for Cr I
	has atomic emission line 360.533 nm for Cr I
	has atomic emission line 427.480 nm for Cr I
	has atomic emission line 428.972 nm for Cr I
	has atomic emission line 520.844 nm for Cr I
	has atomic emission line 425.435 nm for Cr I (strong)
	has atomic number 24
	has atomic radii 125 pm
	has biological role essential to some species, including humans, stimulates metabolism
	has boiling point 2945 K
	has bulk modulus 160.2 GPa
	has chief source chromite
	has crystal cell dimension a = 288.46 pm
	has crystal type b.c.c.
	has daily dietary intake 0.01 - 1.2 mg
	has definition hard, blue-white metal which resists oxidation in air, can be polished to a high shine
	has density 6460 kg m-3 for liquid at 2130 K melting point
	has density 7190 kg m-3 for solid at 293 K
	has discoverer Nicholas Louis Vauquelin
	has discovery date 1780
	has discovery location Paris, France
	has electrical resistivity 12.7 × 10-8 Ω m at 293 K
	has electron affinity 64.3 kJ mol-1 from Cr to Cr-
	has electron configuration [Ar]3d54s1 in ground state
	has electronegativity 1.66 Pauling
	has hazard poison by ingestion, suspected carcinogen, chromates are corrosive to tissue
	has heat capacity 20.79 J K-1 mol-1 for gas at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 23.35 J K-1 mol-1 for solid at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 15.3 kJ mol-1
	has heat of vaporization 348.78 kJ mol-1
	has image
	has ionic radii 56 pm for Cr4+
	has ionic radii 64 pm for Cr3+
	has ionic radii 84 pm for Cr2+
	has isotope mass range 45 to 57
	has lethal intake 70 mg kg-1 metal taken oraly in humans
	has level in humans 0.006 - 0.11 mg dm-3 in blood
	has level in humans 0.02 - 3.3 p.p.m. in liver
	has level in humans 0.024 - 0.84 p.p.m. in muscle
	has level in humans 0.1 - 0.33 p.p.m. in bone
	has linear expansion coefficient 6.2 × 10-6 K-1
	has longest lived isotope chromium 52
	has main mining area Turkey, South Africa, Zimbabwe, Russia, Philipipines
	has mass absorption coefficient 260 cm2 g-1 for CuKalpha X-ray diffraction
	has mass absorption coefficient 31.1 cm2 g-1 for MoKalpha X-ray diffraction
	has mass magnetic susceptibility +4.45 × 10-8 kg-1 m3 for solid
	has mass of element in person 14 mg for a 70 kg average person
	has melting point 2130 ± 20 K
	has mineral chromite, crocoite
	has molar volume 7.23 cm3
	has name origin chroma = colour from Greek
	has neutron scattering length 0.3635 × 10-12 cm
	has number of isotopes 13 including nuclear isomers
	has number of protons 24
	has ocean oxidation state VI
	has ocean residence time 10000 years
	has poisson's ratio 0.21 GPa
has pronunciation kroh-mi-uhm
has registry number 7440-47-3 for Chemical Abstracts System database
has relative atomic mass 51.9961 in units of 12C = 12.000
has reserves 1 × 109 tonnes
has rigidity modulus 115.3 GPa
has space group Im3m
has specimen chips, chunks, crystallites or powder. Safe.
has symbol Cr
has term symbol 7S3 in ground state
has thermal conductivity 93.7 W m-1 K-1 at 300 K
has thermal neutron capture cross section 3.1 barns
has toxic intake 200 mg
has uses alloys, plating and metal ceramics
has world production 20000 tonnes year-1 for chromium metal
has world production 9.6 × 106 tonnes year-1 for chromite ore
has young's modulus 279 GPa
is a kind of chalcophile element
is a kind of recycled oceanic element
is a kind of transition metal
reacts with HCL and H2SO4 by disolving
chromium 48	has atomic mass 47.954033
	has decay mode γ
	has decay mode EC (1.65 Mev)
	has half life 21.6 hours
	has number of neutrons 24
	has number of nucleons 48
	has symbol 48Cr
	is an instance of chromium
chromium 49	has atomic mass 48.951338
	has decay mode β+
	has decay mode γ
	has decay mode EC (2.627 Mev)
	has half life 42.3 minutes
	has nuclear magnetic moment μ = 0.476 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 5/2- h/2π
	has number of neutrons 25
	has number of nucleons 49
	has symbol 49Cr
	is an instance of chromium
chromium 50	has atomic mass 49.9460464
	has natural abundance 4.345%
	has nuclear spin I = 0+ h/2π
	has number of neutrons 26
	has number of nucleons 50
	has symbol 50Cr
	has uses isotopically enriched samples available for experimental purposes
	is an instance of chromium
chromium 51	has atomic mass 50.944768
	has decay mode γ
	has decay mode EC (0.751 Mev)
	has half life 27.70 days
	has nuclear magnetic moment μ = -0.934 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 7/2- h/2π
	has number of neutrons 27
	has number of nucleons 51
	has symbol 51Cr
	has uses medical diagnostic
	has uses research
	is an instance of chromium
chromium 52	has atomic mass 51.9405098
	has natural abundance 83.789%
	has nuclear spin I = 0+ h/2π
	has number of neutrons 28
	has number of nucleons 52
	has symbol 52Cr
	has uses isotopically enriched samples available for experimental purposes
	is an instance of chromium
chromium 53	has atomic mass 52.9406513
	has magnetogyric ratio -1.5120 × 107 rad T-1 s-1
	has natural abundance 9.501%
	has NMR frequency 5.652 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 0.49 where 13C = 1.00
	has nuclear magnetic moment μ = -0.47454 nuclear magnetons with diamagnetic correction
	has nuclear quadrupole moment -0.150 × 10-28 m2
	has nuclear spin I = 3/2- h/2π
	has number of neutrons 29
	has number of nucleons 53
	has relative NMR sensitivity 9.03 × 10-4 where 1H = 1.00
	has symbol 53Cr
	has uses isotopically enriched samples available for experimental purposes
	has uses Nuclear Magnetic Resonance
	is an instance of chromium
chromium 54	has atomic mass 53.9388825
	has natural abundance 2.365%
	has nuclear spin I = 0+ h/2π
	has number of neutrons 30
	has number of nucleons 54
	has symbol 54Cr
	has uses isotopically enriched samples available for experimental purposes
	is an instance of chromium
chromium 55	has atomic mass 54.940842
	has decay mode β- (2.603 Mev)
	has decay mode γ
	has half life 3.497 minutes
	has nuclear spin I = 3/2- h/2π
	has number of neutrons 31
	has number of nucleons 55
	has symbol 55Cr
	is an instance of chromium
chromium 56	has atomic mass 55.940643
	has decay mode β- (1.62 Mev)
	has decay mode γ
	has half life 5.9 minutes
	has nuclear spin I = 0+ h/2π
	has number of neutrons 32
	has number of nucleons 56
	has symbol 56Cr
	is an instance of chromium
chromosphere	has definition The part of the solar atmosphere between the photosphere and the corona. It consists of two rather well defined zones: the lower chromosphere and the upper chromosphere.
	has definition The part of the Sun's atmosphere immediately above the surface (the photosphere) and beneath the corona.
	has has density ρ ≈ 10-16 to 10-8 g cm-3
	is a part of solar atmosphere
chromospheric network	has definition A large-scale cellular pattern along the boundaries of which lie bright and dark mottles seen in Hα and other regions.
	is a part of chromosphere
Circinus	has acronym Cir
	has genitive Circini
	has synonym Compass
	is a part of celestial sphere
	is an instance of constellation named by de Lacaille
Circinus X-1	has definition A highly variable X-ray source. Many of its properties are similar to those of Cygnus X-1.
	has synonym 3U 1516-56
	is a part of Circinus
	is an instance of X-ray source
circle	has definition An ellipse possessing but one focus.
	is a kind of ellipse
circumpolar region	has coordinates whose equatorial latitude is greater than the Earth latitude of the observer minus 90 degrees
	has definition a region defined by an equatorial latitude above which stars are visible all year (depends on observers location on Earth)
	has purpose to define a part of the sky which can be observed all year at the observers location
	is a part of celestial sphere
	is an instance of equatorial sky area
circumpolar star	has definition Star which never sets, from the viewpoint of an observer on Earth.
	is a kind of star
class I globular cluster	is a kind of globular cluster
class II globular cluster	is a kind of globular cluster
class III globular cluster	is a kind of globular cluster
class IV globular cluster	is a kind of globular cluster
class IX globular cluster	is a kind of globular cluster
class V globular cluster	is a kind of globular cluster
class VI globular cluster	is a kind of globular cluster
class VII globular cluster	is a kind of globular cluster
class VIII globular cluster	is a kind of globular cluster
class X globular cluster	is a kind of globular cluster
class XI globular cluster	is a kind of globular cluster
classical electron radius	has equation
	has symbol re
	has uncertainty 0.00000031 × 10-15 m
	has value 2.817940285 × 10-15 m
	is an instance of atomic constant
	is an instance of radius
classical nova	has initial rise of light curve typically 12 magnitudes
	has rate of decline of light curve which is nearly exponential
	has rate of decline of light curve which is proportional to the absolute magnitude at maximum (can be used as a distance measureing technique)
	has ultraviolet flux light curve which increases after optical maximum
	is a kind of nova
classical physics	has definition Physics prior to the introduction of the quantum principle. Classical physics incorporates Newtonian mechanics, views energy as a continuum, and is strictly causal.
	is a kind of physics
close binary	is a kind of binary star
closed string	has definition A type of string that is in the shape of a loop.
	is a kind of string theory
closed universe	has definition A homogeneous, isotropic universe is said to be temporally closed if gravity is strong enough to eventually reverse the expansion, causing the universe to recollapse. It is said to be spatially closed if gravity is strong enough to curve the space back on itself, forming a finite volume with no boundary. Triangles would contain more than 180°, the circumference of a circle would be less than π times the diameter, and a traveler intending to travel in a straight line would eventually find herself back at her starting point. If Einstein's cosmological constant is zero, as is frequently assumed, then a universe which is temporally closed is also spatially closed, and vice versa.
	has definition A standard universe with a spherical three-dimensional spatial geometry. Such a universe is finite in both space and time, and recollapses.
	has definition A universe that has a finite size. Closed universes expand for a finite time, reach a maximum size, and then collapse. In closed universes, the inward pull of gravity dominates and eventually reverses the outward flying apart of matter; that is, gravitational energy dominates the kinetic energy of expansion. The value of omega is greater than 1 for a closed universe. If a universe begins closed, it remains closed; if it begins open, it remains open; if it begins flat, it remains flat. In the big bang model of the universe, the question of whether the universe is closed, open, or flat is determined by the initial conditions, just as the fate of a rocket launched from earth is determined by its initial upward velocity relative to the strength of earth's gravitational pull. If the initial rate of expansion of the universe was lower than a critical value, determined by the mass density, the universe will expand only for a certain period of time and then collapse, just as a rocket launched with a velocity below a critical value, dependent on the strength of earth's gravity, will reach a maximum height and then fall back to earth. This is the behavior of a closed universe. If the initial rate of expansion of the universe was larger than a critical value, the universe is open and will keep expanding forever. If the initial rate of expansion was precisely the critical value, the universe is flat and will expand forever, but with a rate of expansion that approaches zero. (See flat universe; omega; open universe.)
	has definition Any model of the Universe in which the gravity of the matter content can reverse the expansion and cause a collapse.
	has definition Big Bang model that was formulated by Friedmann and Lemaitre which has a positive curvature, like the surface of a sphere, in which case the universe is finite, closed, and will eventually recollapse. This space is unbounded.
	has definition Cosmological model in which the universe eventually stops expanding and begins to collapse, presumably to end in a fireball like that of the big bang. Compare open universe.
	has geometry of space positive curvature
	is a kind of big bang
CN-strong star	has definition Late type giant with strong CN bands. Metallic lines are also stronger than in normal giants.
	is a kind of giant
	is a kind of late star
CN-weak star	has definition High-velocity star with both weak metallic lines and weak CN bands.
	is a kind of weak line star
CNO bi-cycle	has definition Similar to the CNO cycle, except that it also includes a cycle in which the next-to-last step becomes 15N(p, γ) 16O(p, γ) 17F(β+ν) 17O(p, α) 14N. This reaction occurs once in about 2000 CN cycles. For main-sequence stars greater than a few solar masses, hydrogen burning by the CNO bi-cycle is the main source of energy.
	has probability 2% of the energy of our Sun
	is an instance of carbon cycle
CNO tri-cycle	has definition Similar to the CNO bi-cycle, with the addition of the cycle 17O(p, γ) 18F(β+ν) 18O(p, α) 15N.
	is an instance of carbon cycle
co-moving coordinate	has definition A set of coordinates which do not change in an expanding (or otherwise moving) medium. i.e. the coordinates of a distant galaxy do not change just because of the expansion of space.
	has definition Coordinates fixed with respect to the overall Hubble flow of the universe, so that they do not change as the universe expands.
	is a kind of coordinate
Coalsack	has definition A prominent dark nebula readily visible to the naked eye, located on the galactic plane.
	has distance 170 pc
	is a part of Crux
	is a part of dust
	is an instance of dark nebula
coating	is a kind of optical device
cobalt	has abundance 1.1 × 10-6 p.p.m. in deep Pacific seawater
	has abundance 20 p.p.m. in Earth's crust
	has abundance 6.9 × 10-6 p.p.m. in Pacific surface seawater
	has abundance 7.94 × 104 in Sun relative to H = 1 × 1012
	has atomic emission line 240.725 nm for Co I (used in atom absorption spectrometry)
	has atomic emission line 242.493 nm for Co I
	has atomic emission line 340.512 nm for Co I
	has atomic emission line 344.364 nm for Co I
	has atomic emission line 350.228 nm for Co I
	has atomic emission line 356.938 nm for Co I
	has atomic emission line 345.350 nm for Co I (strong)
	has atomic number 27
	has atomic radii 125 pm
	has biological role essential to most species, including humans
	has boiling point 3143 K
	has bulk modulus 181.5 GPa
	has chief source cobaltite, skutterudite
	has covalent radii 116 pm
	has crystal cell dimension a = 250.7, c = 406.9 pm for ε-Co
	has crystal cell dimension a = 354.41 pm for α-Co
	has crystal type f.c.c. for α-Co
	has crystal type h.c.p. for ε-Co
	has daily dietary intake 0.005 - 1.8 mg
	has definition lustrous, silvery-blue, hard metal which is also ferromagnetic. Cobalt 60 is an important radioisotope
	has density 7670 kg m-3 for liquid at 293 K at melting point
	has density 8900 kg m-3 for solid at 293 K
	has discoverer Georg Brandt
	has discovery date 1735
	has discovery location Stockholm, Sweden
	has electrical resistivity 6.24 × 10-8 Ω m at 293 K
	has electron affinity 63.8 kJ mol-1 from Co to Co-
	has electron configuration [Ar]3d74s2 in ground state
	has electronegativity 1.88 Pauling
	has hazard compounds have low toxicity when ingested, but produce vomiting. Suspected carcinogen.
	has heat capacity 23.020 J K-1 mol-1 for gas at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 24.81 J K-1 mol-1 for solid at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 15.2 kJ mol-1
	has heat of vaporization 382.4 kJ mol-1
	has image
	has ionic radii 64 pm for Co3+
	has ionic radii 82 pm for Co2+
	has isotope mass range 35m to 64
	has lethal intake 80 mg kg-1 chloride ingested by rat
	has level in humans 0.0002 - 0.04 mg dm-3 in blood
	has level in humans 0.01 - 0.04 p.p.m. in bone
	has level in humans 0.028 - 0.65 p.p.m. in muscle
	has level in humans 0.06 - 1.1 p.p.m. in liver
	has linear expansion coefficient 13.36 × 10-6 K-1
	has longest lived isotope cobalt 59
	has main mining area Zaire, Morocco, Sweden, Canada
	has mass absorption coefficient 313 cm2 g-1 for CuKalpha X-ray diffraction
	has mass absorption coefficient 42.5 cm2 g-1 for MoKalpha X-ray diffraction
	has mass magnetic susceptibility ferromagnetic
	has mass of element in person 3 mg for a 70 kg average person
	has melting point 1768 K
	has mineral cobaltite, erythrite, glaucodot, linnaerite, skutterudite (smaltite)
	has molar volume 6.62 cm3
	has name origin kobald = goblin from German
	has neutron scattering length 0.278 × 10-12 cm
	has number of isotopes 17 including nuclear isomers
	has number of protons 27
	has ocean oxidation state II
	has ocean residence time 40 years
	has poisson's ratio 0.32 GPa
has pronunciation koh-bolt
has registry number 7440-48-4 for Chemical Abstracts System database
has relative atomic mass 58.93320 in units of 12C = 12.000
has rigidity modulus 82 GPa
has space group Fm3m for α-Co
has space group P63/mmc for ε-Co
has specimen foil, pieces, powder, rod and wire. Care !
has symbol Co
has term symbol 4F9/2 in ground state
has thermal conductivity 100 W m-1 K-1 at 300 K
has thermal neutron capture cross section 37.2 barns
has toxic intake 500 mg
has uses magnet alloys, ceramics, catalysts and paints
has world production 17000 tonnes year-1
has young's modulus 211 GPa
is a kind of scavenged oceanic element
is a kind of siderophile element
is a kind of transition metal
reacts with dilute acids
cobalt 55	has atomic mass 54.942001
	has decay mode β+ (3.452 Mev)
	has decay mode γ
	has decay mode EC
	has half life 17.53 hours
	has nuclear magnetic moment μ = +4.822 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 7/2- h/2π
	has number of neutrons 28
	has number of nucleons 55
	has symbol 55Co
	is an instance of cobalt
cobalt 56	has atomic mass 55.939841
	has decay mode β+ (4.566 Mev)
	has decay mode γ
	has decay mode EC
	has half life 77.3 days
	has nuclear magnetic moment μ = +3.85 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 4+ h/2π
	has number of neutrons 29
	has number of nucleons 56
	has symbol 56Co
	is an instance of cobalt
cobalt 57	has atomic mass 56.936294
	has decay mode γ
	has decay mode EC (0.836 MeV)
	has half life 271.8 days
	has nuclear magnetic moment μ = +7.72 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 7/2- h/2π
	has number of neutrons 30
	has number of nucleons 57
	has symbol 57Co
	has uses medical diagnosis
	has uses research
	is an instance of cobalt
cobalt 58	has atomic mass 57.935755
	has decay mode β+ (2.30 Mev)
	has decay mode γ
	has decay mode EC
	has half life 70.88 days
	has nuclear magnetic moment μ = +4.04 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 2+ h/2π
	has number of neutrons 31
	has number of nucleons 58
	has symbol 58Co
	has uses medical diagnosis
	has uses research
	is an instance of cobalt
cobalt 59	has atomic mass 58.9331976
	has magnetogyric ratio 6.3472 × 107 rad T-1 s-1
	has natural abundance 100%
	has NMR frequency 23.614 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 1570 where 13C = 1.00
	has nuclear magnetic moment μ = +4.627 nuclear magnetons with diamagnetic correction
	has nuclear quadrupole moment +0.420 × 10-28 m2
	has nuclear spin I = 7/2- h/2π
	has number of neutrons 32
	has number of nucleons 59
	has relative NMR sensitivity 0.28 where 1H = 1.00
	has symbol 59Co
	has uses Nuclear Magnetic Resonance
	is an instance of cobalt
cobalt 60	has atomic mass 59.933819
	has decay mode β- (2.824 Mev)
	has decay mode γ
	has half life 5.27 years
	has nuclear magnetic moment μ = +3.799 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 5+ h/2π
	has number of neutrons 33
	has number of nucleons 60
	has symbol 60Co
	has uses medical diagnosis
	has uses medical therapy
	has uses research
	is an instance of cobalt
cobalt 61	has atomic mass 60.932478
	has decay mode β- (1.322 Mev)
	has decay mode γ
	has half life 1.650 hours
	has nuclear spin I = 7/2- h/2π
	has number of neutrons 34
	has number of nucleons 61
	has symbol 61Co
	is an instance of cobalt
coherent scattering	has definition A scattering process that leaves atoms in the same energy state after the scattered photon departs in a direction different from that of the incident photon. The energy of the scattered photon is the same (in the rest frame of the atom) as that of the incident photon.
	is a kind of scattering
cold dark matter	has acronym CDM
	has definition A model of structure formation in which an exotic particle whose energy is low at the time it decouples from other matter is responsible for structure formation.
	has definition Any dark matter candidate which was non-relativistic at the point of decoupling.
	has definition Hypothetical subatomic particles that move slowly compared with the speed of light.
	is a kind of dark matter
collapse	has definition Sudden contraction of a celestial body
	is a kind of contraction
collection of galaxies	has number of galaxies
	is a kind of collection of stars
collection of particles	is a kind of natural object
collection of stars	has catalog catalog about star systems
	has definition Two or more stars forming a gravitationally bound system
	has number of stars
	is a kind of celestial body
collider	has definition A particle accelerator in which beams of particles with equal but opposite momentum are made to collide head on.
	is a kind of particle accelerator
collision	is a kind of atomic process
color	is a kind of radiation measurement
color temperature	has definition A stellar temperature determined by comparison of the spectral distribution of the star's radiation with that of a blackbody.
	is a kind of temperature
Columba	has acronym Col
	has genitive Columbae
	has historical image
	has synonym Dove
	is a part of celestial sphere
	is an instance of constellation formerly part of Argo Navis
column grouped element	has group a column number in the table of the elements
	is a kind of element
coma	has definition The spherical region of diffuse gas, about 150000 km in diameter, which surrounds the nucleus (q.v.) of a comet. Together, the coma and the nucleus form the comet's head.
	has synonym comet head
	is a part of comet
Coma Berenices	has acronym Com
	has boundary
	has genitive Comae Berenices
	has historical image
	has synonym Berenice's Hair
	is a part of celestial sphere
	is an instance of constellation
Coma cluster	has definition The nearest massive cluster of galaxies. A symmetric cluster with primarily E and S0 galaxies. Luminous mass 4 × 1014 Msun = 8 × 1047 g; virial theorem mass about 5 × 1048 g; mass needed to bind the cluster about 4 × 1049 g. R ≈ 9 × 1024 cm.
	has diameter 10 million light years
	has distance 300 million light years
	has mass 4 × 1014 Msun (luminous matter)
	has number of galaxies 1000
	has redshift z = 0.023
	has synonym Abell 1656
	has synonym Coma X-1
	is a part of Coma Berenices
	is a part of Local Supercluster
	is an instance of rich cluster
	is an instance of X-ray source
Coma open cluster	has definition Open cluster similar to the Hyades in overall binary frequency.
	has distance 80 pc
	has number of stars 100
	is a part of Coma Berenices
	is a part of disk
	is an instance of open cluster
Coma X-1	has definition An extended X-ray source in the Coma cluster of galaxies.
	has synonym 3U 1257+28
	is a part of Coma Berenices
	is a part of Coma cluster
	is an instance of X-ray source
comet	has definition A diffuse body of gas and solid particles (such as CN, C2, NH3, and OH), which orbits the Sun. The orbit is usually highly elliptical or even parabolic (average perihelion distance less than 1 AU; average aphelion distance, roughly 104 AU). Comets are unstable bodies with masses on the order of 1018 g whose average lifetime is about 100 perihelion passages. Periodic comets comprise only about 4% of all known comets. Comets are obviously related in some manner to meteors, but no meteorites from a comet have ever been recovered. Observations of comets Bennett and Kohoutek have established that a comet is surrounded by a vast hydrogen halo.
	is a kind of celestial body
	is a part of our solar system
comet impact	is a kind of impact event
comet nucleus	has definition The stellar-appearing frozen core, containing almost the entire cometary mass, in the head of a comet.
	is a part of comet
comet tail	has definition The long streamer behind the comet head which does not usually appear until the comet is inside the orbit of Mars.
	has density 10-18 atm
	has length 107 km
	has mean distance from Sun inside the orbit of Mars
	is a part of comet
cometary nebula	has definition A reflection nebula with a fan shape that bears a superficial resemblance to a comet. Classical examples of the heads of cometary nebulae are R Mon, R CrA, and RY Tau. All have A0-G0 type spectra that resemble the spectrum of a T Tauri star, and their brightness varies from year to year.
	is a kind of reflection nebula
commensurate orbit	has definition A term applied to two bodies orbiting around a common barycenter when the period of one is an integral multiple of that of the other.
	has period an integral multiple of that of the other body
	is a kind of elliptical orbit
communication satellite	is a kind of artificial satellite
compact galaxy	has definition A galaxy similar to an N galaxy but with no disk or nebulous background. It is an object of high surface brightness which appears slightly nonstellar on photographs and which has a larger redshift than normal stars in our Galaxy. Nearest "compact" galaxy is M32.
	is a kind of galaxy
compact group	has definition Galaxy group with a few galaxies separated by a few galaxy diameters.
	has number of galaxies < 10
	is a kind of galaxy group
compact H II region	has definition A dense (ne ≥ 103 cm-3) H II region of small linear dimensions (≤ 1 pc).
	is a kind of H II region
composite spectrum star	has definition Object with a spectrum due to superposition of the spectra of two different stars.
	is a kind of star
Compton	is an instance of X-ray space telescope
Compton scattering	has antonym inverse Compton effect
	has definition Decrease in the frequency of high-energy radiation (such as X-rays) caused when a photon loses some of its energy to a free electron by collision.
	has definition Scattering of a photon due to the Compton effect (see also noncoherent scattering).
	has definition The scattering of photons by free electrons in an ionized medium.
	is a kind of scattering
condensation	has definition from gas to liquid or from gas to solid
	has final phase liquid
	has initial phase gas
	has inverse process evaporation
	is a kind of first order phase transition
conductance	has unit conductance unit
	is a kind of electromagnetic quantity
conductance quantum	has equation
	has symbol G0
	has uncertainty 0.000000028 × 10-5 S
	has value 7.748091696 × 10-5 S
	is an instance of conductance
	is an instance of electromagnetic constant
conductance unit	is a kind of electromagnetic unit
	is a unit of conductance
conic section	has dimensions 2
	is a kind of geometrical object
conjunction	has definition The phenomenon in which two bodies have the same apparent celestial longitude (see longitude, celestial) or right ascension as viewed from a third body. Conjunctions are usually tabulated as geocentric phenomena. For Mercury and Venus, geocentric inferior conjunction occurs when the planet is between the Earth and Sun, and superior conjunction occurs when the Sun is between the planet and Earth.
	has elongation 0°
	is a kind of planetary elongation event
conservation law	has definition A quantity that remains unchanged in the course of the evolution of a dynamical system. There are seven known quantities that are conserved: energy (including mass), momentum, angular momentum (including spin), charge, electron-family number, muon-family number, and baryon-family number.
	has definition Law that identifies a quantity, such as energy, that remains unchanged throughout a transformation. All conservation laws are thought to involve symmetries.
	is a kind of law
conservation of angular momentum	has conserved quantity angular momentum
	has definition The principle that the angular momentum of a system (the momentum of rotation about a point) remains the same as long as no external torque acts.
	has definition The total angular momentum of an isolated dynamical system does not change during the course of its evolution.
	is a kind of conservation law
conservation of charge	has conserved quantity charge
	is a kind of conservation law
conservation of energy	has conserved quantity energy
	has definition The principle that the total energy of a closed system never changes, that energy is only converted from one form to another. This principle must be enlarged under special relativity to include mass-energy.
	has definition The total energy of a system (including kinetic energy and gravitational energy) is conserved and does not vary. Thus, kinetic energy can only increase at the expense of gravitational potential energy. Modern physics has modified the law of conservation of energy, since matter can be created or annihilated; a more general law is the conservation of mass and energy.
	is a kind of conservation law
conservation of mass and energy	has conserved quantity mass and energy
	has definition Important physical principle and one of the basic laws of physics stating that matter is neither created nor destroyed (although mass may become energy, the energy quantitatively represents the mass). One exception to this principle is a singularity; another follows from the theory of virtual particles.
	is a kind of conservation law
conservation of matter	has conserved quantity matter
	has definition The principle that matter is neither created nor destroyed. This principle is only approximately true, since special relativity shows that matter and energy are equivalent and interconvertible.
	is a kind of conservation law
conservation of momentum	has conserved quantity momentum
	has definition The principle that the linear momentum of a system (in Newtonian mechanics, mass times velocity) remains the same as long as no external force acts.
	is a kind of conservation law
conservative scattering	has definition Scattering that occurs in the absence of absorption.
	is a kind of scattering
consistent	has definition The property possessed by a scientific theory when it contains and extends an earlier well-supported theory; for example, general relativity is consistent with Newtonian gravity.
	is a kind of theory related concept
constant	is a kind of number
constellation	has boundary defined in equatorial coordinates
	has component asterism
	has definition Precisely defined area of the celestial sphere, associated with a grouping of stars, that the International Astronomical Union has designated as a constellation.
	has genitive which is used when referring to a star in the constellation
	has historical origin asterism with pictorial or mythical significance
	has purpose to divide the celestial sphere into small visually recognizable star classification regions
	is a kind of equatorial sky area
	is a part of celestial sphere
constellation formerly part of Argo Navis	has definition a constellation created by the international astronomical union by breaking up the constellation Argo Navis
	has historical origin part of the large constellation Argo Navis
	is a kind of constellation
constellation named by Bayer	has definition a constellation named by Johann Bayer the author of the Uranometria star atlas 1607
	is a kind of constellation
	is named by Johann Bayer
constellation named by de Lacaille	has definition a constellation named by Abbé Nicolas Louis de Lacaille
	is a kind of constellation
	is named by Abbé Nicolas Louis de Lacaille
contraction	has definition A mass motion towards the center of gravity of a celestial body
	is a kind of mass motion
convection	has definition A mass motion in a circulatory pattern. Process in the Sun (and possibly other stars) perhaps caused by solar rotation, which produces the immensely powerful electrical and magnetic fields associated with sunspots.
	is a kind of mass motion
convective zone	has definition Region in a stellar interior where convection dominates the heat flow
	is a part of solar interior
coordinate	has component coordinate component
	has definition Quantities that provide references for locations in space and time.
	is a kind of point
coordinate component	has definition A component of a coordinate system, components are usually an angle or a length
	is a component of coordinate
	is a kind of quantity
coordinate transformation	has definition Method of relating observations from one frame of reference to another.
	is a kind of transformation
Copenhagen interpretation	has competing theory Copenhagen interpretation
	has definition The view of quantum mechanics holding that prior to the measurement, a system has no physical existence and is describable only in terms of the probability of each possible result of a measurement. After a measurement the physical system exists in one and only one of its possible states.
	is an instance of quantum mechanics interpretation
Copernicus	has contribution the Copernican model of the solar system with the sun at its center
	is an instance of scientist
copper	has image
	has ocean oxidation state II
	has ocean residence time 3000 years
	is a kind of recycled oceanic element
	is a kind of transition metal
core-halo galaxy	has abundance 20% of the known extended radio sources
	has definition A class of radio source characterized by an emission "halo" surrounding a more intense "core". About 20% of the known extended radio sources are of the core-halo type.
	is a kind of radio galaxy
corona	has definition Outermost atmosphere of the Sun immediately above the chromosphere, consisting of hot (1-2 × 106 K), low-density (about 10-16 g cm-3) gas that extends for millions of miles from the Suns's surface. Ordinarily it can be seen only during a total solar eclipse. Its shape varies from almost spherical at sunspot maximum to unsymmetrical at minimum. Its high temperature is probably caused by MHD shock waves generated below the photosphere. The corona, together with solar flares, is the source of solar X-rays. It is the corona, not the photosphere, that is studied by radio astronomers, except at very short wavelengths.
	is a part of solar atmosphere
Corona Australis	has acronym CrA
	has boundary
	has genitive Coronae Austrinae
	has synonym Southern Crown
	is a part of celestial sphere
	is an instance of constellation
Corona Borealis	has acronym CrB
	has boundary
	has genitive Coronae Borealis
	has synonym Northern Crown
	is a part of celestial sphere
	is an instance of constellation
coronal green line	has definition An emission line of Fe XIV, the strongest line in the solar corona.
	has species Fe XIV
	has transition 2P3/2 - 2P1/2
	has wavelength 5303 Å
	is a kind of emission line
coronal hole	has definition An area where the extreme-ultraviolet and X-ray coronal emission is abnormally low or absent; a coronal region apparently associated with diverging magnetic fields. A great part, if not all, of the solar wind starts from coronal holes.
	is a part of corona
coronene	has definition The first ultraviolet phosphor to be tried on the surface of a CCD.
	is a kind of coating
corrector plate	has definition Thin lens-like optical piece which removes certain optical aberrations.
	is a kind of aspheric
Corvus	has acronym Crv
	has boundary
	has genitive Corvi
	has synonym Crow
	is a part of celestial sphere
	is an instance of constellation
Cosmic Background Explore	has acronym COBE
	has definition satellite that studies the microwave background.
	is an instance of NASA satellite
cosmic matter density	has definition The average number of fermions per unit volume of space throughout the universe. Since matter is depicted in general relativity as bending space, the value of the cosmic matter density, if known, could reveal the overall curvature of cosmic space. See critical density, omega.
	is a kind of density
cosmic rays	has composition 85% protons, 14% alpha-particles, 1% electrons, << 1% heavy nuclei
	has definition High-energy charged particles which stream at relativistic velocities down to Earth from space. The Sun ejects low-energy (107 - 1010 eV) cosmic rays during solar flares (those of lower energy than this are unobservable from Earth because of solar system magnetic fields). Those of intermediate energy (1010 - 1016 eV) have an isotropic distribution, and are apparently produced in the Galaxy. Possible sources of acceleration are shock waves accompanying supernovae (although cosmic rays have a higher hydrogen content than would be expected from a star that has processed material to iron), and the rotating magnetic fields of pulsars. The light elements Li, Be, and B have a higher abundance ratio in cosmic rays than in the solar system.
	has energy 2 GeV (average)
	has synonym corpuscular radiation
	is a kind of charged particle
	is a kind of radioactive particle
cosmic string	has definition Long, stringlike concentrations of matter-energy that may have formed during symmetry breaking in the first moments of the big bang. If they exist, they would be candidates for the seed perturbations of structure formation.
	has definition Microscopically thin, spaghetti-like objects which, according to some theories of elementary particles, could form randomly during a phase transition in the early universe. Cosmic strings could provide the seeds for structure formation in the universe, as an alternative to the possibility that the seeds originated as quantum fluctuations during inflation.
	has definition Some contemporary cosmological theories suggest that boundaries were formed between different regions of the universe at the moment of creation. These boundaries survive today as "cosmic strings", incredibly thin but very massive strings many light years in length.
	is a kind of cosmology theory
	is a kind of theoretical celestial body
cosmic year	has definition Time the Sun takes to "orbit" in galactic rotation: about 225 million years.
	has value 225 million years
	is an instance of time unit
cosmogony	has definition The study of the origin of celestial systems, especially the solar system.
	is a kind of cosmology
cosmological constant	has definition A constant introduced into Einstein's field equations of general relativity in order to provide a supplement to gravity. If positive (repulsive), it counteracts gravity, while if negative (attractive), it augments gravity. It can be interpreted physically as an energy density associated with space itself.
	has definition A contribution to gravity that results from the effective mass density, or energy density, in the vacuum. A positive cosmological constant acts as if it were negative gravity - it makes two masses repel each other instead of attract each other. Einstein's first cosmological model contained a cosmological constant, which appeared as an additional term in the equations of general relativity. (See false vacuum; vacuum.)
	has definition A parameter that determines the strength of the cosmological term in the equations of general relativity. This term was added by Einstein because he thought the universe was static, and the term provided a repulsive gravitational force that was needed to prevent the universe from collapsing under the force of ordinary gravity. The false vacuum of inflationary models creates a similar repulsive gravitational force, except that it prevails for only a brief period in the early universe. The cosmological constant is often assumed to be zero, but it might make a significant contribution to the evolution equations of our universe.
	has definition A possible third parameter in cosmology, in addition to the Hubble constant and omega (Ω). Most cosmologists believe the cosmological constant is zero, but if it is not, it would make the universe older than astronomers calculate from the Hubble constant and Ω. The size of the cosmological constant is designated by the Greek letter lambda (λ).
	has definition A term added by Einstein to the gravitational field equations of his theory of general relativity. Such a term would produce a repulsive antigravity force at very large distances and would correspond to energy locked up in the curvature of space-time itself. There is, at present, no evidence for the existence of a cosmological constant (although one may have existed in the past).
	has definition A term introduced by Einstein into his field equations of gravitation to permit a static model of the universe. It corresponded, as introduced originally, to a cosmic repulsion force that could withstand the attractive tendency of gravity.
	has definition A term sometimes employed in cosmology to express a force of "cosmic repulsion", such as the energy released by the false vacuum thought to power exponential expansion of the universe in the inflationary universe models. Whether any such thing as cosmic repulsion exists or ever played a role in cosmic history remains an open question.
	has definition Einstein's general theory of relativity allows for space-time curvature even in an empty universe. The amount of this curvature is given by the cosmological constant. Current indications are that this constant must be zero, but the reason for its vanishing remains a mystery.
	is an instance of astronomical constant
cosmological constant problem	has definition The puzzle of why the cosmological constant has a value which is either zero, or in any case roughly 120 orders of magnitude or more smaller than the value that particle theorists would expect. Particle theorists interpret the cosmological constant as a measure of the energy density of the vacuum, which they expect to be large because of the complexity of the vacuum. See vacuum.
	is an instance of problem
cosmological redshift	has anomaly A few galaxies show blueshifts, the most famous being Andromeda galaxy, but most show redshifts, due to the expansion of the universe.
	has definition The redshift due to the expansion of the Universe. Contrary to popular belief, this is not a Doppler shift. Most galaxies move away from us, but this is not the cause of their redshifts. Instead, as a light wave travels through the fabric of space, the universe expands and the light wave gets stretched and therefore redshifted.
	has discoverer Slipher
	has discovery date 1926
	has property wavelength shift is directly proportional to distance
	has symbol z
	has value the cosmological redshift as observed is the ratio of the radius of the Universe at the present epoch to the radius of the Universe at the time the radiation left the distant object.
	is a kind of wavelength shift
cosmology	has definition The study of the origin, structure, and evolution of the Universe on the largest possible scale. In present usage, it frequently includes cosmogony.
	is a kind of extragalactic astronomy
cosmology theory	has domain cosmology
	is a kind of astronomy theory
Coster-Kronig transition	has definition An Auger transition in which the vacancy is filled by an electron from a higher subshell of the same shell.
	is a kind of Auger transition
Cotton Candy nebula	has image
	has synonym IRAS 17150-3224
	is an instance of planetary nebula
coudé focus	has definition A focus used primarily for spectroscopy. In this arrangement light from the primary mirror is reflected along the polar axis to focus at a fixed place separate from the moving parts of the telescope, where large pieces of equipment can be fitted without interfering with the telescope's balance. (The word comes from a French word meaning "bent like an elbow", not from a man's name)
	has definition A stationary focal point in an equatorial mounted telescope obtained by an arrangement of small auxiliary mirrors in the converging beam which eventually directs the light down the hollow polar axle of the telescope.
	is a kind of focus
coulomb	has base unit s·A
	has definition The practical and the SI unit of charge. It is the quantity of electricity transported in one second by a current of one ampere. From 1908 to 1948 the international coulomb, derived from the international ampere, was in use. Like the other international units it was replaced by the absolute unit on 1 January 1948. The name coulomb was given to the unit at the first meeting of the IEC in Paris in 1881. At this meeting two of the five units which were given definitions were named after French scientists. These were the ampere (A. M. Ampère 1775-1836) and the coulomb (C. A. Coulomb 1736-1806). (1 international coulomb = 0.99985 absolute coulomb.)
	has definition Unit of charge.
	has equivalent 2.998 × 109 esu
	has symbol C
	is an instance of charge unit
	is an instance of named derived SI unit
	represents electric charge, quantity of electricity
Coulomb collision	has definition The collision between two charged particles.
	is a kind of collision
Coulomb's law	has definition The force between two charged particles varies directly as the size of the charges and inversely as the square of the distance between them.
	is an instance of electromagnetic law
CP violation	breaks CPT invariance
	has definition A reaction between subatomic particles is said to be a "CP violating" reaction if the reaction produces a different result when the electrical charges of the particles are changed to their opposites and the mirror image of the particle trajectories is used.
	is a kind of symmetry breaking
CPT invariance	has definition A symmetry which is believed to hold true for all particles throughout the course of universal history. It states that matter and antimatter would only react in the same way if the spins of the antimatter particles were reversed and the reaction was caused to run backwards in time.
	has definition A theory has "CPT invariance" if for every possible reaction between subatomic particles, a reaction can also occur in which the electrical charges of the particles changed to their opposites, the mirror image of the particle trajectories is used, and the directions of motion are reversed. Assuming general notions of modern physics, all conceivable theories of nature are CPT invariant.
	is a kind of symmetry
Crab Nebula	has age 947 years
	has definition A chaotic, expanding mass of gas in Taurus, the remnant of a Type I supernova whose light reached Earth in 1054. It is an intense radio source, and its visible light is strongly polarized. It is also a source of X-rays and gamma-rays. Its total mass is about 1 Msun, but the total energy radiated by the Crab is 1037-1038 ergs s-1. It is periodically occulted by the Moon, and every June its radio spectrum is occulted by the solar corona.
	has definition A supernova remnant.
	has distance 2 kpc
	has explosion date 1054 A.D.
	has image
	has Messier number 1
	has synonym 2U 0531+22
	has synonym M 1
	has synonym Taurus A
	is a part of Taurus
	is an instance of Messier object
	is an instance of supernova remnant
Crab pulsar	has definition A pulsar associated with the Crab Nebula. It has the shortest period of any known pulsar.
	has period 0.0331 seconds
	has synonym NP 0532
	is a part of Crab Nebula
	is a part of Milky Way
	is a part of Taurus
	is an instance of pulsar
Crater	has acronym Crt
	has boundary
	has genitive Crateris
	has synonym Cup
	is a part of celestial sphere
	is an instance of constellation
creationism	has definition Belief that the universe was created by God in the relatively recent past, as implied by literal interpretations of biblical chronology, and that the species of terrestrial life did not arise through Darwinian evolution but, rather, all came into existence at once.
	is a kind of religious belief
Crepe Ring	has definition Rather transparent inner ring of the saturn ring system.
	has definition The second innermost ring of Saturn, it has fewer particles and is less dense than the outer rings; therefore, it is harder to observe.
	has diameter 149300 km
	has discoverer Bond
	has discovery date 1850
	has synonym C ring
	has width 18000 to 20000 km
	is a kind of ring
	is a part of Saturn ring system
cretacious period	has duration 72 million years
	has start time 135 million years ago
	is a kind of mesozoic era
critical density	has definition If the cosmological constant is assumed to vanish, then the critical mass density is that density which puts the universe just on the border between eternal expansion (open universe) and eventual collapse (closed universe).
	has definition The cosmic density of matter required to "close" the universe and so, eventually to halt cosmic expansion. Its value amounts to about ten hydrogen atoms per cubic meter of space. The observed density is so close to the critical value that the question of whether the universe is open or closed has not yet been resolved by observation. See open universe, closed universe.
	has definition The density that just stops the expansion of space, after infinite cosmic time has elapsed. In the standard models, the critical density requires that the spatial geometry be flat.
	has definition The value of average cosmic mass density above which the universe is closed. The average mass density of the universe is obtained by measuring the mass in a very large volume of space, including many galaxies, and dividing by the size of the volume. The critical mass density is determined by the current rate of expansion of the universe. According to estimates of the current rate of expansion, the current critical mass density is about 10-29 grams per cubic centimeter. According to the best measurements, the average mass density of our universe appears to be about one tenth the critical mass density. (See closed universe; omega; open universe.)
	is a kind of density
critical equatorial velocity	has definition In rotating early-type stars, that velocity at which the ratio of centrifugal force to gravity at the equator is unity.
	is a kind of equatorial velocity
Cross-axis equatorial telescope	has mounting equatorial with cross-axis
	is a kind of equatorial telescope
crossing time	has definition The time it takes a particle to travel from one point in its orbit to another point 180° away.
	is an instance of time
crucial experiment	has definition An experiment that has the power to decide between two competing theories.
	is a kind of experiment
Crux	has acronym Cru
	has genitive Crucis
	has historical image
	has synonym Southern Cross
	is a part of celestial sphere
	is an instance of constellation
CS star	has definition Group characteristics are: strong bands of CN, outstandingly strong absorption near the Na D lines, usually sufficient structure in the 6400-6500 Å region to suggest ZrO.
	has definition Star exhibiting combined characteristics of C- and S-type stars - i.e. the presence of both C2 and ZrO bands.
	is a kind of carbon star
culmination	has definition Passage of a celestial object across the observer's meridian. More precisely, culmination is the passage through the point of greatest altitude in the diurnal path.
	has definition The instant at which a celestial object crosses the meridian.
	has period 1 day
	has synonym meridian passage
	is a kind of location dependent periodic celestial event
curie	has definition A unit of radioactivity which is now defined as the quantity of any radioactive nuclide undergoing 37.00 × 109 disintegrations per second. The unit was adopted at a Radiography Conference in Brussels in 1910 when it was defined as the radioactivity associated with the quantity of radon in equilibrium with one gram of radium. The present definition, which refers to a unit of the same size but described in terms independent of the disintegration of radon, was agreed at the Copenhagen meeting of the International Commission on Radiological Units in July 1953. The unit is named after Pierre Curie (1859-1906), one of the discoverers of radium. The curie is too large for normal laboratory work where the radioactivity is of the order of millicuries. The number of disintegrations occurring per second is called the activity of a sample and a unit for this was originally the reciprocal second but this has been superseded by the curie.
	has definition Unit of radioactivity.
	has equivalent 3.7 × 1010 becquerel
	is an instance of radioactivity unit
Curie temperature scale	has definition This is sometimes used for indicating temperature in the vicinity of absolute zero. It is based on Curie's law, which states that the susceptibility of a paramagnetic material is approximately proportional to its absolute temperature.
	has synonym magnetic temperature
	is an instance of temperature unit
curium	has image
	is a kind of transuranium element
current	has unit current unit
	is a kind of electromagnetic quantity
current density	has definition Amount of charge passing through a unit area per unit time.
	is a kind of electromagnetic quantity
current density unit	has definition ampere per square meter
	has symbol A·m-2
	is a kind of derived SI unit
current unit	is a kind of electromagnetic unit
	is a unit of current
Curtis	has birth date 1872
	has career 1893-1900 : Taught Latin & Greek, later math 1902-1920 : Lick 1920-1930 : Director, Allegheny 1931-1942 : Director, U. Michigan Observatories
	has death date January 9, 1942
	has degree 1893 : classics, U. Michigan 1902 : PhD. U. Virginia
	has name Heber Doust Curtis
	has orbituary 1942, PASP 54, 54.
	is an instance of 19th century scientist
	is an instance of astronomer
CV Serpentis	has definition A sometimes-eclipsing binary composed of a Wolf-Rayet star and a B0 star.
	has orbital period 29.6 days
	is a part of Serpens
	is an instance of eclipsing binary
	is an instance of Wolf-Rayet
cyan	is a kind of optical
cyanoacetylene	has symbol HC3N
	is an instance of interstellar molecule
cyanogen band	has definition Molecular absorption band found in the spectra of stars of type G0 and later.
	has species CN
	has use luminosity criterion; it is more pronounced in giants than in dwarfs of the same spectral type
	is a kind of interstellar band
	occurs in G0 star or later
cyanogen radical	has symbol CN
	is an instance of diatomic molecule
	is an instance of interstellar molecule
Cygnus	has acronym Cyg
	has boundary
	has genitive Cygni
	has synonym Northern Cross
	has synonym Swan
	is a part of celestial sphere
	is an instance of constellation
Cygnus A	has definition A double radio source, the third strongest radio source in the sky (after the Sun and Cas A), at one time believed to be caused by the collision of two galaxies. It has now been identified with a distant peculiar cD galaxy (z ≈ 0.056).
	has synonym 2U 1957+40
	has synonym 3C 405
	is an instance of double radio source
	is an instance of X-ray source
Cygnus Loop	has age 20000 years
	has definition A supernova remnant, consisting of a large loop of gas ejected from a star. It is 100 pc above the galactic plane. (X-ray observations give a distance of 2-3 kpc.) It is a thermal bremsstrahlung source of soft X-rays with a spectral temperature of 2 × 106 K.
	has distance 770 pc
	has image
	has synonym Cygnus X-5
	has synonym NG6 6992
	has synonym Veil Nebula
	is a part of Cygnus
	is an instance of supernova remnant
	is an instance of X-ray source
Cygnus X-1	has definition A black hole candidate in the constellation Cygnus and a source of X-rays.
	has definition An X-ray source. The visible component is the ninth-magnitude supergiant HDE 226868 (O9.7 Iab). It has rapid night-to-night variations in spectral features.
	has distance 2.5 kpc
	has eccentricity e ≈ 0.06
	has inclination i ≈ 27°
	has period 5.5998 days
	has primary mass 20 Msun
	has secondary mass > 6 Msun
	has synonym 3U 1956+35
	is a part of Cygnus
	is an instance of X-ray source
Cygnus X-2	has definition An X-ray source optically identified with an irregular variable star.
	has synonym 3U 2142+38
	is a part of Cygnus
	is an instance of X-ray source
Cygnus X-3	has definition An X-ray binary. It is also an infrared source, a cosmic ray source, and a strongly variable radio source (interstellar extinction is too high for visible light observations). It is best fitted by a model of an expanding cloud of relativistic electrons emitting synchrotron radiation around a neutron star.
	has discovery date 1966
	has distance 10 kpc
	has orbital period 4.8 hour
	has synonym 2U 2030+40
	is a part of Cygnus
	is an instance of binary star
	is an instance of X-ray source
Cyrillids	is an instance of meteor shower
D galaxy	has definition A supergiant radio galaxy (the most common type of radio galaxy) which has an elliptical nucleus surrounded by an extended envelope. Or, an optical galaxy with a very bright nucleus. In the Morgan classification, a galaxy with rotational symmetry but without pronounced spiral or elliptical structure (a dustless galaxy). In the Yerkes 1974 system a galaxy with an elliptical-like nucleus surrounded by an extensive envelope (see also R galaxy).
	is a kind of radio galaxy
D layer	has altitude > 100 km or higher
	has definition The lowest part of Earth's ionosphere.
	has radio reflectivity "broadcast" radio waves
	is a part of ionosphere
D line	has definition Spectral line of neutral sodium, also the strongest interstellar line.
	has species Na I
	is a kind of Fraunhofer line
	is a kind of interstellar line
	is a kind of interstellar line
D ring	has definition The innermost ring of Saturn.
	has discovery date 1969
	is a kind of ring
	is a part of Saturn ring system
d-electron	has definition An orbital electron whose l quantum number is 2.
	has orbital quantum number 2
	is a kind of bound electron
D1 line	has definition Spectral line of neutral sodium.
	has wavelength 5896 Å
	is a kind of D line
D2 line	has definition Spectral line of neutral sodium.
	has wavelength 5890 Å
	is a kind of D line
DA white dwarf	has definition only strong hydrogen lines present
	is a kind of white dwarf
dark cloud gravitational contraction	is a kind of gravitational contraction
dark flight	has definition phase in the flight of a meteor after the ratardation point when the meteoroid is no longer incandescent
	has duration from the point of intial contact with atmosphere until the retardation point
	has start time the point of intial contact with the atmosphere
	is a kind of meteor event
dark halo	has definition Massive, nonluminous matter of unknown kind that surrounds and envelope of a galaxy
	has definition The massive outer region of the Milky Way that surrounds the disk and stellar halo. The dark halo consists mostly of dark matter, whose form is unknown. Though it emits almost no light, the dark halo outweighs the rest of the Galaxy.
	has definition The unseen mass that is believed to surround each galaxy and whose gravitational effects are believed to hold the galaxy together.
	is a part of Milky Way
dark matter	has definition Any form of matter which exists in the Universe in a non-luminous form.
	has definition Material astronomers cannot see but whose presence they believe in either because they detect its gravitational influence or because certain theories predict its existence. For example, astronomers believe that the outer part of the Galaxy harbors dark matter, because they notice its gravitational influence on the stars they can see; and inflationary cosmologists believe that the universe is full of dark matter, because inflation predicts that the universe has a large density.
	has definition Matter in the universe that we detect by its gravitational influences, yet do not see. Dark matter that has small random speed and is easily concentrated by gravity is called cold dark matter. Dark matter that has large random speed and is thus able to resist gravitational clumping is called hot dark matter. Recent models to explain the observed pattern of galaxy clustering can be characterized, in part, as to whether they invoke hot dark matter or cold dark matter. However, since we do not know what the dark matter is, we do not have any direct evidence of whether it is cold or hot.
	has definition Matter that is detected only by its gravitational pull on visible matter. At least 90%, and possibly 99% of the matter in the universe is dark. The composition is unknown; it might consist of very low mass stars or supermassive black holes, but big-bang nucleosynthesis calculations limit the amount of such baryonic matter to a small fraction of the critical mass density. If the mass density is critical, as predicted by the simplest versions of inflation, then the bulk of the dark matter must be a gas of weakly interacting non-baryonic particles, sometimes called WIMPS (Weakly Interacting Massive Particles). Various extensions of the standard model of particle physics suggest specific candidates for the WIMPs.
	has definition Matter that is invisible to us because it emits little or no light. As much as 90%-99% of the mass of the universe may be dark.
	has definition Matter whose existence is inferred on the basis of dynamical studies - e.g., the orbits of stars, in galaxies - but which does not show up as bright objects such as stars and nebulae. Its composition is unknown: It might consist of subatomic particles, or of dim dwarf stars or black holes, or a combination of various sorts of objects.
	has definition Matter whose presence is inferred from dynamical measurements but which has no optical counterpart. The luminous regions of galaxies have mass-luminosity ratios of about 10. However, the mass-luminosity ratio in the outer halos of many spiral galaxies is 100 or more; one sees the brightness fall off with distance from the center of the galaxy but considerable mass is present. A similar situation prevails in galaxy clusters, where nonluminous matter must provide most of the self-gravitational attraction that holds the clusters together. The missing mass is not really missing; it is present but invisible (at least to current detectors). It is generally believed to consist either of the remnants of massive stars or of planetary-sized objects comparable in mass to Jupiter.
	has synonym hidden mass
	is a kind of hypothetical particle
	is a part of dark halo
dark nebula	has definition A relatively dense cloud of interstellar matter whose dust particles obscure the light from stars beyond it and give the cloud the appearance of a region devoid of stars.
	has density up to 104 particles per cm3
	is a kind of nebula
	is a part of dust
data collection	is a kind of abstraction
data standard	is a kind of abstraction
database	is a kind of data collection
day	has definition An interval of 86400.51 seconds, unless otherwise indicated.
	has symbol d
	has value 86400.51 seconds
	has value in SI unit 24 h = 86400 s
	is a kind of non SI unit
	is a kind of time unit
db galaxy	has definition One of a small number of dumbbell-shaped radio galaxies. They might be called D systems with double nuclei, in which two elliptical nuclei share a common extended envelope.
	is a kind of D galaxy
DB white dwarf	has definition only strong helium lines present
	is a kind of white dwarf
DC white dwarf	has definition continuous spectrum, no lines clearly visible
	is a kind of white dwarf
de Sitter model	has definition A geometrical model (1917) of an empty universe, based on Einstein's field equations.
	has definition A model of the universe that contains no matter but only a positive cosmological constant. It expands exponentially forever.
	has definition A particular solution to Einstein's cosmological equations, found by Wilhelm de Sitter in 1917, in which space expands at a rapid, exponential rate. This solution was very different from the solutions of Friedmann and of Lemaitre, in which the universe expands at a much slower rate (a rate with the distance between any two points increasing as something between the square root of time and linearly with time). The Friedmann and Lemaitre type solutions became incorporated in the standard big bang model. Recent modifications of the big bang model, such as the inflationary universe model, propose that the universe went through a period of exponential growth, or a de Sitter phase, early in its evolution.
	is a kind of cosmology theory
dead person	has death date
	has definition a person that has died
	has orbituary
	is a kind of person
decay process	is a kind of physical process
deceleration parameter	has definition A dimensionless quantity describing the rate at which the expansion of the Universe is slowing down because of self-gravitation: it gives a measure of the matter density. In Friedmann's equation (which describes many cosmological models) q0 = - 1 indicates a steady-state universe, q0 < +1/2 indicates an open universe, q0 = +1/2 indicates a flat Euclidean universe, and q0 > 1/2 indicates a universe that is decelerating and will eventually contract. Sandage and Tammann (1975) obtain q0 = 0.10 for H0 = 55 km s-1 Mpc-1.
	has definition A parameter (that denotes the rate of change with time of the Hubble constant.
	has definition A parameter that measures the rate of slowing down of the expansion of the universe. Gravity causes the slowing down. The deceleration parameter equals omega (another cosmological parameter) when the universe is dominated by radiation, approximately the first 100000 years after the big bang, and 1/2 omega when the universe is dominated by matter. Since the deceleration parameter is equivalent to omega (assuming a cosmological constant of zero, as often done), it determines the ultimate fate and spatial geometry of the universe. The deceleration parameter is often denoted by the symbol q0. (See omega.)
	has definition Quantity designating the rate at which the expansion of the universe is slowing down, owing to the braking effect of the galaxies' gravitational tug on one another. It is a function of the cosmic matter density.
	has symbol q0
	is an instance of astronomical constant
deci	has symbol d
	has value 10-1
	is an instance of unit prefix
declination	has definition Angular distance above (positive) or below (negative) the celestial equator. One of the co-ordinates, with right ascension, that defines the position of a heavenly body.
	has definition Angular distance north (+) or south (-) of the celestial equator to some object, measured in degrees, minutes, and seconds of arc along an hour circle passing through the object. Declination is analogous to latitude on the Earth's surface.
	has definition Angular distance on the celestial sphere north or south of the celestial equator. It is measured along the hour circle passing through the celestial object. Declination is usually given in combination with right ascension or hour angle.
	has definition Astronomical coordinate. Equivalent to latitude. The angle in degrees above or below the Celestial Equator, i.e. the projection onto the sky of the Earth's equator. Range of declination is from from zero to ± 90°.
	has definition Location on the sky in a north-south direction. Lines of declination are the celestial equivalent of latitude on Earth. Compare right ascension.
	has symbol δ
	is an instance of angle
	is an instance of equatorial coordinate component
deduction	has definition Process of reasoning in which a conclusion is derived from a given premise or premises, without a need for additional information. Compare induction.
	is a kind of reasoning process
DEep Near Infrared Survey	has acronym DENIS
	is an instance of sky survey
deformable mirror	has definition A very thin mirror whose shape can be changed by the force applied by many small pistons behind the mirror.
	is a kind of mirror
degeneracy pressure	has definition Pressure in a degenerate electron or neutron gas.
	has definition Pressure in a degenerate electron or neutron gas.
	is a kind of pressure
degenerate gas	has definition A gas of electrons (or, more generally, fermions) in which all the lowest quantum states are occupied. For such a gas, the pressure in the nonrelativistic limit is proportional to the 5/3 power of the density.
	has definition A state of matter found in white dwarfs and other extremely dense objects, in which strong deviations from classical laws of physics occur. As the density increases at a given temperature, the pressure rises more and more rapidly, until it becomes independent of temperature and dependent on density alone. At this point, the gas is said to be degenerate.
	has definition A state of matter found in white dwarfs and other ultrahigh-density objects, in which the electrons follow Fermi-Dirac statistics. According to the classical laws of physics, the pressure of a gas is proportional to the temperature and the density. However, in 1926 Fermi and Dirac showed that if the density were high enough, departures from classical laws would occur, in that if at a given temperature the density is increased, the pressure increases more and more rapidly until it becomes independent of the temperature and is a function of the density only. When this point is reached, the gas is said to be degenerate.
	has synonym Fermi gas
	is a kind of plasma
degree	has definition An angle subtended in the sky: From the zenith to the horizon is 90 degrees.
	is an instance of angle unit
degree (angle)	has symbol °
	has value in SI unit (π/180) rad
	is an instance of non SI unit
Deimos	has albedo 0.06
	has definition The outer satellite of Mars. Mariner 9 has shown that both Phobos and Deimos are locked in synchronous rotation with Mars.
	has discoverer A. Hall
	has discovery date 1897
	has eccentricity e = 0.003
	has inclination 1°.6
	has orbital period P = 1.26 days
	has radius 12 × 13 km
	is a part of Mars
	is an instance of natural satellite
deka	has symbol da
	has value 101
	is an instance of unit prefix
delay time	has definition Time lapse between the time a signal (e.g., a radar beam) is propagated out to a distant object and the time it is received after the object bounces it back.
	is an instance of time
Delphinus	has acronym Del
	has boundary
	has genitive Delphini
	has synonym Dolphin
	is a part of celestial sphere
	is an instance of constellation
delta	has definition Short-lived baryon.
	is an instance of hyperon
Delta Aquarid	has duration 8 days
	has radiant Delta Aquarii
	has rate 30 per hour
	has start time 29 July
	is an instance of meteor shower
Delta Capricorni	has B-V magnitude 0.29
	has declination -16 07 38
	has right ascension 21 47 02.3
	has spectral type Amv
	has synonym HR 8322
	has V magnitude 2.87
	is a part of Capricornus
	is an instance of A star
	is an instance of naked eye star
Delta Cephei	has definition A pulsating star in the constellation Cepheus. It was the second Cepheid discovered and lent its name to the entire class of stars.
	is a part of Cepheus
	is an instance of Population I Cepheid
Delta Crateris	has B-V magnitude 1.12
	has declination -14 46 43
	has right ascension 11 19 20.4
	has spectral type G8III-IV
	has synonym HR 4382
	has V magnitude 3.56
	is a part of Crater
	is an instance of G star
	is an instance of giant
	is an instance of naked eye star
Delta Del star	has definition A type of late A-type and early F-type star with very weak Ca II HK lines.
	is a kind of star
Delta Scuti	has B-V magnitude 0.35
	has declination -09 03 09
	has right ascension 18 42 16.3
	has spectral type F2IIIp<04>Del
	has synonym HR 7020
	has V magnitude 4.72
	is a part of Scutum
	is an instance of F star
	is an instance of giant
	is an instance of naked eye star
delta-ray	has definition A recoil electron ejected from an atom by an energetic charged particle. Delta-rays appear as branches in the main track of a cloud chamber.
	is a kind of free electron
Demeter	has definition Unofficial name for Jupiter X.
	has discoverer Nicholson
	has discovery date 1938
	has eccentricity e = 0.12
	has inclination i = 29°
	has orbital period P = 259.2 days
	is a part of Jupiter
	is an instance of natural satellite
Deneb	has B-V magnitude 0.09
	has declination +45 16 49
	has definition An A2 Ia supergiant at the head of the Northern Cross. Most distant first-magnitude star.
	has distance 430 pc
	has right ascension 20 41 25.8
	has spectral type A2Iae
	has synonym alpha Cyg
	has synonym HR 7924
	has V magnitude 1.25
	is a part of Cygnus
	is an instance of naked eye star
	is an instance of white supergiant
density	has definition An object's mass divided by its volume. Cotton has a low density; lead has a high density. Red giants have a low density; white dwarfs have a high density.
	has definition The amount per unit volume
	has definition The mean density of a celestial body is generally reckoned as its mass divided by its volume, expressed either in comparison with the density of water, in kilograms per cubic meter, or in relation to some other known density. The mean density of the Earth is thus 5.5 times that of water, i.e. 5.5 × 103 kg m-3 and is just less than four times that of the Sun. Yet the mean density of rocks at the surface is about half the overall mean value, and that of the Earth's central core is perhaps 2 1/2 times the overall value.
	is a kind of quantity
density wave theory	has author Lindblad (1925)
	has definition Spiral structure is modelled as a small-amplitude wave propagating with fixed angular velocity, as the compression wave goes through, it triggers star formation on the leading edge of the spiral arms.
	has implication the density waves rotate more slowly than the galaxy's stars and gas
	is a kind of galaxy theory
derived SI unit	has base unit defined in terms of the seven SI base units via a system of quantity equations
	has unit defined in terms of derived SI unit via a system of quantity equations
	is a kind of SI unit
descending node	has definition The point in the orbit of a solar-system body where the body crosses the ecliptic from north to south.
	is an instance of Sun orbital event
DESI	has definition The German national laboratory for high-energy physics, located near Hamburg. It is the home of the e+e- storage rings DORIS and PETRA, and the electron-proton machine, HERA.
	has location Hamburg, Germany
	is an instance of high energy physics institution
detached binary	has definition Binary star which is not in contact and in which no significant mass exchange is occurring.
	is a kind of binary star
detector	is a kind of optical device
determinism	has definition The doctrine that all events are the predictable effects of prior causes.
	is a kind of doctrine
deuterium	has atomic mass 2
	has crystal cell dimension a = 338, c = 560 pm for tetragonal
	has crystal cell dimension a = 360.0, c = 585.8 pm for h.c.p.
	has crystal cell dimension a = 509.2 pm for cubic
	has crystal type cubic for cubic
	has crystal type h.c.p. for h.c.p.
	has crystal type tetragonal for tetragonal
	has definition A rare heavy isotope of hydrogen. Believed to be the first compound nucleus formed in the infant universe. It was discovered in interstellar space in 1965. Because deuterium is quickly destroyed in nuclear reactions, one view is that most of the deuterium in the universe is primordial.
	has interstellar space D H ratio 1.4 × 10-5
	has magnetogyric ratio 4.1064 × 107 rad T-1 s-1
	has natural abundance 0.015 %
	has NMR frequency 15.351 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 8.2 × 10-313C = 1.00
	has nuclear magnetic moment μ = 0.8574376
	has nuclear quadrupole moment 2.860 × 10-31 m2
	has nuclear spin I = 1
	has number of neutrons 1
	has number of nucleons 2
	has oceanic D H ratio 1.6 × 10-4
	has relative NMR sensitivity 9.65 × 10-3 where 1H = 1.00
	has solar D H ratio < 10-6
	has space group Fm3m for cubic
	has space group I4 for tetragonal
	has space group P63/mmc for h.c.p.
	has symbol 2H
	has symbol D
	has synonym hydrogen 2
	has synonym hydrogen 2
	has uses Nuclear Magnetic Resonance, water containing deuterium instead of ordinary hydrogen is used as a moderator in nuclear reactors
	is an instance of hydrogen
deuteron	has charge 1
	has definition The nucleus of a deuterium atom. md = 2.01355 amu.
	has definition The nucleus of deuterium, an isotope of hydrogen. It consists of one proton and one neutron bound together.
	has symbol d
	is an instance of charged particle
	is an instance of nucleus
deuteron magnetic moment	applies to particle deuteron
	has symbol μd
	has uncertainty 0.000000018 × 10-26 J T-1
	has value 0.433073457 × 10-26 J T-1
	is an instance of particle magnetic moment
deuteron mass	applies to particle deuteron
	has symbol md
	has uncertainty 0.00000026 × 10-27 kg
	has value 3.34358309 × 10-27 kg
	is an instance of particle mass
device	has definition an instrumentality invented for a particular purpose
	is a kind of artifact
devonian period	has duration 60 million years
	has start time 405 million years ago
	is a kind of paleozoic era
diatomic molecule	has decompostion temperature < 10000 K
	has definition a molecule containing only two atoms which can be of different elements
	is a kind of molecule
dielectronic recombination	has inverse process autoionization
	is a kind of recombination
differential rotation	has definition As an object rotates, different parts of it may move at different rates. The Galaxy rotates differentially.
	has definition Of a stellar cluster or galaxy, the "orbiting" of stars nearer the center faster than those at the edge. Of a single body (such as the Sun or a gaseous planet), the axial rotation of equatorial latitudes faster than polar latitudes.
	is a kind of rotation
diffraction	has definition A property which distinguishes wave-like motions. When a wave is incident upon a barrier which is broken by a narrow slit (of comparable size to the wavelength), then the slit will act as a new isotopic source of secondary waves.
	has definition A wave-like property of light which allows it to curl around obstacles whose size is about that of the wavelength of the light. The disturbed waves then interfere to produce ripple-patterns.
	has definition The bending of light in passing a sharp edge or tiny aperture.
	is a kind of radiation direction modification
diffraction grating	has definition A system of parallel slits, where the slit width is of the same order as the wavelength of the incident radiation, which is capable of dispersing light into its spectrum.
	has definition An optical device containing thousands of very fine parallel grooves which produce interference patterns in a way which separates out all the components of the light into a spectrum.
	has definition Polished metallic surface (usually a metallic mirror on a block of glass or quartz) on which has been ruled a great number (in thousands) of parallel lines, used to split light to produce a spectrum.
	is a kind of spectrograph dispersing element
diffraction grating spectrograph	is a kind of spectrograph
dimethyl ether	has symbol (CH3)2O
	is an instance of interstellar molecule
Dione	has definition Fifth satellite of Saturn
	has discoverer Cassini
	has discovery date 1684
	has orbital period P = 4.5 days
	has radius 440 km
	is a part of Saturn
	is an instance of natural satellite
direct motion	has definition For orbital motion in the solar system, motion that is counterclockwise in the orbit as seen from the north pole of the ecliptic; for an object observed on the celestial sphere, motion that is from west to east, resulting from the relative motion of the object and the Earth.
	has definition Motion of a solar-system body from west to east across the sky.
	is a kind of motion
disk	has definition The central plane of a spiral galaxy, as distinguished from the halo or the nucleus.
	has definition The plate-shaped component of a spiral galaxy, in which the spiral arms are found.
	is a part of Milky Way
dispersion	has definition Resolution of white light into its component wavelengths, either by refraction or by diffraction.
	has definition The separation of a beam of light into the individual wavelengths of which it is composed by means of refraction or diffraction.
	is a kind of radiation direction modification
dissociative recombination	has definition Capture of an electron by a positive molecular ion, wherein part of the recombination energy dissociates the molecule into two neutral atoms.
	is a kind of recombination
distance	has definition The distance to a celestial object measured from the center of the Earth or Sun, in units of parsec or lightyear
	is an instance of equatorial coordinate component
	is an instance of length
diurnal motion	has definition The apparent daily motion of celestial bodies across the sky from east to west, caused by the Earth's rotation.
	has definition The apparent westward motion of celestial bodies, as seen from Earth, due to the Earth's axial rotation.
	is a kind of motion
dKe star	has definition K dwarf with hydrogen emission lines.
	is a kind of K star
	is a kind of UV Ceti star
dMe star	has definition M dwarf with hydrogen emission lines.
	is a kind of M star
	is a kind of UV Ceti star
DMSP satellite	is a kind of military spacecraft
DNA replication	is a kind of biochemical process
DO white dwarf	has definition both He and H lines present
	is a kind of white dwarf
doctrine	is a kind of belief
Doppler broadening	has cause thermal, turbulent, or mass motions of atoms along the line of sight
	has definition Line broadening caused by the thermal, turbulent, or mass motions of atoms along the line of sight.
	has effect small displacements of radiation absorbed or emitted by atoms toward longer and shorter wavelengths result in broadening of the lines
	is a kind of line broadening
Doppler shift	has definition Change in the apparent wavelength of radiation (e.g., light or sound) emitted by a moving body. A star moving away from the observer will appear to be radiating light at a lower frequency than if at rest; consequently, lines in the star's spectrum will be shifted toward the red (lower frequency) end of the spectrum. The existence of a direct relationship between the redshift of light from galaxies and their distances is the fundamental evidence for the expansion of the universe.
	has definition Displacement of spectral lines in the radiation received from a source due to its relative motion along the line of sight. A motion of approach results in a blueshift; a motion of recession results in a redshift.
	has definition Displacement of spectral lines in the radiation received from a source due to its relative motion in the line of sight. Sources approaching (-) the observer are shifted toward the blue; those receding (+), toward the red. The Doppler shift makes it possible to determine the radial velocity and the rotation of stars.
	has definition Effect on the wavelengths of light (or sound) emitted by a source at a distance that is increasing or decreasing in relation to the observer. If the distance is increasing, the wavelengths are "stretched" (the light received shifts towards the red end of the spectrum; sound received goes down in pitch). If the distance is increasing, the wavelengths are "squeezed" (the light received shifts towards the blue end of the spectrum; sound received goes up in pitch).
	has definition The alteration in frequency of electromagnetic radiation due to relative motion between the source and observer.
	has definition The alteration in frequency of electromagnetic radiation due to relative motion between the source and observer.
	has definition The apparent change of frequency or wavelength of radiation from an object due to its motion toward or away from us. If the object is receding the frequency is decreased and the wavelength is increased, i.e. becomes red-shifted.
	has definition The blueshift or redshift produced by an object's motion toward or away from us. If a star moves toward us, its light waves get compressed and its spectrum is blueshifted; if a star moves away from us, its light waves get stretched and its spectrum is redshifted. The Doppler shift allows astronomers to measure the radial velocities of stars. The Doppler shift is not responsible for the redshifts that most galaxies exhibit; that is a cosmological redshift.
	has definition The change in frequency of a wave (light, sound, etc.) due to the relative motion of source and receiver.
	has definition The shift in the received frequency and wavelength of a sound wave or electromagnetic wave that occurs when either the source or the observer are in motion. Approach causes a shift toward shorter wavelengths and higher frequencies, called a blueshift. Recession has the opposite effect, called a redshift.
	has value the amount of shift is directly proportional to relative velocity
	is a kind of wavelength shift
Dorado	has acronym Dor
	has genitive Doradus
	has historical image
	has synonym Goldfish
	has synonym mahi-mahi (a Hawaiian fish)
	has synonym Swordfish
	is a part of celestial sphere
	is an instance of constellation named by Bayer
double line spectroscopic binary	has definition a spectroscopic binary in which periodic Doppler shift is detected in both components of the binary star each out of phase by 180 degrees
	is a kind of spectroscopic binary
	can be used as a distance measuring technique
double radio source	has definition A radio galaxy, the bulk of whose radio emission comes from two sources on opposite sides of the visual galaxy. The radiation is presumably the result of an explosion in the nucleus of the parent galaxy, which caused the ejection at high speed of energetic particles in two opposite directions. About one-third of all known radio galaxies are double sources.
	is a kind of radio galaxy
double star	has definition A "system" of two stars that appear - because of coincidental alignment when viewed from Earth - to be close together; it is, however, an optical effect only, and therefore not the same as a binary star system (although until the twentieth century there were few means of distinguishing double and binary stars).
	is a kind of star
doublet	has definition In a spectrum, a pair of associated lines arising from transitions having a common lower energy level.
	is a kind of multiplet
down	has charge -1/3
	has definition A flavor of quark.
	is an instance of light quark
DQ Herculis	has definition A slow nova which also happens to be an eclipsing binary. It also has a regular flickering period of 71 seconds, the shortest period of regular variations known, except for pulsars and compact X-ray objects. It is probably composed of an M dwarf and a white dwarf with an accretion disk.
	has erruption date 1934
	has orbital period 4h39m
	has primary star white dwarf
	has secondary star M dwarf
	has synonym Nova Herculis 1934
	is an instance of eclipsing binary
	is an instance of slow nova
DQ white dwarf	has definition carbon lines (atomic or molecular) present.
	is a kind of white dwarf
Draco	has acronym Dra
	has boundary
	has genitive Draconis
	has synonym Dragon
	is a part of celestial sphere
	is an instance of constellation
Draco galaxy	has definition A dwarf elliptical galaxy, the intrinsically faintest (Mv = - 8.5) member of the Local Group (next to And I-III).
	has diameter 1 kpc
	has distance 80 kpc
	has distance from galaxy center 250000 light-years
	is a part of Draco
	is a part of Local Group
	is an instance of dwarf elliptical satellite galaxy
	orbits Milky Way
Draconids	is an instance of meteor shower
dubnium	is a kind of transactinide
DUMAND	is an acronym for Deep Underwater Muon and Neutrino Detector.
	is an instance of neutrino telescope
Dumbbell Nebula	has definition A planetary nebula of large apparent diameter and low surface brightness.
	has distance 220 pc
	has Messier number 27
	has synonym M 27
	has synonym NGC 6853
	is a part of Vulpecula
	is an instance of Messier object
	is an instance of planetary nebula
dust	has definition The dust component of a galaxy, includes dark cloud
	is a part of disk
dust tail	has charge little or none
	has definition Curved part of comet tail composed of dust driven by radiation pressure
	has synonym type II comet tail
	is a part of comet tail
dwarf	has definition Star that is on the main sequence - that is, a star fusing hydrogen into helium at its core.
	has definition Star with mass equal to or less than that of the sun. More generally, any star on or below the main sequence in the Hertzprung-Russell diagram.
	has definition Star, like the Sun, that fuses hydrogen into helium at its core. Ninety percent of all stars are main-sequence stars; examples are Sirius, Vega, Altair, and Alpha Centauri A, B, and C.
	has luminosity class V
	has symbol d
	has synonym main sequence star
	is a kind of star
dwarf Cepheid	has definition A group of pulsating variable stars with small variations in amplitude. They lie in the lower part of the Cepheid instability strip.
	has definition Type I Cepheids ( <Mv> +4 to +2).
	has period 1 to 3 hours
	has spectral type A star to F star
	has synonym delta Scuti star
	has synonym ultrashort-period Cepheid
	is a kind of Cepheid
	is a kind of Delta Del star
dwarf elliptical galaxy	has mass > 107 Msun (among the least massive galaxies)
	is a kind of elliptical galaxy
dwarf elliptical satellite galaxy	is a kind of satellite galaxy
dwarf galaxy	has definition A galaxy with low luminosity.
	has definition A small, faint galaxy, exemplified by those that orbit the Milky Way: Ursa Minor, Draco, Sculptor, Sextans, Carina, Fornax, Leo II, and Leo I.
	is a kind of galaxy
dwarf nova	has definition A short-period binary system consisting of a hot white dwarf (or a hot blue sdBe subdwarf) and a much cooler and slightly more massive late-type main-sequence companion which fills its Roche lobe and is ejecting mass onto the white dwarf through its inner Lagrangian point. (The light from dwarf novae comes from four sources: a white dwarf, a cool main-sequence star, a hot spot, and a disk.) The outbursts are usually assumed to be caused by the explosive nuclear burning of hydrogen-rich material accreted onto the surface of a degenerate star.
	has definition Cataclysmic variable in which the brightness increases suddenly at intervals ranging from several days to years.
	is a kind of nova
dynamical equinox	has definition The ascending node of the Earth's mean orbit on the Earth's equator; i.e., the intersection of the ecliptic with the celestial equator at which the Sun's declination is changing from south to north.
	is an instance of ascending node
	see also catalog equinox
	see also equinox
dynamical parallax	has definition The "parallax" (i.e., distance) for a binary star whose orbit is well known, derived by using the mass-luminosity relation and Newton's generalization of Kepler's third law.
	is a kind of parallax
dynamics	has definition Study, in physics, of the motion and equilibrium of systems under the influence of force.
	has definition The physics that explains how particles and systems move under the influence of forces. The dynamical laws of a theory give a quantitative statement of the response of a particle to an applied force.
	is a kind of physics
dyne	has definition A unit of force equal to the force necessary to give an acceleration of 1 cm sec-2 to a mass of 1 gram. 1 dyne of force is roughly equivalent to 1 mg of weight.
	has definition The force necessary to cause a mass of one gram to accelerate at one centimeter per second per second.
	is an instance of CGS unit
	is an instance of force unit
dysprosium	has image
	has ocean oxidation state III
	has ocean residence time 300 years
	is a kind of rare Earth
	is a kind of recycled oceanic element
DZ white dwarf	has definition no He nor H lines, but metallic lines present
	is a kind of white dwarf
E layer	has altitude 150 km
	has definition Former name for the D and E layers (q.v.).
	has definition The part of Earth's ionosphere where the temperature gradient reverses and starts to rise.
	has radio reflectivity "short-wave" radio waves
	has synonym Kennelly-Heaviside layer
	is a part of ionosphere
E line	has definition Spectral line consisting of a blend of Fe I and Ca I.
	has species Fe I and Ca I
	has wavelength 5270 Å
	is a kind of Fraunhofer line
E ring	is a kind of ring
	is a part of Saturn ring system
e-process	has definition A hypothetical group of nuclear reactions by which the iron group is assumed to be synthesized. At temperatures > 5 × 109 K and densities > 3 × 106 g cm-3 there are great numbers of collisions between high-energy photons and nuclei. These collisions break up the nuclei, the fragments of which promptly combine with other particles. Thus, there is in effect an equilibrium between formation and breakup. Since the iron group has the largest binding energies, the particles over the long run will tend to be trapped in these nuclei. The e-process (the e stands for equilibrium) is presumed to occur in a supernova explosion.
	is a kind of nucleosynthetic reaction
Eagle Nebula	has distance 7000 light years
	has image
	has synonym IC 4703
	is a part of Serpens
	is an instance of gaseous nebula
early star	has definition Hot star of spectral types O, B, A, and early F.
	has spectral type O, B, A, and early F
	is a kind of star
Earth	has age 4.6 ± 0.1 × 109 years
	has albedo 0.39 (water and land about 0.2; snow and clouds about 0.8)
	has aphelion distance 152100000 km
	has atmosphere composition 78% N2; 20.9% O2; 0.9% Ar, 0.03% C02 (by volume)
	has atmosphere density 1.3 × 10-3 g cm-3 (at sea level)
	has atmospheric pressure 1.013 × 106 dyn cm-2 (at sea level)
	has core density 10 g cm-3
	has core temperature 6400 K
	has definition Third planet from the Sun. First forms of life appeared about 3.2 to 3.5 × 109 years ago (Homo sapiens appeared as a species about 105 years ago).
	has eccentricity e = 0.0167
	has ecliptic inclination i = 0
	has effective temperature 287 K
	has equatorial radius 6378.17 km
	has escape velocity Vesc = 11.19 km s-1
	has magnetic field at surface 0.5 gauss
	has magnetic field in core 100 gauss
	has mass 5.977 × 1027 g
	has mean density 5.517 g cm-3
	has mean distance from Sun 149598500 km
	has obliquity 23°26'34" (in 1973)
	has orbital period 365.2564 days
	has orbital velocity vorb = 29.78 km s-1
	has perihelion distance 147100000 km in early January
	has polar radius 6356.9 km
	has precession 50'.256 per year
	has relativistic advance of perihelion 4'.6 per century
	has rotation period 23 hours 56 minutes 4.1 seconds
	has surface gravity 980 cm s-2
	is a part of our solar system
	is an instance of naked eye planet
	is an instance of terrestrial planet
Earth based telescope	has altitude height above sea level in meters
	has definition A telescope located on the surface of the Earth.
	has latitude in degrees, minutes, seconds (N or S)
	has longitude in degrees, minutes, seconds (E or W)
	has mounting designed to operate within a 1 g gravitational field
	has mounting manufacturer the person, company or institution that constructed the mounting
	has temperature ambient
	is a kind of electromagnetic telescope
Earth orbital event	has participants satellite, Earth
	is a kind of orbital event
Earth's lithosphere	is a part of Earth
Earth-crossing asteroid	is a kind of asteroid
	is a part of asteroid belt
east point	has azimuth 90
	has definition The point on the celestial horizon 90° clockwise from the north point. At the equinoxes the Sun rises in the east point.
	has elevation 0
	is an instance of local coordinate
EBS	has definition Electron Bombarded Silicon.
	is a kind of detector
eccentricity	has definition A measure of how round or elliptical an orbit is. A perfect circle has an eccentricity of 0 percent, and an extremely elliptical orbit has an eccentricity of just under 100 percent. The Sun has an orbital eccentricity of 6 percent, which means that at perigalacticon the Sun is 6 percent closer to the Galactic center than its mean distance and at apogalacticon the Sun is 6 percent farther from the Galactic center than its mean distance.
	has definition A parameter that specifies the shape of a conic section; one of the standard elements used to describe an elliptic orbit. (See elements, orbital.)
	has definition An orbital element representing the eccentricity of the elliptical orbit
	has definition In astronomy, the extent to which an elliptical orbit departs from a circular one. It is usually expressed as a decimal fraction, regarding a circle as having an eccentricity of 0.
	has definition The amount by which the elliptical orbit deviates from circularity: e = c/a, where c is the distance from the center to a focus and a is the semimajor axis.
	has symbol e
	is an instance of orbital element
eccentrics	has definition In Ptolemaic cosmology, displacement of the center of a rotating celestial sphere from the center of the universe.
	is a kind of outdated belief
echelle	has definition A type of diffraction grating with groove angles of 90°. With the grating at an angle of 45° the grooves resemble a staircase.
	is a kind of diffraction grating
eclipse	has definition Obscuration of one astronomical object (such as the sun) by another such object (such as the moon).
	has definition Occultation of one celestial body by another which passes between it and the observer. The solar eclipse is caused by the passing of the Moon between the Sun and the Earth in this way; such an eclipse may be complete (total) or incomplete (partial). Eclipsing binary stars also accord with this pattern. Alternatively - and exceptionally - a lunar eclipse is caused by the passage of the Earth between the Sun and the Moon, so that the Earth's shadow falls across the Moon, again either totally or partially, depending upon the position of the observer.
	has definition The obscuration of a celestial body caused by its passage through the shadow cast by another body.
	has definition The total or partial obscuration of the light from a celestial body caused by its passage into the shadow of another body (cf. occultation).
	is a kind of occultation
eclipse year	has definition The interval of time between two successive passages of the Sun through the same node of the Moon's orbit.
	has value 346.62 days
	is an instance of year
eclipsing binary	has definition A binary star of which, from the viewpoint of Earth, one of the two bodies regularly passes in front of the other. The resulting variation is perceived luminosity of some eclipsing binaries has led to their classification as variable stars.
	has definition A double star in which at least one of the two stars passes in front of and/or behind the other so that the system's total light periodically fades.
	has definition Eclipsing variables whose orbital plane lies so nearly in the line of sight that eclipses, as seen from the Earth, can occur and can be detected from their light curves.
	has eclipse duration
	is a kind of close binary
	is a kind of periodic variable
ecliptic	has definition Apparent linear path through the 12 constellations of the zodiac that the Sun seems to take during one Earth year, also representing therefore the "edge" of the plane of Earth's orbit. Because the equator of the Earth is at an angle of more than 22° to the plane of its orbit, the ecliptic is at the identical angle to the celestial equator, intersecting it at two points: the vernal and autumnal equinoxes.
	has definition Plane of the Earth's orbit. (Strictly speaking, the ecliptic is a mathematical fiction corresponding not to the actual plane of the Earth's orbit, but to one with all minor irregularities smoothed out.)
	has definition The mean plane of the Earth's orbit around the Sun.
	is a kind of plane
ecliptic coordinate	has celestial latitude
	has celestial longitude
	has component ecliptic coordinate component
	has definition A system of coordinates based on the plane defined by Earth's orbit around the Sun, which is inclined to the celestial equator.
	is a kind of coordinate
ecliptic coordinate component	is a component of ecliptic coordinate
	is a kind of coordinate component
Eddington approximation	has definition An approximation used in the study of radiative transfer. It is the assumption that the ratio of the second moment of the radiation field to the mean intensity is everywhere equal to 1/3, the value of this ratio for an isotropic field.
	is a kind of stellar theory
Eddington limit	has definition In essence, radiation pressure must not exceed gravity. It is the limit beyond which the radiation force on matter in the emitting region is greater than the gravitational forces that hold the star together. LE = 4πcGM/Ks, where Ks = Thomson and/or Compton scattering opacity. Eddington limit for a 1 Msun star, 1038 ergs s-1.
	is an instance of mass
Eddington's standard model	has definition A stellar model in which energy is transported by radiation throughout the whole star and the ratio of the radiation pressure to the gas pressure is assumed to be constant.
	is a kind of stellar theory
Eddington-Lemaitre universe	has definition A cosmological model in which the cosmological constant plays a crucial role by allowing an initial phase that is identical to the Einstein static universe. After an arbitrarily long time, the universe begins to expand. The difficulty with this model is that the initiation of galaxy formation may actually cause a collapse rather than initiate an expansion of the universe.
	is a kind of cosmology theory
effective temperature	has definition The temperature that a blackbody would have which emitted the same amount of energy per unit area as the star does: it is a temperature characteristic of the surface region. Teff of Sun, 5800 K.
	has symbol Teff
	is a kind of temperature
Egg Nebula	has distance 3000 light years
	has expansion rate 20 km/s
	has image
	has synonym CRL 2688
	is an instance of planetary nebula
EHF band	has frequency 30 to 300 GHz
	has wavelength 1 mm to 1 cm
	is a kind of microwave
Einstein	is an instance of grazing-incidence telescope
einsteinium	is a kind of transuranium element
elastic collision	has definition A collision between two particles which conserves the total kinetic energy and momentum of the system. For atomic collisions it is one involving energy less than the excitation potential of the atom.
	has definition Particle reactions in which the same particles emerge from the reaction as entered it (e.g. π- p → π- p). In inelastic scattering, where different and/or new particles emerge, energy is used to create new particles.
	is a kind of collision
electric constant	has symbol ε0
	has uncertainty 0
	has value 8.854187817 × 10-12 F m-1
	is an instance of universal constant
electric potential	has unit electric potential unit
	is a kind of electromagnetic quantity
electric potential unit	is a kind of electromagnetic unit
electrodynamics	has definition Study of the behavior of electromagnetic force in motion.
	is a kind of dynamics
electromagnetic constant	is a kind of fundamental physical constant
electromagnetic gauge symmetry	has definition Gauge symmetry underlying quantum electrodynamics.
	is a kind of gauge symmetry
electromagnetic law	has domain electromagnetism
	is a kind of law
electromagnetic quantity	is a kind of quantity
	is a kind of quantity
electromagnetic telescope	has definition telescope designed to collect and record electromagnetic radiation
	is a kind of telescope
electromagnetic unit	is a kind of unit
electromagnetism	has carrier boson photon
	has definition Force field of the electromagnetic force, consisting of electric and magnetic lines of force at each point in space.
	has definition Fundamental force of nature that acts on all electrically charged particles. Classical electromagnetics is based on Maxwell's and Faraday's equations, quantum electromagnetics on the theory of quantum electrodynamics (QED).
	has definition One of the four fundamental forces of nature, governing the electric and magnetic interaction between particles.
	has definition One of the four fundamental forces of nature. Electricity and magnetism arise from the electromagnetic force. The other three fundamental forces are the gravitational force, the weak nuclear force, and the strong nuclear force.
	has definition The force between charged particles, which accounts for electricity and magnetism. One of the four fundamental forces of nature, it is carried by photons and is responsible for all observed macroscopic forces, except for gravity.
	has definition The phenomena associated with electrical and magnetic forces. Electrical and magnetic forces are intimately related, since a changing electric field produces a magnetic field, and vice versa. Electromagnetic waves are an example of electromagnetism.
	has range infinite
	has strength 1 (relative to electromagnetism)
	is a kind of fundamental force
electron	has antiparticle positron
	has charge -1
	has definition A lepton with an electric charge of -1. An electron is also a fermion because it has a spin of one half.
	has definition A negatively charged spin-1/2 particle, which interacts via the electromagnetic, weak and gravitational forces. It has a mass of 0.511 MeV / c2, some 1800 times lighter than the proton.
	has definition A small, negatively charged particle that appears in every neutral atom, surrounding the positively charged nucleus like bees around honey.
	has definition A stable, negatively charged elementary particle - the lightest massive particle known. The classical electron radius is 2.82 × 10-13 cm; me = 9.1 × 10-28 g = 5.48597 × 10-4 amu. The electron family (see lepton) includes the electron e-, the positron e+, the electron neutrino νe, and the electron antineutrino νebar. Rest-mass energy of electron 8.186 × 10-7 ergs. Electron charge = 1.60219 × 10-19 coulombs.
	has definition Light elementary particle with a negative electrical charge. Electrons are found in shells surrounding the nuclei of atoms; their interactions with the electrons of neighboring atoms create the chemical bonds that link atoms together as molecules.
	has definition Negatively charged fundamental particle (also called a beta particle) found in the atoms of all elements, where it "orbits" (at different energy levels and with different directions of spin) round the central nucleus. The combined charge of the orbiting electrons is balanced (in a neutral atom) by the charge of an equal number of positively charged protons in the atomic nucleus. An electron is also the fundamental unit of electricity.
	is a kind of charged particle
	is a kind of lepton
	is a part of element
electron bombarded charge-coupled device	has acronym EBCCD
	has definition An imaging device containing a thin target material which emits electrons by the photoelectric effect when illuminated and then magnetically focuses these electrons to impact onto a silicon CCD where they generate a large charge.
	is a kind of charge-coupled device
electron Compton wavelength	applies to particle electron
	has equation
	has symbol λC
	has uncertainty 0.000000018 × 10-12 m
	has value 2.426310215 × 10-12 m
	is an instance of particle Compton wavelength
electron g factor	applies to particle electron
	has equation
	has symbol ge
	has uncertainty 0.0000000000082
	has value -2.0023193043737
	is an instance of particle g factor
electron gyromagnetic ratio	applies to particle electron
	has equation
	has symbol γe
	has uncertainty 0.000000071 × 1011 s-1 T-1
	has value 1.760859794 × 1011 s-1 T-1
	is an instance of particle g factor
electron magnetic moment	applies to particle electron
	has symbol μe
	has uncertainty 0.000037 × 10-26 J T-1
	has value -928.476362 × 10-26 J T-1
	is an instance of particle magnetic moment
electron magnetic moment anomaly	applies to particle electron
	has equation
	has symbol ae
	has uncertainty 0.0000000041 × 10-3
	has value 1.1596521869 × 10-3
	is an instance of particle magnetic moment anomaly
electron mass	applies to particle electron
	has symbol me
	has uncertainty 0.00000072 × 10-31 kg
	has value 9.10938188 × 10-31 kg
	is an instance of particle mass
electron temperature	has definition The temperature that appears in the Maxwell distribution of velocities for electrons.
	is a kind of temperature
electron volt	has definition Unit employed to indicate the energy of a charged particle in terms of the energy received by the charge on an electron due to a potential difference of one volt. An approximate value (1 in 104) for the energy of electromagnetic radiation expressed in electron volts is given by 1234 / λ, where λ is the wavelength in nanometres. In recent years it has become customary to write MeV and GeV for mega (106) and giga (109) electron volts. In the USA 109 electron volts are often written as BeV, the letter B being used in this case as an abbreviation for the American billion (109), but in 1948 the International Union of Pure and Applied Physics disapproved of the use of BeV and expressed a preference for GeV or 109 eV. The electron volt was called the equivalent volt when it was originally introduced in 1912.
	has definition Unit of energy used in atomic and nuclear physics; the kinetic energy acquired by one electron in passing through a potential difference of 1 volt in vacuum. Sometimes used as a unit of mass (see rest-mass energy)
	has equivalent 160.219 × 10-21 joule
	has symbol eV
	has symbol eV
	is an instance of energy unit
	is an instance of energy unit
	is an instance of non SI unit
	is equivalent to 1.6 × 10-12erg
	is equivalent to 1.6 × 10-19 joules
electrostatic unit	has definition Unit of charge defined as the charge which exerts a force of 1 dyne on a charge of equal magnitude at a distance of 1 cm.
	has symbol esu
	is an instance of charge unit
electroweak	has carrier boson vector boson
	has definition A unification of electromagnetism and the weak nuclear force.
	has definition Responsible for certain kinds of radioactivity; for example, the disintegration of a neutron into a proton, electron, and antineutrino.
	has definition The combination of the electromagnetic force and the weak nuclear force which takes place at high energy.
	has definition The theory that unifies the electromagnetic force and the weak nuclear force into a single force. This theory was developed in the 1960s by Sheldon Glashow, Steven Weinberg, and Abdus Salam and has been subsequently confirmed in the laboratory. One of the mathematical properties of this theory is called the electroweak symmetry.
	has definition The unified description of the weak interactions and electromagnetism, developed between 1967 and 1970 by Sheldon Glashow, Steven Weinberg, and Abdus Salam.
	has definition Theory demonstrating links between the electromagnetic and the weak nuclear forces. Indicates that in the high energies that characterized the very early universe, electromagnetism and the weak force functioned as a single, electroweak force. Also known as the Weinberg-Salam theory.
	has range
	has strength (relative to electromagnetism)
	has synonym weak force
	is a kind of fundamental force
element	has definition Different elements are distinguished by the number of protons in their nuclei. All hydrogen atoms have one proton; all helium atoms have two protons; all oxygen atoms have eight protons.
	has definition The building block of matter. The nucleus of an atom consists of one or more protons and may contain neutrons as well; any electrons surround the nucleus. The number of protons in the atom - the atomic number - determines the element.
	has definition The fundamental unit of a chemical element. An atom consists of a nucleus, which may contain protons and neutrons, and electrons, which occupy shells that surround the nucleus and are centered on it.
	has definition The smallest component of matter that retains its chemical properties. An atom consists of a nucleus and at least one electron.
	has synonym atom
	is a kind of particle
	is a part of Universe
element 110	is a kind of transactinide
element 111	is a kind of transactinide
element 112	is a kind of transactinide
elementary charge	has symbol e
	has uncertainty 0.000000063 × 10-19 C
	has value 1.602176462 × 10-19 C
	is an instance of charge
	is an instance of electromagnetic constant
elementary particle	has definition A particle considered to be fundamental, i.e. not composite, a particle which cannot be separated into components
	has spin
	is a kind of particle
elementary particle symmetry	has definition Abstract mathematical relationships that relate elementary particles together and allow them to be grouped into families. A particular symmetry transformation has the effect of, in a theoretical way, transforming one elementary particle into another.
	is a kind of symmetry
	is a kind of unitary transformation
elevation	has definition Angular distance above the horizon.
	has definition The angle in degrees above the horizon toward the zenith or overhead point. Sometimes loosely called the "altitude" of a star, but not to be confused with height above sea level. Elevation angle is 90° minus the zenith distance (or zenith angle).
	has definition The angular distance of a celestial body above or below the horizon, measured along the great circle passing through the body and the zenith. Elevation is 90 deg. minus zenith distance.
	has synonym altitude
	is an instance of angle
	is an instance of local coordinate component
eleven-dimensional supergravity	has definition Promising higher-dimensional supergravity theory developed in the 1970s, subsequently ignored, and more recently shown to be an important part of string theory.
	is a kind of supergravity
ELF band	has frequency 300 Hz to 3 kHz
	has wavelength 100 km to 1000 km
	is a kind of radio
ellipse	has definition A plane curve in which the sum of the distances of each point along its periphery from two points - its "foci" - are equal.
	is a kind of conic section
elliptical galaxy	has classification criteria E0 (spherical) to E7 (greatest eccentricity)
	has definition A galaxy with an ellipsoidal shape, without spiral arms. Ellipticals have little interstellar matter and no blue giants - the only giants are red, and they give ellipticals a slightly redder color than spirals. Ellipticals apparently produce only Type I supernovae.
	is a kind of galaxy
elliptical orbit	has amplitude equal to the semimajor axis
	has parameters orbital element
	has period proportional to the orbital period
	is a kind of ellipse
	is a kind of harmonic motion
	is a kind of orbit
elongation	has elongation
	is a kind of angle
emersion	has definition The reappearance of a celestial body after eclipse or occultation.
	is a kind of occultation phase
	is preceeded by transit
emission	has definition The process of transition of an electron from an outer orbit to an inner orbit around the nucleus results in a characteristic amount of energy being radiated (as line emission) that corresponds to the lost energy of the electron.
	has inverse process absorption
	is a kind of radiation intensity modification
emission line	has antonym absorption line
	has definition Bright line superposed on a continuous spectrum. Can be produced in the laboratory by a glowing gas under low pressure.
	has definition Bright lines produced in a spectrum by a luminous source, such as a star or a bright nebula.
	is a kind of spectral line
emission line galaxy	has emission lines
	is a kind of galaxy
emission line star	has emission line
	is a kind of star
empiricism	has definition An emphasis on sense data as a source of knowledge, in opposition to the rationalist belief that reasoning is superior to experience.
	is a kind of doctrine
Enceladus	has definition Third satellite of Saturn
	has diameter 500 km
	has discoverer Herschel
	has discovery date 1789
	has orbital period 1.37 days
	is a part of Saturn
	is an instance of natural satellite
Encke's comet	has definition The comet with the shortest known period (3.30 years) (a = 2.21 AU, e = 0.847, i = 12°.4). It has been observed at every apparition since its discovery in 1819. Its period is gradually decreasing. Named after J. F. Encke, who computed its orbit. (It was discovered by Pons.)
	is a part of our solar system
	is an instance of comet
Encke's division	has definition A region of decreased brightness in the outermost ring of Saturn.
	has definition Gap within Saturn's A ring.
	is a kind of ring gap
	is a part of Saturn ring system
endothermic fusion process	has definition a fusion process which requires energy
	is a kind of energy sink
	is a kind of fusion
energy	has unit energy unit
	is a kind of quantity
energy level	has definition Allowed energy state for electrons orbiting the nucleus of an atom.
	has definition Any of the several discrete states of energy in which an atom or ion can exist. For example, an orbital electron can exist only in those energy levels that correspond to an integral number of deBroglie wavelengths in a Bohr atom.
	is a kind of energy
energy sink	is a kind of physical phenomena
energy source	is a kind of physical phenomena
energy unit	has definition (1) The capacity to do work. (2) Manifestation of a particular variety of force.
	is a kind of unit
	is a unit of energy
English equatorial telescope	has mounting English equatorial
	is a kind of equatorial telescope
enthalphy	has definition The heat content of a body. H = U + pV, where U is the internal energy, p is the pressure, and V is the volume.
	has symbol H
	is a kind of energy
eocene epoch	has duration 22 million years
	has start time 58 million years ago
	is a kind of tertiary period
ephemeris second	has definition The length of a tropical second (1/31556925.97474 of the tropical year) on 1900 January 0.5 ephemeris time.
	has value 1/31556925.97474 tropical year
	is an instance of second unit
epicycle	has definition A means of accounting for the apparent motions of the planets in terms of circular motions in a geocentric cosmology. Each planet moves in a circle, the center of which moves in a circle of larger radius, and so on, the largest circles being centered on the earth.
	has definition Circular orbit of a body round a point that is itself in a circular orbit round a parent body. Such a system was formulated to explain some planetary orbits in the Solar System before they were known to be elliptical.
	has definition In Ptolemaic cosmology a circular orbit around a point that itself orbits another point.
	is a kind of outdated belief
epoch	has definition A date and time that specifies the reference system to which celestial coordinates are referred. Prior to 1984 coordinates of star catalogs were commonly referred to the mean equator and equinox of the beginning of a Besselian year. Beginning with 1984 the Julian year has been used, as denoted by the prefix J, e.g., J2000.0.
	has definition A point of time selected as a fixed reference.
	has definition An arbitrary fixed instant of time or date used as a chronological reference datum for calendars (see calendar), celestial reference systems, star catalogs, or orbital motions (see orbit).
	has definition An orbital element representing the time of perihelion passage.
	has symbol T
	is an instance of orbital element
	is an instance of time
epsilon Aurigae	has definition An eclipsing binary with an invisible supergiant companion. The primary is an extremely luminous A8 Ia supergiant of 30 Msun in a post-main-sequence stage of evolution; the secondary may be a collapsed star or black hole. It has at least six components.
	has distance 1 kpc
	has orbital period 27 years
	has primary A8 Ia
	is a part of Auriga
	is an instance of eclipsing binary
	is an instance of white supergiant
Epsilon Eri	has apparent magnitude 4
	has definition In 1973 van de Kamp announced that this star has a planet-like object in orbit around it at a distance of about 8 AU and with a period of about 25 years.
	has distance 3.30 pc
	has spectral type K2 V
	is a part of Eridanus
	is an instance of dwarf
	is an instance of K star
Epsilon Eridani	has definition A young orange dwarf star that is visible to the naked eye.
	has distance 10.7 light-years
	is a part of Eridanus
	is an instance of dwarf
Epsilon Indi	has definition An old orange dwarf star in the southern constellation Indus.
	has distance 11.2 light-years
	is an instance of dwarf
Epsilon Pegasi	has B-V magnitude 1.53
	has declination +9 52 30
	has right ascension 21 44 11.1
	has spectral type K2Ib
	has synonym HR 8308
	has V magnitude 2.39
	is a part of Pegasus
	is an instance of K star
	is an instance of naked eye star
	is an instance of supergiant
Epsilon Sagittarii	has B-V magnitude -0.03
	has declination -34 23 5
	has right ascension 18 24 10.3
	has spectral type B9.5III
	has synonym HR 6879
	has V magnitude 1.85
	is a part of Sagittarius
	is an instance of B star
	is an instance of giant
	is an instance of naked eye star
Epsilon Ursae Majoris	has B-V magnitude -0.02
	has declination +55 57 35
	has right ascension 12 54 1.7
	has spectral type A0pCr
	has synonym HR 4905
	has V magnitude 1.77
	is a part of Ursa Major
	is an instance of A star
	is an instance of naked eye star
equator	has definition The great circle on the surface of a body formed by the intersection of the surface with the plane passing through the center of the body perpendicular to the axis of rotation. (See celestial equator.)
	is a kind of plane
equatorial coordinate	has component equatorial coordinate component
	has declination
	has right ascension
	is a kind of coordinate
equatorial coordinate component	is a component of equatorial coordinate
	is a kind of coordinate component
equatorial sky area	has definition A fixed region on the sky defined using equatorial coordinates
	is a kind of quantity
	is defined using equatorial coordinates
equatorial telescope	has definition The classic type of telescope mount with one axis parallel to the Earth's polar axis (i.e. pointing at the celestial pole) and the other at right angles. Once the object is located, only the polar axis need be driven by a motor to counteract the Earth's rotation.
	has mounting equatorial
	is a kind of Earth based telescope
equatorial velocity	has definition The velocity at the surface of a rotating body, on its equator
	is a kind of velocity
equinox	has definition Either of the two points on the celestial sphere at which the ecliptic intersects the celestial equator; also the time at which the Sun passes through either of these intersection points; i.e., when the apparent longitude (see apparent place; celestial longitude) of the Sun is 0° or 180°. (See catalog equinox; dynamical equinox for precise usage.)
	has definition Either of the two points on the celestial sphere where the celestial equator intersects the ecliptic.
	has definition One of two points in the sky that represent where the Sun appears to cross the plane of the Earth's equator. From the Earth's viewpoint therefore, the Sun reaches one point at a quarter, the other at three quarters of the way through the sidereal year: the vernal (spring) equinox is thus on or around 21 March, the autumnal on or around 22 September. The actual points in the sky change slightly every year through a process called precession.
	has period 1 year
	is a kind of periodic celestial event
equivalence principle	has definition Core principle of general relativity declaring the indistinguishability of accelerated motion and immersion in a gravitational field (over small enough regions of observation). Generalizes the principle of relativity by showing that all observers, regardless of their state of motion, can claim to be at rest, so long as they acknowledge the presence of a suitable gravitational field.
	has definition In a freely falling and nonrotating laboratory the laws of physics, including their numerical content, are the same everywhere including gravity-free space.
	has definition States that inertial mass is indistinguishable from gravitational mass.
	has definition The principle that it is impossible to distinguish between gravitational and inertial forces; gravitational mass is precisely equal to inertial mass.
	has definition The statement that a gravitational force is completely equivalent in all of its physical effects to an overall acceleration in the opposite direction. For example, a person in an elevator in space accelerating upward at 32 feet per second per second would feel the floor pushing upward against her feet in exactly the same way as if the elevator were at rest on earth, where gravity pulls downward with an acceleration of 32 feet per second per second. The "weak equivalence principle," which is not as strong as the equivalence principle, states that all objects, independent of their mass or composition, fall with the same acceleration in the presence of gravity. The Eötvös experiment, and later refinements of this experiment, have proven the weak equivalence principle.
	is an instance of gravity law
Equuleus	has acronym Equ
	has boundary
	has genitive Equulei
	has synonym Little Horse
	is a part of celestial sphere
	is an instance of constellation
era	has definition A system of chronological notation reckoned from a given date.
	has duration
	has start time
	is a kind of event
erbium	has image
	has ocean oxidation state III
	has ocean residence time 400 years
	is a kind of rare Earth
	is a kind of recycled oceanic element
erg	has definition Unit of energy; the work done by a force of 1 dyne acting over a distance of 1 cm.
	has equivalent 1 g cm2 s-2
	has equivalent 10-7joules
	has name origin Greek verb 'to work'
	has proposal date 1873
	has proposer British Association
	has synonym dyne cm
	is an instance of CGS unit
	is an instance of energy unit
ergodic motion	has definition Motion by one or more particles which fills phase space with uniform density after a sufficiently long time.
	is a kind of mass motion
Eridanus	has acronym Eri
	has boundary
	has genitive Eridani
	has synonym River Eridanus
	is a part of celestial sphere
	is an instance of constellation
Eros	has asteroid number 433
	has closest approach to Earth < 0.15 AU
	has definition A small Asteroid.
	has diameter 35 × 16 × 17 km
	has discoverer G. Witt
	has discovery date 1898
	has eccentricity e = 0.223
	has inclination i = 10°.8
	has orbital period 642 days
	has perihelion distance 1.084 AU
	has rotation period 5h16m12s.913
	has semi-major axis a = 1.48 AU
	has shape elongated
	is a part of asteroid belt
	is an instance of asteroid
erruptive prominence	has definition A violent prominence which may reach heights of 2 million km
	has height < 2 million km
	is a kind of prominence
ESA satellite	is a kind of artificial satellite
escape velocity	has definition Speed a satellite must attain in order to free itself from returning to the parent body under the effects of gravity.
	has definition The speed at which an object can leave another object behind, without being recalled by its gravitational force. The escape velocity of Earth - which must, for instance, be attained by a spacecraft if it is to reach another planet - is 25,000 miles per hour.
	has definition The velocity that a body requires to achieve a parabolic orbit around its primary (Ve = sqrt(2GM/R)). Escape velocity at Earth's surface is 11.2 km s-1; of Moon, 2.4 km s-1; of Sun, 617.7 km s-1 (cf. orbital velocity).
	is a kind of velocity
ESO 1-meter Schmidt Telescope	has altitude 2318 m
	has aperture 1.00 m
	has creation date 1972
	has focal ratio f/3.06
	has latitude 29° 15' S
	has location La Silla, Chile
	has longitude 70° 44' W
	has mirror diameter 1.6 m
	has mirror maker Zeiss (Ober.)
	has mirror type Schott Duran 50
	has mounting manufacturer Heidenreich & Harbeck
	has owner European Southern Observatory
	has synonym ESO Schmidt
	is an instance of Schmidt
ESO 3.6-meter Telescope	has altitude 2387 m
	has aperture 3.57 m
	has creation date 1977
	has focal ratio f/3.0, 8.1, 32
	has latitude 29° 16' S
	has location La Silla, Chile
	has longitude 70° 44' W
	has mirror maker REOSC
	has mirror type Fused-silica
	has mounting manufacturer Creusot-Loire
	has owner European Southern Observatory
	has synonym ESO 3.6 m
	is an instance of Horseshoe equatorial telescope
	is an instance of optical telescope
	is an instance of reflector
Eta Aquarid	has duration 6 days
	has parent object Comet Halley
	has radiant Eta Aquarii
	has rate 60 per hour
	has start time 4 May
	is an instance of meteor shower
Eta Aquilae	has definition A pulsating star in the constellation Aquila. It was the first Cepheid discovered, in 1784.
	has discovery date 1784
	is a part of Aquila
	is an instance of Population I Cepheid
eta Carinae	is an instance of bright blue variable
Eta Piscium	has B-V magnitude 0.97
	has declination +15 20 45
	has right ascension 1 31 28.9
	has spectral type G7IIIa
	has synonym HR 437
	has V magnitude 3.62
	is a part of Pisces
	is an instance of G star
	is an instance of giant
	is an instance of naked eye star
etalon	has definition Essentially an optical filter that operates by multiple-beam interference of light reflected and transmitted by a pair of parallel flat reflecting plates.
	is a kind of Fabry-Perot interferometer
ethyl alcohol	has symbol C2H5OH
	is an instance of interstellar molecule
ethynyl	is an instance of interstellar molecule
EUMETSAT satellite	has definition meteorological satellite launched and maintained by Europe's Meteorological Satellite Organization
	is a kind of meteorological satellite
Europa	has definition One of the Galilean satellites of Jupiter
	has diameter 3600 km
	has eccentricity e = 0.00
	has inclination i = 0°.01
	has mean density 3.07 g cm-3
	has orbital period 3.55 days -has source: [H76]
	has synonym Jupiter II
	is a part of Jupiter
	is an instance of Galilean satellite
European Southern Observatory	has acronym ESO
	is an instance of observatory
European Space Agency	has acronym ESA
	is an instance of space science institution
European Synchrotron Research Facility	has acronym ESRF
	is an instance of high energy physics institution
europium	has image
	has ocean oxidation state III
	has ocean residence time 500 years
	is a kind of rare Earth
	is a kind of recycled oceanic element
evaporation	has final phase gas
	has initial phase liquid
	has inverse process condensation
	is a kind of first order phase transition
even-odd nucleus	has definition Nucleus that contain even numbers of protons but odd numbers of neutrons.
	is a kind of fermion
	is a kind of nucleus
event	has definition A point in four-dimensional spacetime referenced by three spatial coordinates and a complementary temporal ordinate.
	has duration
	has synonym world point
	has time of occurrence
	is a kind of physical phenomena
Evershed effect	has definition The radial motion outward (from the central umbra) of the gases in the penumbral regions of sunspots.
	is a kind of solar motion
exa	has symbol E
	has value 1018
	is an instance of unit prefix
excitation potential	has definition Amount of energy required to bring an electron from its ground state to a given excited state (measured in electron volts).
	is a kind of energy
exclusion principle	applies to fermion
	has definition Two identical fermions cannot occupy the same quantum state (i.e. cannot have the same charge, spin, momentum, quantum numbers etc. within the same region of space).
	has example No two electrons in an atom can have the same set of values for the four quantum numbers n, l, mb, ms.
	has implication solid objects cannot exist in the same physical space.
	has synonym Pauli exclusion principle
	is an instance of quantum law
exothermic fusion process	has definition A fusion reaction which linerates energy.
	is a kind of energy source
	is a kind of fusion
	liberates energy
expanding arm	has definition A spiral arm of neutral hydrogen receding from the galactic nucleus at about 135 km s-1.
	has distance from galaxy center between 2.5 and 4 kpc
	is a part of disk
expanding emission nebula	has composition enhanced with heavy elements relative to the interstellar medium
	has expansion velocity
	has explosion date
	has progenitor star
	is a kind of gaseous nebula
expansion	is a kind of mass motion
experiment	is a kind of theory related concept
Explorer 22	is an instance of inflatable spacecraft
explosive galaxy formation	has definition A theory of galaxy formation wherein the explosion of a large number of stars creates a giant shock wave that travels outward and compresses the surrounding gas. Galaxies form in the regions of high-density gas.
	is a kind of galaxy theory
explosive nucleosynthesis	has definition The nucleosynthesis processes that are believed to occur in supernovae. Explosive carbon burning occurs at a temperature of about 2 × 109 K and produces the nuclei from neon to silicon. Explosive oxygen burning occurs near 4 × 109 K and produces nuclei between silicon and calcium in atomic weight. At higher temperatures, still heavier nuclei, up to and beyond iron, are produced.
	has definition The nucleosynthetic processes which are thought to occur in supernovae. These explosive processes are thought to produce the nuclei from neon up to and including the e-process nuclei and possibly the r-process nuclei. Explosive carbon burning occurs for a temperature of about 2 × 109 K and a density of 104-107 g cm-3 and produces nuclei from neon to silicon. Explosive oxygen burning occurs for a temperature of about 4 × 109 K and produces nuclei from silicon to calcium, and the e-process occurs at a temperature greater than 5 × 109 K and produces the iron peak nuclei.
	is a kind of stellar nucleosynthesis
exponential expansion	has definition An expansion described by a fixed doubling time. The size doubles after one doubling time, quadruples after two doubling times, octuples after three doubling times, etc.
	has definition Extremely rapid expansion. "Exponential" is a mathematical term that precisely defines the rate of expansion. For example, a balloon that doubles its size every second is expanding exponentially. By contrast, a balloon whose radius is one inch after one second, two inches after two seconds, three inches after three seconds, and so on, is expanding linearly with time, rather than exponentially. According to the inflationary universe model, the early universe went through a brief period of exponential expansion, during which its size increased enormously.
	is a kind of expansion
extinction level event	has average interval time 100 million years
	has definition impact event which can cause the extinction of many species on a planet
	is a kind of impact event
extragalactic astronomy	has definition The field that deals with objects beyond the Milky Way, especially galaxies and quasars.
	is a kind of astronomy
extragalactic globular cluster	is a kind of globular cluster
extremal black hole	has definition Black hole endowed with the maximal amount of force charge possible for a given total mass.
	is a kind of black hole
extreme ultraviolet	has acronym EUV
	is a kind of ultraviolet
extremely red galaxy	has acronym ERG
	is a kind of infrared galaxy
F corona	has definition The outer part of the solar corona which emits a continuous spectrum in which absorption lines can be seen. The F corona is caused by radiation from the photosphere scattered by interplanetary dust, and it decreases slowly with distance from the Sun. (the F stands for Fraunhofer)
	has synonym F component
	is a part of corona
F layer	has definition One of two layers in the Earth's ionosphere immediately above the E layer.
	has synonym Appleton layer
	is a part of ionosphere
F region	has definition Region of the ionosphere above the F layers.
	is a part of ionosphere
F star	has color yellow-white
	has definition Star of spectral type F in which lines of hydrogen and Ca II are of about equal strength. Metal lines also become noticeable.
	has surface temperature 6000 to 7500 K
	is a kind of early star
f-electron	has definition An orbital electron whose l quantum number is 3.
	has orbital quantum number 3
	is a kind of bound electron
f-spot	is a kind of sunspot
F1 layer	has altitude 200 km
	is a part of F layer
F2 layer	has altitude 300 km
	is a part of F layer
Fabry-Perot interferometer	has acronym FP
	has definition A device that measures distances and changes of distance very accurately, using the pattern of overlap of waves of light.
	has definition A type of interferometer wherein the beam of light is passed through a series of pairs of partly reflecting surfaces set at various angles to it and spaced at certain prechosen numbers of the wavelength to be examined. It differs from the Michelson interferometer in that it has only one arm.
	is a kind of spectrograph dispersing element
faculae	has definition Bright areas on the face of the Sun, commonly in the vicinity of sunspots. Named by Johannes Hevelius, they are thought to be caused by luminous hydrogen clouds close to the photosphere.
	has definition Bright regions of the photosphere seen in white light, visible only near the limb of the Sun.
	has lifetime 15 days
	is a part of photosphere
Fahrenheit	has absolute zero -459.67
	has definition A temperature scale based on three fixed temperature points - the temperature of an ice and salt mixture, the freezing point of water and normal human temperature - which were taken to be 0, 32 and 96 respectively. It is mere coincidence that the temperature interval between the freezing (32 °F) and boiling (212 °F) points of water is 180° when expressed in the Fahrenheit scale.
	has proposal date 1710
	has triple point of water 32.018
	is an instance of temperature unit
	is named after G. D. Fahrenheit (1686-1736)
faint blue galaxy	has definition A distant, irregularly shaped galaxy in which a large amount of star formation is taking place.
	is a kind of irregular galaxy
far infrared	has acronym FIR
	has source atomic transitions, rotational transitions in molecules
	is a kind of infrared
farad	has base unit m-2·kg-1·s4·A2
	has symbol F
	has unit C·V-1
	is an instance of capacitance unit
	is an instance of named derived SI unit
Faraday constant	has equation
	has symbol F
	has uncertainty 0.0039 C mol-1
	has value 96485.3415 C mol-1
	is an instance of physico chemical constant
Fechner's law	has definition The intensity of a sensation increases as the logarithm of the stimulus. (See Pogson's ratio.)
	is an instance of law
femto	has symbol f
	has value 10-15
	is an instance of unit prefix
fermi	has approval date 1956
	has definition A unit of distance used for describing nuclear distances just as the ångström is used for atomic distances.
	has definition A unit of length.
	has equivalent 10-13 cm
	has equivalent 10-15 m
	is an instance of length unit
	is named after Enrico Fermi
Fermi coupling constant	has equation
	has symbol Gf/(hc)3
	has uncertainty 0.00001 × 10-5 GeV-2
	has value 1.16639 × 10-5 GeV-2
	is an instance of atomic constant
Fermi level	has definition The maximum energy of any particle in a group of low-temperature subatomic particles called fermions. Fermions, such as electrons, cannot occupy the same space at the same energy. Thus, if many fermions are placed close together, their energies must all be different. The energy of that particle with the largest energy is the Fermi energy of the system.
	is a kind of energy
Fermi National Accelerator Laboratory	has acronym Fermilab
	has definition Home of the Tevatron, the world's most powerful accelerator, a p p bar collider with a maximum collision energy of 1.8 Te V (= 1800 Ge V = 1.8 × 1012 eV).
	has location Batavia, Illinois, USA
	is an instance of high energy physics institution
Fermi-Dirac nuclei	has definition Nuclei of odd A-number (i.e., nuclei that do not have integral spin) (cf. Bose-Einstein nuclei). Fermi-Dirac nuclei therefore obey the exclusion principle (q.v.).
	is a kind of nucleus
Fermi-Dirac-Sommerfeld law	has acronym FDS
	has definition A law which gives the algebraic number of a quantized system of particles which have velocities within a small range.
	is an instance of quantum law
fermion	has definition A particle, or pattern of string vibration, with half a whole odd number amount of spin; typically a matter particle.
	has definition An elementary particle whose spin is a half-integral multiple of h/2π. Fermions include the baryons, the leptons and their antiparticles, and obey the Pauli exclusion principle (cf. boson).
	has definition Any particle with half-integer spin: 1/2 h bar, 3/2 h bar, 5/2 h bar, etc. All fermions obey Pauli's exclusion principle.
	has definition Elementary particle with fractional spin. The proton, electron, neutron, and other elementary particles are all fermions.
	has definition Particle with half-integral spin. Fermions obey the exclusion principle, which says that no two fermions can exist in an atom in the same quantum state; in practice this restricts the number of electrons, which are fermions, permitted in each electron shell.
	has quantum behavior Fermi-Dirac statistics
	has spin half-integral
	is a kind of particle
	obeys exclusion principle
fermium	is a kind of transuranium element
fibrille	has definition Striation or streak which is observed to form whirls in the solar chromosphere.
	is a part of chromosphere
field galaxy	has definition An isolated galaxy which does not belong to any cluster of galaxies. The ratio of galaxies in clusters to field galaxies is about 23:1.
	is a kind of galaxy
field horizontal branch star	has definition High-velocity metal-weak star of either B or A spectral type.
	has spectral type B star or A star
	is a kind of Population II star
field lens	has definition A lens placed in or near the focal plane of a telescope to create an image of the primary mirror inside the instrument.
	is a kind of lens
field star	has definition A star that is not part of any star cluster. Most stars, including the Sun, are field stars.
	has definition Star distributed at random in space and not belonging to any particular star cluster.
	is a kind of star
filament	has definition A prominence seen in projection on the solar disk.
	is a kind of prominence
fine structure	has definition Splitting of spectral lines by the spin-orbit energy - i.e., the potential energy of the inherent electron magnetic moment in the atom's own magnetic field.
	is a kind of set of lines
fine-structure constant	has definition A "coupling constant," e2 / h bar c, approximately 1/137, that measures the strength of an interaction between a charged particle and the electromagnetic field. It gives a rough measure of the relative importance of relativistic and spin effects in the spectra of atoms.
	has definition A coupling constant e2 / h bar c, approximately equal to 1/137 (where e is the electron charge, h bar is Plancks constant, and c is the speed of light), that measures the strength of the interaction between a charged particle and the electromagnetic field.
	has definition A parameter that measures the strength of the electromagnetic force. The fine-structure constant is a combination of other fundamental constants of nature - the electrical charge of the electron, the speed of light, and Planck's constant of quantum mechanics.
	has equation
	has symbol α
	has symbol α
	has uncertainty 0.000000027 × 10-3
	has value 7.297352533 × 10-3
	is an instance of atomic constant
fine-tuning	has definition A phrase meaning a highly constrained and implausible adjustment of the parameters of a theory.
	is a kind of theory related concept
fireball	is a kind of meteor event
FIRST	has definition Far-InfraRed Space Telescope.
	is an instance of infrared space telescope
first law of thermodynamics	has definition The law of conservation of energy
	is an instance of thermodynamics law
first order phase transition	has definition A phase transition which occurs in a manner similar to the way water boils. Bubbles of the new phase (steam) form in the midst of the old phase (water), so that temporarily the two distinct phases (steam and water) coexist.
	has final phase
	has initial phase
	is a kind of phase transition
first point of Aries	is an instance of ecliptic coordinate
first radiation constant	has equation
	has symbol c1
	has uncertainty 0.00000029 × 10-16 W m2
	has value 3.74177107 × 10-16 W m2
	is an instance of physico chemical constant
fission	has antonym fusion
	has definition In nuclear physics, the splitting of the atomic nucleus of a heavy element, resulting in the emission of nuclear energy and possibly causing a chain reaction (with similar results) within a mass of the element.
	has definition Interaction in which nucleons previously united in an atomic nuclei are disjoined, releasing energy. Fission powers atomic bombs.
	is a kind of nuclear process
fission of stable elements lighter than iron	is a kind of energy sink
five-minute oscillations	has definition Vertical oscillations of the solar atmosphere with a well-defined period of 5 minutes.
	is a kind of harmonic motion
	is a kind of solar motion
fixed mount telescope	has mounting fixed direction
	is a kind of Earth based telescope
fixed vertical mount telescope	has mounting fixed vertical
	is a kind of fixed mount telescope
flare star	has definition A member of a class of dwarf stars (usually dM3e-dM6e) that show sudden, intense outbursts of energy. The flares are usually rare and very short with mean amplitudes of about 0.5-0.6 mag. All known flare stars are intrinsically faint and have emission lines of H I and Ca II. It is generally believed that flares in flare stars have certain properties in common: rapid rise to peak light followed initially by a rapid decline and later by a slower phase that occasionally does not return to a preflare level within practical monitoring times (several hours). An increase in radio emission is often detected simultaneously with the optical outburst. About 30 flare stars are known, all within 20 pc. (In at least one theory, the flare star stage directly follows the T Tauri stage.)
	has definition A star that emits flares, which can outshine the entire star. Many red dwarfs are flare stars.
	has definition Dim red dwarf star that suddenly lights up with great - but brief - luminosity, corresponding to an equally powerful but short-lived burst of radio emission. The cause is thought to be a sudden and intense outburst of radiation on or above the star's surface.
	has definition Stars undergoing erratic jumps in brightness (up to a few magnitudes) on time scales of the order of minutes. During the quiescent phase the spectrum is that of an M dwarf with emissions in the CaII and Balmer lines.
	has synonym UV Ceti star
	is a kind of cataclysmic variable
	is a kind of radio star
	is a kind of red dwarf
flat universe	has definition A cosmological model in which a static (neither expanding nor collapsing) universe is maintained by introducing a cosmological repulsion force (in the form of the cosmological constant) to counterbalance the gravitational force.
	has definition A Friedmann model of the Universe in which the spacetime continuum is not curved.
	has definition A homogeneous world model (the simplest relativistic model) of finite density, zero curvature, and nonzero cosmological constant, subject to the field equations of general relativity in an expanding Euclidean space. The radius increases rapidly from zero, and, although it always increases, the rate of increase becomes less as time goes on.
	has definition A homogeneous, isotropic universe is called flat if it is just on the borderline between being spatially closed and spatially open, so the geometry is precisely Euclidean. If Einstein's cosmological constant is zero, then a flat universe will go on expanding forever, but the velocity of recession between any two objects would approach zero at large times.
	has definition A particular solution to Einstein's cosmological equations in which the universe is flat. (See flat universe.)
	has definition A Universe in which there is no curvature to the spacetime continuum. This means that the kinetic energy of the expansion is exactly balanced by the potential gravitational energy of the matter. Thus, after an infinite amount of time the Universe will stop expanding.
	has definition A universe that is at the boundary between an open and closed universe. In a flat universe, the average mass density always has precisely the critical value. A flat universe has zero total energy and an infinite size. Flat universes have the geometry of an infinite, flat surface, that is, Euclidean geometry. The value of omega is 1 for a flat universe. (See closed universe; critical mass density; Euclidean geometry; omega; open universe.)
	has definition A world model of a static universe with a positive cosmological constant, whose radius of curvature is constant and independent of time.
	has definition Big Bang model that was formulated by Friedmann and Lemaitre which has a zero curvature, or flat (Euclidian). This space is unbounded.
	has definition The flat (k = 0), pressureless standard model of the universe.
	has definition The Friedmann-Lemaitre model in which space is Euclidean was advocated by Einstein and de Sitter in 1932.
	has geometry of space flat or Euclidian
	has synonym Einstein-de Sitter universe
	is a kind of big bang
flatness problem	has definition A problem of the traditional big bang theory (without inflation) related to the precision required for the initial value of omega, the ratio of the actual mass density to the critical mass density. If the description is started at one second after the big bang, for example, omega must have been equal to one to an accuracy of fifteen decimal places, or else the resulting universe would not resemble our own. Yet the traditional big bang theory offers no explanation for this special value, which must be incorporated as an arbitrary postulate about the initial conditions. See also horizon problem.
	has definition Poses the question: why, out of an infinite number of possibilities, is our Universe so close to the one special case: the "flat" Universe?
	has definition The puzzle of why the universe today is so close to the boundary between open and closed, that is, why it is almost flat. Equivalently, why should the average mass density today be so close to the critical mass density, but not exactly equal to it? If omega begins bigger than 1, it should get bigger and bigger as time goes on; if it begins smaller than 1, it should get smaller and smaller. For omega to be near 0.1 today, about 10 billion years after the big bang, it had to be extraordinarily close to 1 when the universe was a second old. Some people consider such a fine balance to have been highly unlikely according to the standard big bang model, and thus are puzzled as to why the universe today is almost flat. (See closed universe; critical mass density; flat universe; open universe.)
	has definition The riddle of why the universe is neither dramatically open nor closed, but appears to be almost perfectly balanced between these states.
	is a kind of problem
flavor	has definition Designation of quark types - up down, strange, charmed, top, and bottom. Flavor determines how the weak nuclear force influences quarks.
	has definition In particle physics, another word for "type". For example, there are 6 flavors of quarks, meaning that there are 6 different types of quarks.
	has definition The known quarks exist in six different types, or flavors: up, down, charmed, strange, top, and bottom. The up and down quarks belong to the first generation, the charmed and strange quarks belong to the second, and the top and bottom quarks belong to the third. The up, charmed, and top quarks each have an electrical charge 2/3 that of a proton, while the down, strange, and bottom quarks have a charge -1/3 that of a proton. See Table 7.1 on page 120.
	has definition The term used to describe different quark types. There are six quark flavors: up, down, strange, charm, bottom and top.
	is an instance of quantum quantity
Flexible image transport system	has acronym FITS
	has definition A method for saving image data which has become standard in astronomy.
	is an instance of data standard
fluorescence	has definition The absorption of a photon of one wavelength and reemission of one or more photons at longer wavelengths, especially the transformation of ultraviolet radiation into visible light.
	has definition The emission of light at one wavelength, the green say, following absorption of light with a much shorter wavelength such as the ultraviolet. The UV photon parts with its energy by ejecting the electron into a high-energy level from which it cascades back down, releasing photons of lower energy and therefore longer wavelengths. A material which has this property is called a phosphor.
	is a kind of bound-bound transition
	is a kind of emission
fluorine	has abundance 0.4 × 10-4 p.p.m. in deep Pacific seawater
	has abundance 0.96 × 10-4 p.p.m. in deep Atlantic seawater
	has abundance 1.0 × 10-4 p.p.m. in Atlantic surface seawater
	has abundance 1.0 × 10-4 p.p.m. in Pacific surface seawater
	has abundance 3.63 × 104 in Sun relative to H = 1 × 1012
	has abundance 950 p.p.m. in Earth's crust
	has atomic emission line 690.248 nm for F I
	has atomic emission line 703.747 nm for F I
	has atomic emission line 712.789 nm for F I
	has atomic emission line 685.603 nm for F I (strong)
	has atomic number 9
	has atomic radii 70.9 pm
	has biological role essential in trace quantities for mammals, including humans, in the form of fluoride (F-)
	has boiling point 85.01 K
	has chief source fluorite
	has covalent radii 58 pm
	has critical pressure 5573 kPa
	has critical temperature 144.3 K
	has crystal cell dimension a = 550, b = 328, c = 728 pm, β = 102.17 deg for α-F2
	has crystal cell dimension a = 667 pm for β-F2
	has crystal type cubic for β-F2
	has crystal type monoclinic for α-F2
	has daily dietary intake 0.3 - 0.5 mg
	has definition pale yellow gas (F2) which is the most reactive of all the elements, and is the strongest oxidizing agent
	has density 1.696 kg m-3 for gas at 273 K
	has density 1516 kg m-3 for liquid at 85.01 K boiling point
	has discoverer H. Moissan
	has discovery date 1886 (isolated)
	has discovery location Paris, France
	has electron affinity 328 kJ mol-1 from F to F-
	has electron configuration [He]2s22p5 in ground state
	has electronegativity 3.98 Pauling
	has hazard gas is highly corrosive and toxic, low concentration exposure can cause eye and lung irritation
	has hazard metal florides are very toxic
	has hazard organic fluorides are often quite harmless
	has heat capacity 22.744 J K-1 mol-1 for atomic gas at constant pressure 0.1 MPa at 298.15 K
	has heat capacity 31.30 J K-1 mol-1 for molecular gas (F2) at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 5.10 kJ mol-1
	has heat of vaporization 6.548 kJ mol-1
	has image
	has ionic radii 133 pm for F-
	has isotope mass range 17 to 23
	has lethal intake 185 p.p.m. for 1 hour F2 inhalation for rat
	has lethal intake 5 - 25 g NaF
	has lethal intake 5 - 25 g NaF
	has lethal intake 52 mg kg-1 NaF ingestion for rat
	has level in humans 0.05 p.p.m. in muscle
	has level in humans 0.22 - 7 p.p.m. in liver
	has level in humans 0.5 mg dm-3 in blood
	has level in humans 2000 - 12000 p.p.m. in bone
	has longest lived isotope fluorine 19
	has main mining area Canada, USA, UK, Russia, Mexico, Italy
	has mass absorption coefficient 1.80 cm2 g-1 for MoKalpha X-ray diffraction
	has mass absorption coefficient 16.4 cm2 g-1 for CuKalpha X-ray diffraction
	has mass of element in person 2.6 g for a 70 kg average person
	has melting point 53.53 K
	has mineral apatite, cryolite, fluorite
	has molar volume 18.05 cm3
	has name origin fluere = to flow from Latin
	has neutron scattering length 0.5654 × 10-12 cm
	has number of isotopes 7 including nuclear isomers
	has number of protons 9
	has ocean oxidation state -I
	has ocean residence time 400000 years
has pronunciation floor-een
has registry number 7782-41-4 for Chemical Abstracts System database
has relative atomic mass 18.9984032 in units of 12C = 12.000
has reserves 123 × 106 tonnes
has space group C2/m for α-F2
has space group Pm3n for β-F2
has specimen not available for sale as pure gas because it is too reactive and dangerous
has symbol F
has synthesis mechanism electrolysis of molten KF·2HF
has term symbol 2P3/2 in ground state
has thermal conductivity 0.0248 W m-1 K-1 at 273 K
has thermal conductivity 0.0279 W m-1 K-1 at 300 K
has thermal neutron capture cross section 0.0096 barns
has toxic intake 250 mg NaF
has uses AlF3 in aluminium production
has uses CaF2 as a flux in metallurgy
has uses fabrication of UF6, SF6 and fluorinating agents such as ClF3
has uses polymers, pesticides and antibiotics
has van der Waals radii 135 pm
has world production 2400 tonnes year-1 for gas (F2)
has world production 4.7 × 106 tonnes year-1 for fluorite (CaF2)
is a kind of accumulating oceanic element
is a kind of gaseous element
is a kind of halogen
reacts with almost everything violently
fluorine 17	has atomic mass 17.002095
	has decay mode β+ (2.761 Mev)
	has decay mode no γ
	has half life 64.5 seconds
	has nuclear magnetic moment μ = +4.722 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 5/2+ h/2π
	has number of neutrons 8
	has number of nucleons 17
	has symbol 17F
	is an instance of fluorine
fluorine 18	has atomic mass 18.000937
	has decay mode β+ EC (1.655 Mev) 97%
	has decay mode no γ
	has half life 1.83 hours
	has nuclear spin I = 1+ h/2π
	has number of neutrons 9
	has number of nucleons 18
	has symbol 18F
	has uses medical diagnosis
	has uses research
	is an instance of fluorine
fluorine 19	has atomic mass 18.99840322
	has magnetogyric ratio 25.1665 × 107 rad T-1 s-1
	has natural abundance 100%
	has NMR frequency 94.077 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 4730 where 13C = 1.00
	has nuclear magnetic moment μ = +2.628867 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 1/2+ h/2π
	has number of neutrons 10
	has number of nucleons 19
	has relative NMR sensitivity 0.83 with CFCl3 reference where 1H = 1.00
	has symbol 19F
	has uses Nuclear Magnetic Resonance
	is an instance of fluorine
fluorine 20	has atomic mass 19.999981
	has decay mode β- (7.029 Mev)
	has decay mode γ
	has half life 11.0 seconds
	has nuclear magnetic moment μ = +2.094 nuclear magnetons with diamagnetic correction
	has nuclear spin I = 2+ h/2π
	has number of neutrons 11
	has number of nucleons 20
	has symbol 20F
	is an instance of fluorine
FOC	has definition Faint Object Camera (Hubble).
	is a kind of integrating detector
focal reducer	has definition An optical component or system for changing the image scale of a telescope to achieve a better match between the seeing disk and the pixel size. See optical matching.
	has wavefront modification shape
	is a kind of wavefront modifier
focus	is a kind of optical device
Fomalhaut	has B-V magnitude 0.09
	has declination -29 37 20
	has definition An A star. The brightest star in the constellation Piscis Austrinus.
	has distance 7 pc
	has right ascension 22 57 39.0
	has spectral type A3 V
	has synonym alpha PsA
	has synonym HR 8728
	has V magnitude 1.16
	is a part of Pisces Australis
	is an instance of A star
	is an instance of dwarf
	is an instance of naked eye star
forbidden line	has definition Spectral line emitted from a metastable state (q.v.), or those which have a very low probability (10-9-10-10) of occurrence. They appear at particle densities ≤ 108 cm-3. All forbidden lines have low excitation potentials. Forbidden lines are designated by enclosing them in brackets, e.g., [O II].
	has synonym nebular line
	is a kind of emission line
Forbush decrease	has definition A decrease in cosmic-ray intensity during active Sun.
	has discoverer Forbush
	has discovery date 1954
	has period 11 years
	is an instance of periodic celestial event
	is an instance of solar event
force	has carrier boson
	has range
	has strength (relative to electromagnetism)
	is a kind of physical phenomena
force quantity	has definition Agency responsible for a change in a system. In Newtonian mechanics, gravitational force bends the moon away from the straight trajectory it would otherwise pursue.
	has unit force unit
	is a kind of quantity
force unit	is a kind of unit
	is a unit of force quantity
Fork equatorial telescope	has mounting equatorial fork
	is a kind of equatorial telescope
formaldehyde	has definition An organic molecule, the first polyatomic molecule to be discovered in interstellar space. In 1973 It was discovered in two external galaxies.
	has discovery in space date 1969
	has symbol H2CO
	is an instance of interstellar molecule
formamide	has definition An interstellar molecule discovered in space at a wavelength of 6.5 cm.
	has discovery in space date 1971
	has symbol HCONH2
	is an instance of interstellar molecule
formic acid	has definition The first organic acid to be detected in interstellar space at 18.3 cm. Formic acid is the "sting" of an insect.
	has discovery in space date 1970
	has symbol H2CO2
	is an instance of interstellar molecule
Fornax	has acronym For
	has boundary
	has genitive Fornacis
	has historical origin the laboratory Furnace or chemical furnace in honor of Antoine Lavoisier
	has synonym Furnace
	is a part of celestial sphere
	is an instance of constellation named by de Lacaille
Fornax A	has apparent magnitude 10
	has synonym NGC 1316
	is a part of Fornax
	is an instance of radio galaxy
	is an instance of S0 galaxy
Fornax galaxy	has definition A dwarf spheroidal galaxy, in the Local Group, that orbits the Milky Way. (Mv ≈ -12).
	has discovery date 1938
	has distance 190 kpc
	has distance from galaxy center 440000 light-years
	has mass 2 × 107 Msun
	is a part of Fornax
	is a part of Local Group
	is an instance of satellite galaxy
	orbits Milky Way
Four-shooter	has definition An astronomical instrument comprised of four highly sensitive photoelectric cells (CCDs). The four-shooter is placed at the end of a telescope and used to electronically record incoming light.
	is a kind of charge-coupled device
Fourier Transform Spectrometer	has acronym FTS
	is a kind of spectrograph
Fourier transformation	has acronym FT
	is a kind of transformation
fractal	has definition A geometric figure in which a pattern is repeated ad infinitum on smaller and smaller scales. A classic example is Von Koch's snowflake, for which the construction begins with an equilateral triangle. Trisect each side, and replace the middle section by two sides of a smaller equilateral triangle, bulging outward. The snowflake is obtained by repeating this process for each side of the resulting figure, then for each side of the subsequent figure, and continuing forever.
	has definition A pattern that repeats itself or nearly repeats itself on many different scales of magnification. For example, suppose that some ink on a piece of paper appears to form a star. If you look at the piece of paper with a magnifying glass, you see that the dark areas are not solid black, but are formed of tiny stars themselves. If you look at one of these small stars with a microscope, you see that the dark areas of each of the tiny stars is formed from an arrangement of even tinier stars. Such a repeating pattern of stars would be called a fractal.
	has dimensions fractional
	is a kind of geometrical object
frame of reference	has acceleration
	has definition A set of axes to which positions and motions in a system can be referred.
	has rotation rate
	is a kind of mathematical concept
frame transfer	has definition A CCD construction in which one half of the imaging area of the device is purposely covered with a mask opaque to light to provide a temporary charge storage section.
	is a kind of charge-coupled device
francium	has image
	is a kind of alkali metal
Fraunhofer line	has definition Absorption line in the spectrum of the Sun, studied by Fraunhofer in 1814. The nine most prominent he labeled with capital letters (from the red end) A. B. C. D. E. F. G. H. and K. The A band and B band are now known to be groups of telluric lines due to O2 absorption in Earth's atmosphere, and C and F are respectively known as Hα and Hβ.
	has dicovery date 1814
	has discoverer Joseph Fraunhofer
	is a kind of absorption line
	occurs in Sun
free electron	has definition Electron not bound to a nucleus.
	is a kind of electron
free parameter	has definition A number which is needed to define a theory well enough so that predictions can be made, but which must be determined by experiment or observation.
	is a kind of theory related concept
free-fall	has definition A collapse in which gas clouds do not hit or impede one another. According to ELS, the Galactic halo formed in a free-fall collapse.
	is a kind of collapse
free-free transition	has definition The acceleration of an unbound (or free) electron by a proton or atomic nucleus results in the emission of electromagnetic radiation.
	is a kind of atomic process
frequency	has definition Number of oscillations per second of an electromagnetic wave. The amplitude of a wave depends on the intensity; the wavelength, on the frequency.
	has definition The number of complete wave cycles a wave completes each second.
	has definition The number of cycles or complete alternations per unit time of a carrier wave, band, or oscillation.
	has definition The number of oscillations or wave cycles per second passing a given point. For electromagnetic radiation, the product of the frequency and the wavelength is the speed of light.
	has definition The number of peaks (often called crests) of a propagating wave that cross a given point in a unit of time. For example, if 1000 peaks cross a given point in one second, one says that the frequency is 1000 cycles per second or 1000 hertz.
	has symbol ν
	has unit frequency unit
	is a kind of quantity
frequency distribution	has definition A statistical arrangement of numerical data according to size or magnitude (see also distribution function).
	is a kind of statistical distribution
frequency unit	is a kind of unit
	is a unit of frequency
FU Ori star	has definition A kind of T Tau stars with considerable changes in brightness. The post-eruption spectrum is that of a late supergiant.
	has synonym fuors
	is a kind of T Tauri star
Fundamental Catalog	has acronym FK
	is a kind of star catalog
fundamental force	has definition One of four fundamental forces which mediate particle interaction.
	is a kind of force
fundamental frequency	has definition The lowest characteristic frequency of oscillation of a dynamical system.
	is a kind of frequency
fundamental physical constant	has accuracy
	has unit
	has value changes in value are due solely to an increase in measurement accuracy or convention
	is a kind of constant
fundamental star	has definition Star for which coordinates have been determined to a very high degree of accuracy.
	is a kind of star
Fused-quartz	is a kind of mirror
fusion	has antonym fission
	has catalyst
	has definition In nuclear physics, the combining of the atomic nuclei of lighter elements to form nuclei of a heavier element. Such a process involving the atomic nuclei of elements lighter than iron is accompanied by the emission of energy; for fusion of heavier elements, energy must be supplied. The process is thought to contribute to the condensation of stars from interstellar gas and dust. See also nuclear fusion.
	has definition Interaction in which nucleons are forged together, creating new atomic nuclei and releasing energy. Fusion powers hydrogen bombs.
	has definition Process by which the Sun (and other stars) radiates energy. The nucleus of an atom fuses with the nuclei of other atoms to form new, heavier atoms at the same time releasing large amounts of energy. In the Sun, hydrogen atoms are converted into helium by this process, with carbon and nitrogen as intermediates. Cooler stars undergo the proton-proton cycle with a similar result.
	has minimum temperature
	has product
	has reactant
	has reaction probability
	is a kind of nuclear process
	produces energy
fusion device	is a kind of instrument
G band	has definition A band of CH. It is conspicuous in the spectra of G-K stars.
	has species CH
	has wavelength 4303 Å
	is a kind of Fraunhofer line
	is a kind of molecular band
	occurs in G star, K star
G star	has color yellowish
	has definition Spectral type for yellow stars.
	has definition Yellowish star in which the H and K lines of Ca II have become dominant and in which a tremendous profusion of spectral lines of both neutral and ionized metals, particularly iron, begins to show. The Balmer lines of hydrogen are still recognizable. Examples are the Sun and Capella.
	has surface temperature 5000 to 6000 K
	is a kind of late star
G1	has image
	has synonym Mayall II
	is a part of Andromeda galaxy
	is an instance of extragalactic globular cluster
gadolinium	has image
	has ocean oxidation state III
	has ocean residence time 300 years
	is a kind of rare Earth
	is a kind of recycled oceanic element
galactic astronomy	has definition The study of the Milky Way.
	is a kind of astronomy
galactic center	has definition Now thought to comprise black holes - which would explain why the centre of our Galaxy appears strangely obscure, and emits only infrared radiation.
	has definition The direction of the sky toward the center of the Milky Way.
	has galactic latitude 0
	has galactic longitude 0
	is a part of galactic nucleus
	is a part of Sagittarius
	is an instance of galactic coordinate
	is opposite of anticenter
galactic coordinate	has component galactic coordinate component
	has definition A system of coordinates based on the mean plane of the Galaxy, which is inclined about 63° to the celestial equator. Galactic latitude (b) is measured from the galactic equator north (+) or south (-); galactic longitude (l) is measured eastward along the galactic plane from the galactic center. In 1958, because of increased precision in determining the location of the galactic center, a new system of galactic coordinates was adopted, with the origin at the galactic center in Sagittarius at α(1950) = 17h42m.4, δ(1950) = - 28°55'. The new system is designated by a superior roman numeral II (i.e., bII, lII) and the old system by a superior roman numeral I: lII ≈ lI + 32°.31. Galactic coordinates are independent of precession.
	has galactic latitude
	has galactic longitude
	is a kind of coordinate
galactic coordinate component	is a component of astronomical coordinate
	is a kind of coordinate component
galactic equator	has definition The primary circle defined by the central plane of the Galaxy.
	is a kind of equator
galactic latitude	has definition The angle between the line of sight to a star and the Galactic plane. Galactic latitude ranges from +90 degrees to -90 degrees; the Galactic plane has a Galactic latitude of 0 degrees. Regions north of the Galactic plane have positive Galactic latitude; regions south have negative Galactic latitude. The point with a Galactic latitude of +90 degrees is called the north Galactic pole, and the point with a Galactic latitude of -90 degrees is called the south Galactic pole.
	is an instance of angle
	is an instance of galactic coordinate component
galactic longitude	has definition A measure of a star's position with respect to the Sun and Galactic center. Galactic longitude ranges from 0 degrees to 360 degrees. Imagine the Sun at the center of a giant clock, with the Galactic center located in the direction of six o'clock. A Galactic longitude of 0 degrees would correspond to the direction of six o'clock, a Galactic longitude of 90 degrees to the direction of three o'clock, a Galactic longitude of 180 degrees to the direction of twelve o'clock, and a Galactic longitude of 270 degrees to the direction of nine o'clock.
	is an instance of angle
	is an instance of galactic coordinate component
galactic nucleus	has definition In the innermost region of a galaxy, there is often a concentration of stars and gas, sometimes extending over thousands of light-years from the center of the galaxy.
	has definition The central region of a galaxy.
	is a part of Milky Way
galactic plane	has definition The plane that contains the disk of the Milky Way. By definition, one direction perpendicular to this plane is called "above" or "north", and the opposite direction, also perpendicular to the Galactic plane, is called "below" or "south". From Earth, due Galactic north is marked by the north Galactic pole, which lies near the bright star Arcturus, and due Galactic south is marked by the south Galactic pole, which lies in the faint constellation Sculptor.
	is a kind of plane
galactic pole	has definition Either of the two points in the sky where we look perpendicular to the disk of the Milky Way. The north Galactic pole is the Galactic pole located above the disk; the south Galactic pole is the Galactic pole located below the disk.
	has definition The poles of the galactic plane. The new system puts the galactic north pole in Coma at α(1950) = 12h49m, δ(1950) = 27°.4
	has galactic longitude 0 degrees
	is a kind of galactic coordinate
galactic rotation	has definition The revolving of a galaxy round its central nucleus even as it continues its proper motion. Such rotation, however, is not uniform but differential. One revolution of the Sun within our own Galaxy takes about 225 million years, or 1 cosmic year.
	is a kind of differential rotation
	is a kind of galaxy motion
galactic velocity component	has definition One of three components of a star's motion with respect to the center of a galaxy.
	is a kind of velocity
galactic wind	has definition A hypothetical outflow of tenuous material from a galaxy, analogous to the solar wind.
	is a part of Milky Way
Galactocentric distance	has definition A star's distance from the Galactic center. The Sun's Galactocentric distance is about 27000 light-years.
	is an instance of galactic coordinate component
	is an instance of length
galaxy	has catalog galaxy catalog
	has definition A collection of matter which usually manifests itself by the production of stars.
	has definition A huge collection of millions, billions, or trillions of stars. When referring to the Milky Way, "galaxy" is capitalized, otherwise not; thus: "Andromeda is the nearest giant galaxy to the Galaxy".
	has definition A large (108-1013 Msun), gravitationally bound aggregate of stars and interstellar matter. Galaxy formation is currently believed to have occurred around z ≈ 3-4.
	has definition A large aggregation of stars, bound together gravitationally. There are three major classifications of galaxies - spiral, elliptical, and irregular - and several subclassifications. The sun belongs to a spiral galaxy, the Milky Way galaxy.
	has definition An isolated aggregation of stars and gas, held together by their mutual gravity. A typical galaxy has about 100 billion stars, has a total mass equal to about a trillion times the mass of the sun, is about 100,000 light years in diameter, and is separated from the nearest galaxy by a distance of about 100 times its own diameter. Thus, galaxies are islands of stars in space. Our galaxy is called the Milky Way. Galaxies come in two major shapes: flattened disks with a central bulge, called spirals, and amorphous, semispherical blobs, called ellipticals. If galaxies are found bunched up next to each other, they are said to lie in groups or clusters. Clusters with a particularly large number of galaxies in them are called rich clusters. Galaxies that do not lie in such groups but rather seem to be scattered uniformly and randomly through space are called field galaxies. Some galaxies are characterized by the dominant type of radiation they emit.
	has definition Vast system of celestial objects, typically consisting of between 106 and 1012 stars, plus interstellar gas and dust. There are three basic types: spiral (further subdivided into normal spirals and spirals with a "bar" at the centre, and yet further subdivided according to the "openness" of the spiral arms), elliptical (subdivided according to ellipticity) and irregular (subdivided according to whether they are made up of Population I or Population II stars). Another not uncommon type of galaxy is a lenticular form mid-way between the spiral and the elliptical.
	has number of stars 106 to 1012
	is a kind of collection of stars
galaxy catalog	has object type galaxy or nebula (some nebulae are misidentified as galaxies)
	is a kind of catalog about star systems
galaxy cluster	has definition A conglomeration of hundreds or thousands of galaxies. The nearest large galaxy cluster is the Virgo cluster.
	has definition An aggregate of galaxies. Bautz and Morgan divide them into three morphological types: type I contains a supergiant cD galaxy; Coma is type II, type III contains no members significantly brighter than the general bright population. Virgo is type III. 21 known X-ray sources are associated with clusters of galaxies.
	has number of galaxies 102 to 103 (order of magnitude)
	is a kind of collection of galaxies
galaxy containing Cepheids	has distance determined from Cepheid period-luminosity relation
	has number of Cepheids
	is a kind of galaxy
galaxy group	has definition A small gathering of galaxies, smaller than a cluster. The Milky Way is part of the Local Group, which contains about thirty galaxies.
	has number of galaxies < 100
	is a kind of galaxy cluster
galaxy merger	has definition The formation of a galaxy from the collision of two or more separate galaxies.
	is a kind of merger
galaxy motion	is a kind of mass motion
galaxy orbital event	has participants star, galaxy
	is a kind of orbital event
galaxy peculiar velocity	has definition A deviation in the velocity of a galaxy from that expected on the basis of a uniform expansion of the universe. (See Hubble law.)
	is a kind of velocity
galaxy theory	has domain extragalactic astronomy
	is a kind of astronomy theory
Galilean satellite	has definition The largest satellites of Jupiter - Io, Europa, Ganymede, and Callisto. All are locked in synchronous rotation with Jupiter.
	has discoverer Galileo
	has discovery date 1610
	is a kind of natural satellite
	is a part of Jupiter
Galilean transformation	has definition The non-relativistic method of relating observations from one frame of reference to another.
	is a kind of coordinate transformation
Galileo Galilei	is an instance of astronomer
gallium	has image
	has ocean oxidation state III
	has ocean residence time 10000 years
	is a kind of group III element
	is a kind of metallic element
	is a kind of unclassified oceanic element
Gamma Corvi	has B-V magnitude -0.11
	has declination -17 32 31
	has right ascension 12 15 48.3
	has spectral type B8IIIpHgMn
	has synonym HR 4662
	has V magnitude 2.59
	is a part of Corvus
	is an instance of B star
	is an instance of giant
	is an instance of naked eye star
Gamma Draconis	has B-V magnitude 1.52
	has declination +51 29 20
	has right ascension 17 56 36.3
	has spectral type K5III
	has synonym HR 6705
	has V magnitude 2.23
	is a part of Draco
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
Gamma Microscopii	has B-V magnitude 0.89
	has declination -32 15 28
	has right ascension 21 1 17.4
	has spectral type G6III
	has synonym HR 8039
	has V magnitude 4.67
	is a part of Microscopium
	is an instance of G star
	is an instance of giant
	is an instance of naked eye star
Gamma Normae	has B-V magnitude 1.08
	has declination -50 09 20
	has right ascension 16 19 50.3
	has spectral type G8III
	has synonym HR 6072
	has V magnitude 4.02
	is a part of Norma
	is an instance of G star
	is an instance of giant
	is an instance of naked eye star
gamma ray	has definition An electromagnetic wave with a wavelength in the range of 10-13 to 10-10 meter, corresponding to photons with energy in the range of 104 to 107 electron volts.
	has definition Electromagnetic radiation similar to X-radiation, although of shorter wavelength, emitted spontaneously by some radioactive substances from atomic nuclei during radioactive decay.
	has definition Electromagnetic radiation with a wavelength less than about 1 Å (10-10 m); blends from the "hard" X-ray region. Photons of energy greater than about 10 keV.
	has definition Extremely short-wavelength electromagnetic energy.
	has definition Photon of very high frequency (wavelength shorter than a few tenths of an angstrom); the most energetic form of electromagnetic radiation, although there is no sharp boundary between γ-ray photon and an X-ray photon. Usually γ-ray photons come from the nucleus and X-ray photons come from the inner orbital electrons. Galactic γ-ray photons seem to originate primarily in the spiral arms.
	has definition Photons of very high frequency and very short wavelength; the most energetic and penetrating form of electromagnetic radiation.
	has definition Rays first discovered in radioactive material, and later identified as very high energy photons.
	has frequency 3 EHz or more
	has wavelength 100 pm or less
	is a kind of photon
gamma ray source	has wavelength gamma ray
	is a kind of celestial body
Gamma Sagittae	has B-V magnitude 1.57
	has declination +19 29 32
	has right ascension 19 58 45.3
	has spectral type M0III
	has synonym HR 7635
	has V magnitude 3.47
	is a part of Sagitta
	is an instance of giant
	is an instance of M star
	is an instance of naked eye star
Gamma Velorum	has absolute magnitude Mv = - 5.6
	has B-V magnitude -0.22
	has declination -47 20 12
	has definition A triple system (WC8, B1 IV, O9 I) embedded in the Gum Nebula. It is the brightest Wolf-Rayet star in the sky.
	has distance 400 pc
	has orbital period 78.5 days
	has right ascension 8 9 31.9
	has spectral type WC8+O7.5e
	has synonym HR 3207
	has V magnitude 1.78
	is a part of Vela
	is a part of Vela
	is an instance of naked eye star
	is an instance of triple star
	is an instance of WC star
gamma-ray burst	has definition Short, intense, low-energy bursts, first recorded by the Vela satellite system on 1967 July 2. Their isotropic distribution suggests an extragalactic origin, but a galactic disk origin cannot be ruled out: there is a large increase in γ-ray flux in the direction of the galactic center.
	has discovery date July 2, 1967
	has distribution isotropic with an increase towards the galactic center
	has duration 0.1 - 4 s
	has energy spectrum 0.1-1.2 MeV
	has frequency of occurrence 5 per year
	is a kind of gamma ray source
	is a part of celestial sphere
Ganymede	has definition The largest satellite of Jupiter.
	has eccentricity e = 0.0015
	has mass 1.65 × 1026 g
	has orbital period 7.155 days
	has radius 2635 km
	has synonym Jupiter III
	is a part of Jupiter
	is an instance of Galilean satellite
gas	has definition The gaseous component of a galaxy, includes nebula
	has definition A phase of matter consisting of a low density collection of particles which have no short range order
	is a kind of phase of matter
	is a part of disk
gas giant	has composition Mostly made of various light elements such as gases and simple compounds
	has definition Giant planet that has a gaseous surface.
	has synonym Jovian planet
	is a kind of planet
gas law	is a kind of thermodynamics law
gaseous element	has state gas at standard temperature and pressure
	is a kind of element
gaseous fragmentation	has definition The systematic breakup of a gas cloud into smaller and smaller subunits as the gas cools and continues to collapse. The gravitational forces continually overtake the opposing pressure gradients as long as the cloud is able to radiate freely; consequently, the Jeans mass decreases, and fragments divide into smaller subfragments. The process stops only when opacity intervenes to inhibit the cooling and radiation.
	is a kind of contraction
gaseous nebula	has catalog gaseous nebula catalog
	has definition An H II region, a supernova remnant, or a planetary nebula. H II regions have an emission-line optical spectrum, and a thermal continuous spectrum declining in intensity as the wavelength increases (from maximum in the ultraviolet) through infrared and radio. Supernova remnants have an emission-line optical spectrum and a nonthermal radio spectrum. Temperatures of planetary nebulae are much higher than those of H II regions.
	has synonym emission nebula
	is a kind of H II region
gaseous nebula catalog	has object type gaseous nebula
	is a kind of nebula catalog
gauge symmetry	has definition A property of modern theories of physics, formulated in the 1960s and confirmed by experiment. A symmetry, in general, is a property that allows a system to behave in the same way even though it has undergone some change. For instance, a snowflake has a 6-sided "rotational symmetry" - a snowflake appears identical after every 60 degree rotation. A gauge symmetry is something like a rotation, in which the amount of rotation can vary randomly from one point of space to the next. (See field theory.)
	has definition Symmetry principle underlying the quantum-mechanical description of the three nongravitational forces; the symmetry involves the invariance of a physical system under various shifts in the values of force charges, shifts that can change from place to place and from moment to moment.
	is a kind of symmetry
Gauge theory	has author Chen Ning Yang and Robert Mills (1954)
	has definition A theory that treats force in a geometrical way in terms of global and local symmetries.
	has definition A theory whose dynamics originate from a symmetry. That is, the formulae describing the theory (in particular, the Lagrangian) are unchanged under certain symmetry transformations, called "gauge" transformations. For example, the equations of classical electrodynamics are invariant under local redefinitions of the electrostatic potential. This symmetry is ultimately responsible for the conservation of electric charge. However, in quantum electrodynamics this gauge symmetry is reinterpreted as invariance under local redefinitions of the phase of the electron wave function.
	has definition Account of forces that views them as arising from broken symmetries.
	has definition In 1973 David Gross, Frank Wilczek, and David Politzer showed that these theories possess a property called asymptotic freedom, just what was needed for a theory of how quarks bind to form protons and neutrons. The new theory, dubbed quantum chromodynamics or QCD, proposed that the color of the quarks acts as the charge of the Yang-Mills interactions.
gauge theory	has gauge symmetry
Gauge theory	has name origin the term "gauge theory" is an archaic one, coming from earlier theories which were based on invariance under transformation of scale (i.e. gauge)
	has synonym Yang-Mills theories
gauge theory	is a kind of quantum field theory
Gauge theory	is a kind of unified theory
gauss	has definition Unit of magnetic flux density.
	has equivalent 10-4 tesla
	is an instance of CGS unit
	is an instance of magnetic flux density unit
Gaussian distribution	has definition A random distribution of initial conditions is often referred to as a Gaussian distribution. Also, a certain kind of bell-shaped curve is called a Gaussian.
	has definition A statistical distribution defined by the equation p = c exp(-k2x2), in which x is the statistical variable. It yields the familiar bell-shaped curve. Accidental errors of measurement and similar phenomena follow this law.
	is an instance of statistical distribution
Gaussian gravitational constant	has definition The constant defining the astronomical system of units of length (astronomical unit), mass (solar mass) and time (day), by means of Kepler's third law. The dimensions of k2 are those of Newton's constant of gravitation: L3M-1T-2.
	has symbol k
	has value 0.01720209895
	is an instance of universal constant
Gaussian year	has definition The period associated with Kepler's third law with a = 1.
	is an instance of year
gegenschein	has definition A very faint glow (about 10° across) which can occasionally be seen in a part of the sky opposite the Sun.
	has definition Faint nebulous light about 20° across near the ecliptic and opposite the Sun, best seen in September and October. Also called counterglow.
	has definition Faint oval patch of light visible from Earth only at certain times of the year, opposite the Sun. Its nature and cause are still not known. It is sometimes known as "counterglow".
	has synonym counterglow
	is a kind of backscatter
Gemini	has acronym Gem
	has boundary
	has genitive Geminorum
	has historical image
	has historical origin the twins Castor and Pollux, Greek heroes Jason led on his voyages on the Argo
	has synonym Twins
	is a part of Zodiac
	is an instance of zodiacal constellation
Gemini Telescope North	has altitude 4100: m
	has aperture 8.1 m
	has comment Coming ULE meniscus primary mirror; this northem instrument is to be optimized for IR work
	has creation date (1999)
	has focal ratio f/1.8, 16IR, 19.6
	has latitude 19° 49' N
	has location Mauna Kea, Hawaii, US
	has longitude 155° 28' W
	has owner Joint Astronomy Center
	is an instance of altazimuth telescope
	is an instance of optical telescope
	is an instance of Ritchey-Chrétien
Gemini Telescope South	has altitude 2725 m
	has aperture 8.1 m
	has comment Partners in the Gemini project are the US, UK, Canada, Chile, Brazil, and Argentina
	has creation date (2000)
	has focal ratio f/1.8, 6
	has latitude 30° 21' S
	has location Cerro Pachon, Chile
	has longitude 70° 49' W
	has owner Cerro Tololo Inter-American Obs.
	is an instance of altazimuth telescope
	is an instance of optical telescope
	is an instance of Ritchey-Chrétien
Geminid	has duration 3 days
	has parent object Asteroid Phaethon
	has radiant Gemini
	has rate 90 per hour
	has start time 13 December
	is an instance of meteor shower
general precession	has definition The sum of the lunisolar and the planetary precession. It causes the ecliptic longitude to increase at a constant rate but has no effect on ecliptic latitude.
	has rate 50".27 per year
	is an instance of precession
general relativity	has author Einstein (1915)
	has competing theory twistor theory
	has definition Gravitation is a curvature in four-dimensional space-time rather than as a force existing between two masses.
	has implication four-dimensional structure of space-time
	has phenomena gravity
	has subset special relativity
	has synonym Einstein's theory of gravity
	is an instance of relativity theory
geocentric coordinate	has component geocentric coordinate component
	has coordinate origin Earth
	has definition The latitude and longitude of a point on the Earth's surface relative to the center of the Earth; also celestial coordinates given with respect to the center of the Earth.
	has definition The longitude and latitude of a point on the Earth relative to the geoid. These coordinates are influenced by local gravity anomalies.
	has height
	has terrestrial latitude
	has terrestrial longitude
	is a kind of coordinate
geocentric coordinate component	is a component of geocentric coordinate
	is a kind of coordinate component
geocentric cosmology	has definition A model of the universe in which the earth is centrally located, and the Sun, planets, and stars revolve around the Earth.
	has definition School of ancient theories that depicted the earth as standing, immobile, at the center of the universe.
	is a kind of outdated belief
geocorona	has definition The outermost part of Earth's atmosphere, a hydrogen halo extending out to perhaps 15 Earth radii, which emits Lyman-α radiation when it is bombarded by sunlight.
	is a part of atmosphere
geodesy	has definition Measurement and study of the Earth's size and shape.
	is a kind of geology
geodetic coordinate	has definition The latitude and longitude of a point on the Earth's surface determined from the geodetic vertical (normal to the specified spheroid). (See zenith; latitude, terrestrial; longitude, terrestrial.)
	is a kind of coordinate
geodetic precession	has definition A small, relativistic, direct motion of the equinox along the ecliptic.
	has rate 1".915 per century
	is an instance of precession
geological era	is a kind of era
geology	has definition Scientific study of the dynamics and history of the earth, as evidenced in its rocks, chemicals, and fossils.
	is a kind of science
geometrical object	has dimensions
	is a kind of mathematical concept
geophysical satellite	is a kind of artificial satellite
George Ellery Hale Telescope	has altitude 1706 m
	has aperture 5.08 m
	has creation date 1948
	has focal ratio f/3.3. 16, 30
	has latitude 33° 21' N
	has location Palomar Mountain, Calif., US
	has longitude 116° 52' W
	has mirror maker J.A. Anderson
	has mirror type ribbed Corning Pyrex
	has mounting Horseshoe yoke mount
	has mounting manufacturer Westinghouse
	has operator California Institute of Technology
	has owner Palomar Observatory
	has synonym 200 inch
	is an instance of Cassegrain
	is an instance of Horseshoe equatorial telescope
	is an instance of optical telescope
GEOS 10	is an instance of GEOS satellite
GEOS 11	is an instance of GEOS satellite
GEOS 8	is an instance of GEOS satellite
GEOS satellite	is a kind of geosynchronous satellite
	is a kind of NOAA satellite
	is an acronym for Geostationary Operational Environmental Satellite
geosynchronous satellite	has constant longitude
	has definition an artificial satellite which orbits Earth every 24 hours
	has location above the same position on the Earth
	has orbital inclination approximately zero degrees
	has orbital period 24 hours (one day)
	is a kind of artificial satellite
	is a part of Earth
	orbits Earth
German equatorial telescope	has mounting German equatorial
	is a kind of equatorial telescope
germanium	has image
	has ocean oxidation state IV
	has ocean residence time 20000 years
	is a kind of group IV element
	is a kind of metallic metalloid
	is a kind of recycled oceanic element
	is a kind of siderophile element
giant	has definition 1. A star that has evolved off the main sequence and is roughly a hundred times as luminous as the Sun. Giants can be of any color, but yellow, orange, and red giants are the most common. 2. A planet much more massive than Earth. The solar system has four giant planets, all far from the Sun: Jupiter, Saturn, Uranus, and Neptune.
	has definition High-luminosity star that lies above the main sequence on the Hertzsprung-Russell diagram.
	has luminosity class III
	is a kind of star
giant elliptical galaxy	has definition Massive elliptial galaxy which is too far for individual stars to be resolved.
	has mass 1013 Msun (most massive galaxies known)
	is a kind of elliptical galaxy
giga	has symbol G
	has value 109
	is an instance of unit prefix
GIS	has definition Gas Imaging Spectrometer (ASCA X-ray satellite).
	is a kind of high energy detector
global inertial frame	has definition A coordinate system or frame of reference anchored with respect to the overall distribution of matter in the universe.
	is a kind of nonaccelerating reference frame
	is a kind of nonrotating reference frame
globular cluster	has age oldest stellar formation in the Galaxy
	has catalog globular cluster catalog
	has definition A tightly packed, symmetrical group of thousands of very old (pure Population II) stars. The stellar density is so great in the center that the nucleus is usually unresolved. The stars within a globular cluster orbit each other because of their mutual gravity.
	has diameter about 100 light-years
	has location most are in the halo some are members of the thick disk
	has mass 104 to 106 Msun
	has number of stars 105 to 106
	has orbit elongated, around the galactic center
	has spectra low abundances of heavy elements
	has velocity very high
	is a kind of star cluster
	is a part of halo
globular cluster catalog	has object type globular cluster
	is a kind of catalog about star systems
glueball	has definition Theoretical particles made exclusively of gluons. Tentative evidence of the existence of glueballs had been found in accelerator experiments by the mid-1980s.
	is a kind of hypothetical particle
gluon	carries the force strong force
	has color charge
	has definition Gluons are the massless gauge bosons of QCD which mediate the strong color force between quarks. Because of the non-Abelian structure of the theory, gluons can interact with themselves, and may form particles consisting of gluons bound together. The existence of these "glueballs" has yet to be confirmed.
	has definition Quanta that carry the strong nuclear force. Like photons, vector bosons, and gravitons - the carriers respectively of electromagnetism, the weak force, and gravitation - gluons are massless bosons. Consequently, for simplicity's sake, some physicists lump together all the force-carrying quanta under the term "gluons".
	has definition Smallest bundle of the strong force field; messenger particle of the strong force.
	has definition The force-carrying particles associated with the strong interactions, the forces which bind quarks inside of protons and neutrons. For more details, see Yang-Mills theories.
	has definition The hypothetical particle that carries the force between quarks.
	is a kind of carrier boson
	is a kind of massless particle
	is a kind of parton
GMS	has launch date 14 Jul 1977
	has launch location Kenedy Space Center
	has launch vehicle Delta rocket
	has mass 315 kg
	is an instance of GMS satellite
GMS satellite	has definition Geostationary Meteorological Satellite
	has specification
	is a kind of geosynchronous satellite
	is a kind of NASDA satellite
GMS-2	has launch date 11 Aug 1981
	has launch location Tanegashima Space Center, Kagoshima, Japan
	has launch vehicle N-II rocket
	has mass 296 kg
	is an instance of GMS satellite
GMS-3	has launch date 3 Aug 1984
	has launch location Tanegashima Space Center, Kagoshima, Japan
	has launch vehicle N-II rocket
	has mass 303 kg
	is an instance of GMS satellite
GMS-4	has attitude control spin stabilized
	has constant longitude 140 deg east
	has dimension 2.146 m diameter cylinder, height 0.3451 m
	has launch date 6 Sept 1989
	has launch location Tanegashima Space Center, Kagoshima, Japan
	has launch vehicle H-I rocket
	has mass 325 kg
	is an instance of GMS satellite
GMS-5	has attitude control spin stabilized
	has constant longitude 140 deg east
	has dimension 2.146 m diameter cylinder, height 0.3451 m
	has image
	has launch date early 1995
	has launch location Tanegashima Space Center, Kagoshima, Japan
	has launch vehicle H-II rocket
	has mass 344 kg
	is an instance of GMS satellite
Goddard Space Flight Center	has acronym GSFC
	is an instance of space science institution
GOES-L	has creator NASA
	has image
	has launch date 3 May 2000
	has launch vehicle Lockheed Martin Atlas IIA rocket
	is an instance of GEOS satellite
Golay cell	has definition A gas bulb used to detect infrared radiation.
	is a kind of detector
gold	has image
	has ocean oxidation state I
	is a kind of siderophile element
	is a kind of supernova produced element
	is a kind of transition metal
	is a kind of unclassified oceanic element
Goldstone boson	has definition A massless spin-0 particle which arises whenever a (continuous) global symmetry is spontaneously broken.
	has spin 0
	is a kind of boson
	is a kind of hypothetical particle
Gould Belt	has definition The local system of stars and gas within about 300 pc of the Sun in which the greatest concentration of naked-eye O and B stars occurs.
	has distance from Sun 300 pc
	has inclination 10° to 20° to the galactic plane
	is a part of Orion arm
GPS satellite	is a kind of navigation satellite
Gran Telescopio Canarias	has acronym GTC
	has altitude 2400 m
	has aperture 10 m
	has comment Design similar to that of the Keck instruments; funded by Spain with international partners
	has creation date 2003
	has focal ratio f/1.75. 15, 25
	has latitude 28° 45' N
	has location La Palma, Canary Islands
	has longitude 17°54' W
	has owner Obs. del Roque de los Muchachos
	is an instance of altazimuth telescope
	is an instance of optical telescope
	is an instance of Ritchey-Chrétien
	is an instance of segmented mirror telescope
grand unified theory	has acronym GUT
	has definition A speculative class of theories of particle interactions, first developed in 1974, which attempt to describe electromagnetism, the weak interactions, and the strong interactions in a fully unified theory. Of the known forces, only gravitation is omitted.
	has definition An attempt to produce a unification of all the forces of nature. While some success was made in unifying the gluon force between quarks with the electroweak force, problems always arose when gravity was included. Grand unification eventually gave way to superstring theory.
	has definition Class of theories that merge all three nongravitational forces into a single theoretical framework.
	has definition Class of theories that purport to reveal identities linking the strong and electroweak forces. The differences between these forces in nature today is attributed to the breaking of symmetrical relationships among force-carrying particles as the very early universe expanded and cooled.
	has definition Theory in physics that attempt to explain the forces of nature as manifestations of a single underlying force.
	has synonym grand unification
	is a kind of unified theory
granule	has definition Convective cell in the solar photosphere. A granule represents a temperature roughly 300° higher than the surrounding dark areas. At any one time, granules cover about one-third of the solar photosphere.
	has definition The mottled appearance of the solar photosphere, caused by gases rising from the interior of the Sun.
	has diameter 1000 km in diameter
	has lifetime 5 minutes
	is a part of photosphere
gravitational collapse	has definition The sudden collapse of a massive star when the radiation pressure outward is no longer sufficient to balance the gravitational pressure inward. In gravitational collapse there is a sudden, catastrophic release of great quantities of gravitational potential energy, and this release has been postulated as the cause of supernovae, neutron stars, and black holes.
	is a kind of collapse
gravitational contraction	is a kind of energy source
gravitational lens	has definition A galaxy that intervenes between us and a distant astronomical object and that gravitationally deflects the light from that distant object. (Light, like matter, is attracted by gravity.) Gravitational lenses can focus, distort, and split light beams in the same way that ordinary glass lenses do.
	is a kind of galaxy
gravitational lensing	has definition Deflection of electromagnetic radiation from a distant background source by a strong gravitational field associated with a foreground source resulting in more than one image of the original source. Many double-quasars are produced by this phenomenon.
	has definition Gravitational effect that bends a ray of light. Such an effect was predicted within the general theory of relativity, although previously considered impossible.
	has definition The apparent path of a photon is altered from a straight line by the gravitational field of the Sun. The path is deflected radially away from the Sun by up to 1".75 at the Sun's limb. Correction for this effect, which is independent of wavelength, is included in the reduction from mean place to apparent place.
	has definition The bending of light caused by the gravity of an object lying between us and the light source. This may cause the light source to look brighter than it normally does.
	has definition The bending of the beam of light due to gravity. It is observable when the light from a star or planet passes a massive object such as the Sun.
	has definition The effect of matter in curved spacetime, which tends to focus any beam of radiation from a distant source. In effect, the spacetime curvature is a lens of great focal length. At z ≈ 1, the angular size of an object starts increasing with distance.
	has synonym deflection of light
	is a kind of radiation direction modification
gravitational mass	has definition That property of matter which makes it create a gravitational field and attract other particles (cf. inertial mass; equivalence principle).
	is an instance of mass
gravitational potential energy	has definition Energy that a body can acquire by falling through a gravitational field and that decreases as the kinetic energy increases. There is no general reference level (analogous to the state of rest of a body in defining kinetic energy), and so we customarily define the change in gravitational potential energy as the negative of the work done by the gravitational forces during the bodys change of position.
	has definition When we lift a weight from the floor to a tabletop, we clearly put energy into it. The energy is not lost, however, because we can retrieve it by allowing the weight to fall back to the floor. While the weight is on the table, we say that the energy is stored as gravitational potential energy. The energy is stored in the gravitational field.
	is a kind of potential energy
gravitational radius	has definition The radius which an object should have in order that light emitted from its surface just ceases to escape from its surface.
	is an instance of radius
gravitational redshift	has definition Displacement of spectral lines toward longer wavelengths due to the effects of gravity.
	has definition Light is emitted at a lower frequency and longer (or redder) wavelength in a gravitational field than in the absence of a gravitational field.
	has definition The rate at which a clock keeps time when it is in a gravitational field is slower than the rate at which it will keep time in the absence of a gravitational field. (The gravitational redshift was experimentally verified by Pound and Rebka in 1960.) The amount of redshift is directly proportional to the mass of the emitting body and inversely proportional to its radius.
	has example Object Gravitational Redshift Earth 10-9 white dwarf 10-4 black hole large (proportional to mass divided by radius)
	has synonym Einstein effect
	is a kind of wavelength shift
gravitino	has definition Hypothetical force-carrying particles predicted by supersymmetry theories. The gravitino's spin would be 1/2. Its mass is unknown.
	is a kind of hypothetical particle
graviton	carries the force gravity
	has definition A hypothetical elementary particle associated with the gravitational interaction. It is a stable particle with zero rest mass, zero charge, and a spin of ± 2, and travels with the speed of light.
	has definition A massless spin-2 particle which is the hypothetical quantum of the gravitational field. It mediates the force of gravity in a similar way to that in which the spin-1 gauge bosons (i.e. the photon, W±, Z0, and gluons) mediate the other forces.
	has definition A quantum of gravitational radiation.
	has definition Smallest bundle of the gravitational force field; messenger particle for the gravitational force.
	has definition The hypothetical quantum particle of the gravitational field. It could also be thought of as a quantized element of space-time curvature.
	has definition The quanta thought to convey gravitational force; analogous to the photons, gluons, and intermediate vector bosons of electromagnetism and the strong and weak nuclear forces. Predicted by quantum theory of gravity, gravitons have not yet been detected.
	has spin 2
	is a kind of carrier boson
	is a kind of hypothetical particle
	is a kind of massless particle
	is a kind of neutral particle
gravity	has carrier boson graviton
	has definition As described first by Isaac Newton, gravity is a force that exists between bodies of any mass whatever (from particles to stars) in proportion to the product of their masses, and in inverse proportion to the square of the distance between them. The weakest of the four natural forces (the other three being the electromagnetic and the two nuclear interactive forces), its real nature is still not fully understood. Einstein's General Theory of Relativity presented another viewpoint.
	has definition Fundamental force of nature, generated by all particles that possess mass. Interpreted by means of Newtonian mechanics or by the general theory of relativity.
	has definition In Aristotelian physics, an innate tendency of the elements earth and water to fall. In Newtonian physics, the universal, mutual, attraction of all massive objects for one another; its force is directly proportional to the mass of each object, and decreases by the square of the distance separating the objects involved. In Einstein's general relativity, gravity is viewed as a consequence of the curvature of space induced by the presence of a massive object. In quantum mechanics the gravitational field is said to be conveyed by quanta called gravitons.
	has definition One of the four fundamental forces of nature, and the one most different from the other three.
	has definition The mutual attraction between any two masses, as was first described accurately by Newton. Gravity appears strong because it has infinite range and it is always attractive (except for a false vacuum), but on a subatomic level gravity is the weakest of the known interactions; the gravitational force between a proton and an electron is 2 × 1039 times weaker than the electrical attraction.
	has definition The universal ability of all material objects to attract each other; F = Gm1m2 / r2.
	has definition The weakest of the four fundamental forces of nature, the gravitational force between any two masses is proportional to the product of the masses and varies inversely as the square of the distance between them. The other three fundamental forces are the electromagnetic force and two kinds of nuclear forces. (See electromagnetic force; nuclear forces.)
	has definition The weakest of the four fundamental forces of nature. Described by Newton's universal theory of gravity, and subsequently by Einstein's general relativity.
	has range infinite
	has strength (relative to electromagnetism)
	is a kind of fundamental force
gravity law	has domain gravity
	is a kind of law
gravity wave telescope	is a kind of telescope
gray	has base unit m2·s-2
	has symbol Gy
	has unit J·kg-1
	is an instance of named derived SI unit
	is an instance of radioactivity unit
	represents absorbed dose, specific energy (imparted), kerma
grazing-incidence telescope	has acronym XRT
	has definition A telescope used in X-ray and gamma-ray astronomy. It focuses these rays by making use of the fact that they behave like light rays if they strike surfaces at a shallow enough angle.
	has number of concentric surfaces
	is a kind of X-ray space telescope
great circle	has definition A circle on the surface sphere whose diameter equal to the diameter of the sphere.
	is a kind of circle
Great Rift	has definition A split in the Milky Way between Cygnus and Sagittarius caused by a succession of large, overlapping dark clouds in the equatorial plane of the Galaxy.
	has distance from Sun 100 pc
	is a part of Orion arm
Great Wall	has definition A sheet of galaxies which stretches more than 500 million light-years across the sky.
	is a kind of collection of galaxies
greatest elongation	has definition The instants when the geocentric angular distances of Mercury or Venus are at a maximum from the Sun.
	has elongation varies
	is a kind of planetary elongation event
	is an instance of planetary elongation
green	is a kind of optical
Gregorian	has definition A class of reflecting telescope which uses a concave secondary mirror placed after the prime focus is reached instead of a convex secondary placed before the prime focus.
	has definition Telescope devised - but never constructed - by James Gregory, in which an auxiliary concave mirror reflects the magnified image, the right way up, through a hole in the centre of the main objective mirror, i.e., through the end of the telescope itself. The Cassegrain telescope is similar but produces an inverted image.
	has secondary mirror shape concave
	is a kind of reflector
grism	has definition This is a right-angled glass prism with a transmission diffraction grating deposited on the hypotenuse surface. The spectrum produced by the grating is deflected by the prism to remain on the optical axis and the apex angle of the prism is chosen to get a certain wavelength in the center of the detector. Grisms can be placed in a filter wheel.
	is a kind of diffraction grating
Groombridge 1830	has definition A famous halo star whose proper motion, discovered in 1841, was then the largest known, displacing that of 61 Cygni.
	has distance 28 light-years
	is a part of Ursa Major
	is an instance of high proper motion star
Grosser Refraktor	has altitude 241 m
	has aperture 0.67 m
	has creation date 1880
	has focal ratio f/15.7
	has latitude 48° 14' N
	has lens maker Grubb
	has location Vienna, Austria
	has longitude 16° 20' E
	has mounting manufacturer Grubb
	has owner Astronomisches Inst., Univ. Obs.
	is an instance of German equatorial telescope
	is an instance of refractor
Grosser Refraktor^2	has altitude 41 m
	has aperture 0.68 m
	has creation date 1896
	has focal ratio f/30.9
	has latitude 52° 29' N
	has lens maker C.A. Steinheil
	has location Alt Treptow, Berlin, Germany
	has longitude 13° 29'E
	has mounting manufacturer Hoppe-Berlin
	has owner Arehenhold-Sternwarte
	is an instance of German equatorial telescope
	is an instance of refractor
ground state	has definition The state in which all electrons are in the lowest possible energy states.
	is a kind of energy
group III element	has group 13
	is a kind of column grouped element
group IV element	has group 14
	is a kind of column grouped element
group V element	has group 15
	has synonym pnictogen
	is a kind of column grouped element
group VI element	has group 16
	has synonym chalcogen
	is a kind of column grouped element
Grus	has acronym Gru
	has boundary
	has genitive Gruis
	has historical image
	has historical origin the crane or Phoenicopterus (Flamingo), in the past used to be part of Piscis Austrinus.
	has synonym Crane
	is a part of celestial sphere
	is an instance of constellation named by Bayer
gyrofrequency	has definition The frequency with which an electron or other charged particle executes spiral gyrations in moving across a magnetic field.
	is a kind of frequency
H alpha	has upper energy level 3
	has wavelength 6563 Å
	is an instance of Balmer line
	is an instance of Fraunhofer line
	is an instance of spectral line
h and Chi Persei	has definition A double stellar association. It contains many young O and B stars and also many M supergiants.
	has distance 2 kpc
	has synonym double cluster in Perseus
	has synonym Perseus OB1
	is a part of Perseus
	is a part of Perseus arm
	is an instance of naked eye object
	is an instance of OB association
H and K emission line star	has definition Late objects (F4 to M), which exhibit emission features in their Ca II HK lines.
	has emission line Ca II HK lines
	is a kind of emission line star
	is a kind of late star
H beta	has upper energy level 4
	has wavelength 4861 Å
	is an instance of Balmer line
	is an instance of Fraunhofer line
	is an instance of spectral line
H delta	has upper energy level 6
	has wavelength 4101 Å
	is an instance of Balmer line
	is an instance of spectral line
H gamma	has upper energy level 5
	has wavelength 4342 Å
	is an instance of Balmer line
	is an instance of spectral line
H II condensation	has definition A high-density H II region.
	is a kind of H II region
H II region	has composition ionized hydrogen
	has definition An area of ionized hydrogen. Most H II regions are red and arise from hot blue O and B stars, whose ultraviolet light can ionize all the hydrogen for dozens or even hundreds of light-years in every direction. The most famous H II region is the Orion Nebula.
	has definition Hydrogen gets ionized by hot O and B stars in H II regions. The most famous H II region is the Orion Nebula.
	has definition Region of ionized hydrogen in interstellar space. H II regions occur near stars with high luminosities and high surface temperatures. The kinetic temperature of H II regions is about 10,000-20,000 K, and the density is about 10 atoms per cm3. Ionized hydrogen, of course, having no electron, does not produce spectral lines; however, occasionally a free electron will be captured by a free proton and the resulting radiation can be studied optically (see also radio recombination lines).
	is a kind of nebula
H magnitude	has band 1.6 microns
	has definition The magnitude derived from observations at 1.6 microns.
	is an instance of infrared magnitude
h-line	has definition Singly ionized magnesium resonance line.
	has species Mg II
	has wavelength 2803 Å
	is a kind of absorption line
Hades	has definition An unofficial name for Jupiter IX, the outermost satellite of Jupiter.
	has discoverer Nicholson
	has discovery date 1914
	has eccentricity e = 0.28
	has inclination i = 156°
	has orbital period P = 758 days retrograde
	has synonym Jupiter IX
	is a part of Jupiter
	is an instance of natural satellite
hadron	has definition High mass elementary particles that are influenced by the strong nuclear force.
	is a kind of elementary particle
hadron era	has definition The Big Bang era during which quantum and general-relativistic effects are expected to modify each other in an unknown way.
	has definition The Big Bang era when the Universe was matter-dominated, containing many hadrons in equilibrium with the radiation field and when kT ≈ mπ. The hadron era ended when the characteristic photon energy fell below the rest mass of a pion or π-meson (270 electron masses), and very few hadrons remained (about one hadron for every 108 photons).
	has density ρ = 1093 g cm-3
	has duration 10-5 s
	has start time 10-43 s after Big Bang
	has synonym hadron barrier
	is a kind of Big Bang era
	is followed by lepton era
	is preceded by Planck era
hafnium	has image
	has ocean oxidation state IV
	is a kind of transition metal
	is a kind of unclassified oceanic element
Hale	has associate Shapley
	has birth date 29 June 1868
	has career 1886-1996 : Harvard & private observatory 1887-1904 : Yerkes/Chicago 1904-1923 : Mt. Wilson 1923-1938 : honorary director & private observatory
	has death date 21 February 1938
	has degree 1890 : BSc. MIT 12 honorary PhDs
	has image
	has name George Ellery Hale
	has name George Ellery Hale
	has orbituary Adams, W.S. : 1938, ApJ 87, 369. Babcock, H.D. : 1938, PASP 50, 156. Dunham, T. : 1938, MNRAS 99, 322.
	is an instance of 19th century scientist
	is an instance of astronomer
half-life	has definition Time it takes for the number of particles to halve. For a radioactive substance, the length of time required for half the atoms to disintegrate.
	has symbol τ1/2
	is a kind of time
	see also mean life
half-power beamwidth	has acronym HPBW
	has definition The angle across the main lobe of an antenna pattern between the two directions where the sensitivity of the antenna is half the value at the center of the lobe. This is the nominal resolving power of the antenna system.
	is a kind of angle
Halley's comet	has definition Probably the best known of all comets. Its orbit was computed by Edmund Halley in 1704, at which time he predicted that the bright comet of 1682 would return in 1758 (Halley died in 1742, before he could see his prediction verified). Records of Halley's comet (a = 17.8 AU, e = 0.967, i = 162°.3, P = 76.2 yr perihelion distance 0.587 AU) have been traced back to 240 B.C. Last appearance 1910, next appearance 1986.
	is a part of our solar system
	is an instance of comet
halo	has definition A spherical aggregation of stars, globular star clusters, and thin gas clouds, centered on the nucleus of the galaxy and extending beyond the known extremities of the galactic disk.
	has definition the galactic halo, however, describes the spherical collection of stars forming a surrounding "shell" for our otherwise compact, discoid Galaxy.
	has definition The somewhat round population of old, metal-poor stars in the Milky Way. Also, the huge entity that surrounds the disk and contains most of the Galaxy's dark matter. To distinguish between the two, astronomers call the former the stellar halo and the latter the dark halo. Most of the stellar halo lies closer to the Galactic center than the Sun, while most of the dark halo lies farther from the Galactic center than the Sun.
	is a part of Milky Way
halogen	has group 17
	has synonym group VII element
	is a kind of column grouped element
	is a kind of nonmetallic element
hard gamma ray	is a kind of gamma ray
hard X-ray	is a kind of X-ray
Harlan J. Smith Telescope	has altitude 2075 m
	has aperture 2.72 m
	has creation date 1969
	has focal ratio f/3.9, 8.8, 18
	has latitude 30° 4d N
	has location Mount Locke, Texas, US
	has longitude 104° 01' W
	has mirror maker Davidson Optronics
	has mirror type Fused-silica
	has mounting Cross-axis equatorial
	has mounting manufacturer Westinghouse
	has owner McDonald Observatory
	has synonym 107 inch
	is an instance of Cross-axis equatorial telescope
	is an instance of optical telescope
	is an instance of Ritchey-Chrétien
harmonic motion	has amplitude
	has definition A motion that repeats itself in equal intervals of time. An oscillating particle in harmonic motion is a harmonic oscillator.
	has period
	has synonym periodic motion
	is a kind of motion
harmonic overtone	has definition Any integral multiple of the fundamental frequency
	is a kind of frequency
Haro galaxy	has definition Blue object whose spectra show sharp emission lines.
	is a kind of emission line galaxy
Hartree energy	has equation
	has symbol Eh
	has uncertainty 0.00000034 × 10-18 J
	has value 4.35974381 × 10-18 J
	is an instance of atomic constant
	is an instance of energy
Harvard College Observatory	has owner Harvard
	is an instance of observatory
hassium	is a kind of transactinide
HD 141569	has distance 320 light years
	has image
	is a part of Libra
	is an instance of star
He II Balmer alpha	has wavelength 1640 Å
	is an instance of ionized helium Balmer line
He II Lyman alpha	has wavelength 303.78 Å
	is an instance of ionized helium Lyman line
	is an instance of resonance line
He II Paschen alpha	has wavelength 4686 Å
	is an instance of ionized helium Paschen line
He2-104	has image
	is an instance of symbiotic star
head-tail galaxy	has definition A class of relatively weak radio sources associated with clusters of galaxies and characterized by a high-brightness "head" close to the optical galaxy and a long low-brightness "tail".
	is a kind of radio galaxy
HEAO	has definition High-Energy Astronomical Observatory.
	is an instance of X-ray space telescope
heavy quark	is a kind of quark
heavy-metal star	has definition A class of peculiar giant that includes the Ba II stars and the S stars.
	is a kind of giant
hecto	has symbol h
	has value 102
	is an instance of unit prefix
height	has definition Elevation above ground or distance upwards from a given level (especially sea level) to a fixed point. (See altitude.)
	is an instance of geocentric coordinate component
	is an instance of length
Hektor	has albedo 0.28
	has asteroid number 624
	has definition Largest and brightest Trojan asteroid.
	has diameter 100 km
	has obliquity large
	has rotation period 6.9225 hours
	has shape elongated
	has visual magnitude +14.5 (at mean opposition)
	is a part of Trojan asteroid
	is an instance of Trojan asteroid
heliocentric cosmology	has definition School of models in which the sun was portrayed as standing at the center of the universe.
	is a kind of outdated belief
heliograph	has definition Device for recording the positions of sunspots.
	is a kind of integrating detector
helion mass	applies to particle helion
	has symbol mh
	has uncertainty 0.00000039 × 10-27 kg
	has value 5.00641174 × 10-27 kg
	is an instance of particle mass
helium	has abundance 0.008 p.p.m. in Earth's crust
	has abundance 4 × 10-6 p.p.m. in seawater
	has abundance 5.2 p.p.m. by volume in Earth's atmosphere
	has abundance 6.31 × 1010 in Sun relative to H = 1 × 1012
	has atomic emission line 1083.025 nm for He I
	has atomic emission line 1868.534 nm for He I
	has atomic emission line 2058.130 nm for He I
	has atomic emission line 388.865 nm for He I
	has atomic emission line 587.562 nm for He I
	has atomic emission line 1083.034 nm for He I (strong)
	has atomic number 2
	has atomic radii 128 pm
	has biological role none
	has boiling point 4.216 K
	has chief source natural gas which may contain up to 7% helium
	has critical pressure 229 kPa
	has critical temperature 5.25 K
	has crystal cell dimension a = 353.1, c = 569.3 pm for α-He at 1.15 K, 6.69 MPa
	has crystal cell dimension a = 411 pm for γ-He at 1.73 K, 2.94 MPa
	has crystal cell dimension a = 424.0 pm for β-He at 16K, 127 MPa
	has crystal type b.c.c. for γ-He at 1.73 K, 2.94 MPa
	has crystal type f.c.c. for β-He at 16K, 127 MPa
	has crystal type h.c.p. for α-He at 1.15 K, 6.69 MPa
	has daily dietary intake very low
	has definition
	has definition Colourless, odorless gas obtained mainly from gas wells. Element which, after hydrogen, is the second lightest and second most abundant in the Universe. Its atom comprises two protons and two electrons. The nucleus of helium 4 is sometimes called an alpha particle. Helium is the product of the nuclear fusion of hydrogen in most stars, but this does not explain the overall helium abundance. Most of it was produced by the big bang, with main-sequence stars making an additional contribution.
	has density 0.1785 kg m-3 for gas at 273 K
	has density 124.8 kg m-3 for liquid at 4.216 K boiling point
	has discoverer Norman Lockyer and Edward Frankland
	has discovery date 1868
	has discovery location England
	has electron affinity 0.0 kJ mol-1 from to -
	has electron configuration 1s2 = [He] in ground state
	has hazard harmless but could asphyxiate if it excludes oxygen from the lungs
	has heat capacity 20.786 J K-1 mol-1 for gas at constant pressure 0.1 MPa at 298.15 K
	has heat of fusion 0.021 kJ mol-1
	has heat of vaporization 0.082 kJ mol-1
	has image
	has isotope mass range 3 to 8 except 7
	has lethal intake non-toxic
	has level in humans traces
	has longest lived isotope helium 4
	has mass absorption coefficient 0.207 cm2 g-1 for MoKα X-ray diffraction
	has mass absorption coefficient 0.383 cm2 g-1 for CuKα X-ray diffraction
	has mass magnetic susceptibility -5.9 × 10-9 kg-1 m3 for gas
	has mass of element in person very small for a 70 kg average person
	has melting point 0.95 K under pressure
	has mineral present in some minerals
	has molar volume 32.07 cm3 at 4 K
	has name origin helios = sun from Greek
	has neutron scattering length 0.326 × 10-12 cm
	has number of isotopes 5 including nuclear isomers
	has number of protons 2
	has ocean oxidation state 0
	has pronunciation heel-iuhm
	has registry number 7440-59-7 for Chemical Abstracts System database
	has relative atomic mass 4.005602 in units of 12C = 12.000
	has reserves 3.7 × 109 tonnes in Earth's atmosphere
	has space group Fm3m for β-He at 16K, 127 MPa
	has space group Im3m for γ-He at 1.73 K, 2.94 MPa
	has space group P63/mmc for α-He at 1.15 K, 6.69 MPa
	has specimen small pressurized canisters. Safe.
	has stable isotope helium 3, helium 4
	has symbol He
has synthesis mechanism
has term symbol 1S0 in ground state
has thermal conductivity 0.152 W m-1 K-1 at 300 K
has thermal neutron capture cross section 0.007 barns
has toxic intake non-toxic
has uses deep-sea diving, weather baloons, low temperature research
has van der Waals radii 120 pm
has world production 4500 tonnes year-1
is a kind of inert gas
is a kind of light element
is a kind of unclassified oceanic element
reacts with nothing
helium 3	has atomic mass 3.01602931
	has magnetogyric ratio -20.378 × 107 rad T-1 s-1
	has natural abundance 0.000137 % stable isotope
	has NMR frequency 76.178 MHz where 1H = 100 MHz; 2.3488 T
	has NMR receptivity 0.00326 where 13C = 1.00
	has nuclear magnetic moment μ = -2.127624
	has nuclear spin I = 1/2
	has number of neutrons 1
	has number of nucleons 3
	has relative NMR sensitivity 0.44 where 1H = 1.00
	has symbol 3He
	has uses Nuclear Magnetic Resonance, tracer
	is an instance of helium
helium 4	has atomic mass 4.00260324
	has natural abundance 99.999863 %
	has nuclear magnetic moment μ = 0
	has nuclear spin I = 0+
	has number of neutrons 2
	has number of nucleons 4
	has symbol 4He
	is an instance of helium
helium 6	has atomic mass 6.018886
	has decay mode β- (3.5010 Mev) 100 %
	has decay mode γ
	has half life 0.807 seconds
	has nuclear spin I = 0+
	has number of neutrons 4
	has number of nucleons 6
	has symbol 6He
	is an instance of helium
helium 8	has atomic mass 8.03392
	has decay mode β- (14 Mev)
	has decay mode β- n
	has decay mode γ
	has half life 0.119 seconds
	has nuclear spin I = 0+
	has number of neutrons 6
	has number of nucleons 8
	has symbol 8He
	is an instance of helium
helium burning	has definition The stage when a star fuses helium into carbon and oxygen. All stars born with more than half a solar mass eventually burn helium.
	has duration 5 × 105 years
	has next higher temperature reaction carbon burning
	has optimum density 700 g/cm3
	has optimum temperature 2 × 108 K
	has part product carbon
	has product carbon, oxygen
	has reactant helium
	is a kind of exothermic fusion process
	requires minimum mass at star birth 0.5 solar masses
Helium discontinuity	has species helium (He I)
	is a kind of absorption edge
helium flash	has definition The onset of runaway helium burning under degenerate conditions. The helium flash occurs in the hydrogen-exhausted core of a star in the red-giant phase of evolution. When gravitational pressure has brought the degenerate core to a temperature of about 108 K, the helium nuclei can start to undergo thermonuclear reactions. Once the helium burning has started, the temperature builds up rapidly (without a cooling, stabilizing expansion), and the extreme sensitivity of the nuclear reaction rate to temperature causes the helium-burning process to accelerate. This in turn raises the temperature, which further accelerates the helium burning, until a point is reached where the thermal pressure expands the core and thus removes the degeneracy and limits the flash. The helium flash can only occur when the helium core is less than the 1.4 Msun Chandrasekhar mass limit and thus it is restricted to low-mass stars.
	has minimum temperature 108 K
	is a kind of helium burning
helium problem	has definition Poses the question: what physical process caused the current abundance of helium in the Universe?
	is an instance of problem
helium shell flash	has definition It has been shown that helium shell burning outside a degenerate core is unstable; the helium-burning shell does not generate energy at a constant rate but instead produces energy primarily during short flashes. During a flash, the region just outside the helium-burning shell becomes unstable to convection. The resultant mixing probably leads to the s-process as well as to the upward movement of carbon produced by helium burning.
	is a kind of helium burning
helium temperature scale	has approval date 1958
	has definition The vapour pressure of helium 4 is used as an indication of temperature in the region 1 to 5.2 K.
	is an instance of temperature unit
helium variable star	has definition Bp star in which the strength of the helium lines varies periodically. At the extreme phases the objects appear as helium-rich, whereas at other phases He can be very weak or absent.
	is a kind of Bp star
helium-strong star	has definition B star in which the helium lines are stronger than in normal stars. One distinguishes usually the extreme helium stars (also called hydrogen-deficient stars), in which no trace of hydrogen is seen, and the intermediate helium-rich stars, in which the hydrogen lines are still visible, but weaker than in normal stars. Related to these objects are the hydrogen deficient C stars.
	is a kind of B star
helium-weak star	has definition B-type star in which the helium lines are weaker than in normal stars.
	is a kind of Bp star
Helix Nebula	has definition A planetary nebula with the largest known angular diameter.
	has distance 140 pc
Helix nebula	has distance 450 light years
	has image
	has synonym NGC 7293
Helix Nebula	has synonym NGC 7293
	is a part of Aquarius
	is an instance of planetary nebula
Helix nebula	is an instance of planetary nebula
	is part of Aquarius
henry	has base unit m2·kg·s-2·A-2
	has symbol H
	has unit Wb·A-1
	is an instance of inductance unit
	is an instance of named derived SI unit
Henry Draper catalog	has number of objects 225300
	has object properties position, spectral type and magnitude
	has publication date 1924
	is a kind of star catalog
Hera	has definition Unofficial name for Jupiter VII.
	has discoverer Perrine
	has discovery date 1905
	has eccentricity e = 0.21
	has inclination i = 28°
	has orbital period P = 259.65 days
	has synonym Jupiter VII
	is a part of Jupiter
	is an instance of natural satellite
Hercules	has acronym Her
	has boundary
	has genitive Herculis
	has historical origin Hercules defeated the Nemean Lion (Leo), the many-headed beast (Hydra) and the little crab (Cancer)
	is a part of celestial sphere
	is an instance of constellation
Hercules cluster	has definition An unsymmetrical cluster. Half of the galaxies are spiral or irregular and about half elliptical or S0. It contains a rather large number of disturbed and peculiar galaxies. The "missing mass", if present, must constitute more than 95% of the total.
	has number of galaxies 75
	has redshift z = 0.036
	has synonym 3U 1551 + 15
	is a part of Hercules
	is a part of Local Supercluster
	is an instance of galaxy cluster
Hercules X-1	has definition An X-ray pulsar, a member of an occulting binary system. The visible component has been identified as the blue variable HZ Herculis, whose spectrum varies from late A or early F to B. Her X- l has a pulsation period of 1.2378 seconds, presumably its rotation period, and exhibits a 35-day quasi-periodicity in the X-ray region (but not in the optical). It is probably a rotating neutron star in a circular orbit with a mass of about 0.7 Msun, which is accreting matter from HZ Her. The orbital period is stable, but the pulsation period is speeding up at a rate of about 1 part in 105 per year. The X-ray eclipse lasts 0.24 days.
	has distance 5 kpc
	has eccentricity e < 0.1
	has eclipse duration 0.24 days (in X-rays)
	has orbital period 1.7 days
	has synonym 3U 1653+35
	is a part of Hercules
	is an instance of eclipsing binary
	is an instance of X-ray pulsar
hertz	has base unit s-1
	has definition A unit of frequency equal to one cycle (or wave) per second.
	has symbol Hz
	is a kind of frequency unit
	is an instance of named derived SI unit
Hertzsprung	is an instance of 19th century scientist
	is an instance of astronomer
Hestia	has definition Unofficial name for Jupiter VI.
	has discoverer Perrine
	has discovery date 1904
	has eccentricity e = 0.16
	has inclination i = 29°
	has orbital period P = 250 days
	has synonym Jupiter VI
	is a part of Jupiter
	is an instance of natural satellite
heterotic e-string theory	has definition One of the five superstring theories; involves closed strings whose right-moving vibrations resemble those of the Type II string and whose left-moving vibrations involve those of the bosonic string. Differs in important but subtle ways from the Heterotic-O string theory.
	has synonym E8 × E8
	is a kind of heterotic string theory
heterotic o-string theory	has definition One of the five superstring theories; involves closed strings whose right-moving vibrations resemble those of the Type II string and whose left-moving vibrations involve those of the bosonic string. Differs in important but subtle ways from the Heterotic-E string theory.
	has synonym O(32)
	is a kind of heterotic string theory
heterotic string theory	has definition Gross's version of string theory in which space-times of different dimensions are associated with the same closed loop.
	is a kind of superstring theory
HF band	has frequency 3 to 30 MHz
	has wavelength 10 to 100 m
	is a kind of radio
Hidalgo	has asteroid number 944
	has definition Asteroid with the largest known orbit with the second highest inclination to the ecliptic and second highest eccentricity of any asteroid.
	has diameter 20 km
	has discoverer Baade
	has discovery date 1920
	has eccentricity e = 0.66
	has inclination 42°.5
	has orbirtal period 13.7 years
	has semi-major axis a = 5.8 AU
	is a part of asteroid belt
	is an instance of asteroid
hierarchy problem	has definition In the context of grand unified theories, the hierarchy problem is our inability to understand theoretically why the energy scale at which the unification becomes apparent, about 1016 GeV (billion electron volts), is so much higher than other energy scales of relevance to particle physics, such as the mass/energy of a proton, which is only 1 GeV.
	is an instance of problem
Higgs boson	has definition A hypothetical, spinless particle that plays an important role in the Glashow-Weinberg-Salam electroweak theory (and in other theories involving spontaneous symmetry breaking, e.g. GUTs).
	has definition The particle or particles associated with the bundles of energy in the Higgs field. Such particles are analogous to the photons that are associated with the electromagnetic field. The standard model of particle physics predicts one electrically neutral Higgs particle which has not yet been found, but which will be sought in upcoming particle accelerator experiments. The grand unified theories predict many Higgs particles, but they are too massive to be accessible at existing or foreseeable accelerators.
	is a kind of boson
	is a kind of hypothetical particle
High Energy Astrophysics Science Archive Research Center	HEASARC -has URL: http://heasarc.gsfc.nasa.gov
	is an instance of astronomical institution
high energy detector	has definition Device for recording the presence of subatomic particles. A typical modem detector consists of an array of electronic sensors connected to a computer, capable of recording the paths of the particles as they fly out from the collision site in a particle accelerator.
	is a kind of instrument
High energy peaked BL Lac object	has acronym HBL
	is a kind of BL Lacertae
high energy physics	is a kind of physics
high energy physics institution	is a kind of institution
high proper motion star	has proper motion high
	is a kind of high-velocity star
high-velocity star	has definition A star whose U and/or V and/or W velocities are much greater or much less than zero. Such stars usually have eccentric orbits around the Galaxy.
	has definition Late type stars whose spatial velocities are greater than 100 km s-1. Other authors prefer the definition, with radial velocities greater than 60 km s-1.
	has spatial velocity > 100 km s-1
	is a kind of star
higher-dimensional supergravity	has definition Class of supergravity theories in more than four spacetime dimensions.
	is a kind of supergravity
highly polarized quasar	has acronym HPQ
	is a kind of quasar
Hiltner Telescope	has altitude 1938 m
	has aperture 2.34 m
	has comment Mirrors repolished 1991
	has creation date 1986
	has focal ratio f/2.07, 13.5
	has latitude 31° 57' N
	has location Kitt Peak, Arizona, US
	has longitude 111° 37' W
	has mirror maker Contraves (USA)
	has mirror type Cer-Vit
	has mounting Equatorial fork, friction-disk drives
	has mounting manufacturer DFM Engineering, L & F Industries
	has owner Michigan-Dartmouth-MIT Obs.
	has synonym Hiltner 2.3 m
	is an instance of Fork equatorial telescope
	is an instance of optical telescope
	is an instance of Ritchey-Chrétien
Hind's nebula	has definition A reflection nebula illuminated by the star T Tauri. It is remarkable for its changes in brightness.
	has discoverer Hind
	has discovery date 1852
	has synonym NGC 1554, NGC 1555
	is a part of dust
	is a part of Taurus
	is an instance of reflection nebula
Hiparcos catalog	is a kind of star catalog
Hipparcos	is an instance of ESA satellite
Hirayama family	has definition A group of asteroids with similar orbital elements. The members of a given family are widely believed to have resulted from collisions between larger parent bodies.
	is a kind of asteroid
	is a part of asteroid belt
HK line	is a kind of interstellar line
HK lines	has definition Two spectral lines of singly ionized calcium. The second strongest interstellar line.
	has species Ca II
	is a kind of Fraunhofer line
Hobby-Eberly Telescope	has altitude 2002 m
	has aperture 9.2 m equivalent
	has comment A project of five universities in US and Germany; 91 spherical mirrors with combined focus for spectroscopy
	has creation date 1997
	has focal ratio (f/1.4) f/4.7
	has latitude 30° 41' N
	has location Mount Fowlkes, Texas, US
	has longitude 104° 01' W
	has mirror maker Univ. of Texas, Penn. State
	has mounting altazimuth fixed in altitude but rotates in azimuth
	has optical design Spherical figure
	has owner University of Texas
	has purpose spectroscopic survey telescope
	is an instance of altazimuth telescope
	is an instance of optical telescope
	is an instance of reflector
hold-time	has definition The time taken to use up all the liquid cryogens, like LN2, in a cooled CCD cryostat.
	is an instance of time
Holmberg radius	has definition The radius of an external galaxy at which the surface brightness is 26.6 mag arcsec-2. This criterion was developed by Holmberg in 1958 to estimate the actual dimensions of the major and minor axes of a galaxy without regard to its orientation in space.
	is an instance of radius
holmium	has image
	has ocean oxidation state III
	is a kind of rare Earth
	is a kind of recycled oceanic element
hologram	has definition An interferometric method of recording information about the three-dimensional nature of an object which relies on preserving both the amplitudes and phases of the wavefronts which reach the detector, instead of merely the amplitudes. Hologram means "whole record". The basic principle was outlined by D. Gabor in 1948.
	is a kind of integrating detector
honeycomb mirror	has definition A construction method for a large mirror in which the back is hollowed-out to leave a ribbed structure that resembles a honeycomb.
	is a kind of mirror
Hooker Telescope	has altitude 1742 m
	has aperture 2.5 m
	has comment telescope out of service 1985-92
	has creation date 1917
	has focal ratio f/5, 16, 30
	has latitude 34° 13' N
	has location Mount Wilson, Calif., US
	has longitude 118° 03' W
	has mirror maker G.W. Ritchey from Saint-Gobain (Paris)
	has mirror type plate-glass
	has mounting manufacturer FG. Pease and Fore River Shipyards
	has owner Mount Wilson Observatory
	has synonym 100 inch
	is an instance of Cassegrain
	is an instance of English equatorial telescope
	is an instance of optical telescope
horizon	has definition A plane perpendicular to the line from an observer to the zenith. The great circle formed by the intersection of the celestial sphere with a plane perpendicular to the line from an observer to the zenith is called the astronomical horizon.
	has definition The maximum distance that an observer can see. In cosmology, our horizon is the distance from us that light has traveled since the beginning of the universe. Objects more distant than our horizon are invisible to us because there hasn't been enough time for light to have traveled from there to here.
	is a kind of plane
horizon problem	has definition A problem of the traditional big bang theory (without inflation) related to the large scale uniformity of the observed universe. The problem is seen most clearly in the cosmic background radiation, which is believed to have been released at about 300000 years after the big bang, and has been observed to have the same temperature in all directions to an accuracy of one part in 100,000. Calculations in the traditional big bang theory show that the sources of the background radiation arriving today from two opposite directions in the sky were separated from each other, at 300000 years after the big bang, by about 100 horizon distances. Since no energy or information can be transported further than one horizon distance, the observed uniformity can be reconciled only by postulating that the universe began in a state of near-perfect uniformity. See also flatness problem.
	has definition A quandary in standard big bang theory, which indicates that few of the particles of the early universe would have had time to be in causal contact with one another at the outset of cosmic expansion. It appears to have been resolved in the inflationary universe theory.
	has definition Cosmological puzzle associated with the fact that regions of the universe that are separated by vast distances nevertheless have nearly identical properties such as temperature. Inflationary cosmology offers a solution.
	has definition The puzzle that widely separated regions of the universe are observed to share the same physical properties, such as temperature, even though these regions were too far apart when they emitted their radiation to have exchanged heat and homogenized during the time since the beginning of the universe. In particular, we detect the same intensity of cosmic radio waves (cosmic background radiation) from all directions of space, suggesting that the regions that emitted that radiation had the same temperature at the time of emission. However, at the time of emission, when the universe was about 1 million years old, those regions were separated by roughly 100 million light years, much exceeding the distance light or heat could have traveled since the big bang. The horizon problem is also called the causality puzzle. (See horizon.)
	has synonym homogeneity problem
	is a kind of problem
horizontal branch star	has color blue to yellow
	has definition A metal-poor star after it has undergone the helium flash and begins to quietly burn helium into carbon and oxygen in its core and hydrogen in a surrounding envelope.
	has location on H-R diagram extends shortward from the asymptotic branch at an approximately constant absolute bolometric magnitude of about 0.3
	is a kind of metal-poor star
horizontal parallax	has definition The difference between the topocentric and geocentric positions of an object, when the object is on the astronomical horizon.
	is a kind of parallax
Horologium	has acronym Hor
	has genitive Horologii
	has historical image
	has historical origin the clock in honor of Christian Huygens, the inventor of the pendulum clock in 1656-57
	has synonym Clock
	has synonym Horologium Oscillitorium
	is a part of celestial sphere
	is an instance of constellation named by de Lacaille
Horsehead Nebula	has definition An absorption nebula in the middle of Orion.
	has synonym NGC 2024
	is a part of dust
	is an instance of dark nebula
Horseshoe equatorial telescope	has mounting Horseshoe equatorial
	is a kind of equatorial telescope
hot dark matter	has definition Any form of dark matter which was relativistic at its point of decoupling.
	is a kind of dark matter
hour	has symbol h
	has value in SI unit 60 min = 3600 s
	is an instance of non SI unit
hour circle	has definition A great circle passing through the celestial poles - i.e., perpendicular to the celestial equator.
	is a kind of great circle
Hourglass Nebula	has definition A compact H II region in the center of Lagoon Nebula.
	has distance 8000 light-years away
	has image
	has synonym MyCn18
	is a part of Lagoon Nebula
	is an instance of compact H II region
	is an instance of planetary nebula
Hoyle-Narlikar theory	has definition A reformulation of the general theory of relativity that incorporates and extends Mach's principle (q.v.). In this theory, the inertial mass of a particle is a function of the masses of all other particles, multiplied by a coupling constant which is a function of cosmic epoch. In cosmologies based on this theory, the gravitational constant G decreases strongly with time.
	is a kind of cosmology theory
HR 4247	has B-V magnitude 1.04
	has declination +34 12 53
	has right ascension 10 53 18.6
	has spectral type K0III-IV
	has V magnitude 3.83
	is a part of Leo Minor
	is an instance of giant
	is an instance of K star
	is an instance of naked eye star
HR 4796A	has image
	is an instance of star
HRS	has definition High-Resolution Spectrograph (Hubble).
	is a kind of diffraction grating spectrograph
Hubble	has birth date November 20, 1889
	has career 1914-1917 : Assistant, Yerkes Observatory 1919-1953 : Mt. Wilson
	has death date September 28, 1953
	has degree 1910 : BSc. U. Chicago 1913 : law, Oxford 1917 : PhD. Yerkes, ("Photographic Investigations of Faint Nebulae", Frost as supervisor)
	has image
	has name Edwin Powell Hubble
	has orbituary Adams, W.S. : 1954, Observatory 74, 32. Humason, M.L. : 1954, MNRAS 114, 291. Robertson, H.P. : 1954, PASP 66, 120. Sandage, A. : 1989, JRASC 83, 352.
	is an instance of 19th century scientist
	is an instance of astronomer
Hubble 5	has distance 2200 light years
	has image
	is an instance of planetary nebula
	is part of Sagittarius
Hubble constant	has definition According to Hubble's law, discovered by Edwin Hubble in 1929, distant galaxies are receding from us, on average, with a speed equal to the product of the Hubble constant and the distance to the galaxy. Hubble's "constant" is independent of distance, but actually decreases slowly in time as the expansion is slowed by the gravitational pull of each galaxy on all the others. The present value is somewhere between 15 and 30 kilometers per second per million light-years.
	has definition Hubble's constant in units of 100 km s-1 Mpc-1.
	has definition The constant of proportionality in the Hubble law. Its value must vary with time, so it is often referred to as the Hubble parameter. The Hubble constant is generally used to mean the value of the Hubble parameter at the current epoch, and is somewhere between 50 and 100 km/s/Mpc with possibly a value close to 75 km/s/Mpc.
	has definition The present expansion rate of the universe, in units of kilometers per second per megaparsec. The larger the Hubble constant, the younger the universe.
	has definition The rate at which the universe expands, equal to approximately fifty kilometers of velocity per megaparsec of distance.
	has definition The rate of expansion of the universe. The Hubble constant is equal to the recessional speed of a distant galaxy, divided by its distance from us. Assuming a homogeneous and isotropic universe, the recessional speed of a distant galaxy is proportional to its distance; thus the Hubble constant as determined by any receding galaxy should be the same, yielding a universal rate of expansion of the universe. According to estimates, the current value of the Hubble constant is approximately 100 km/s/Mpc, meaning that the distance between any two distant galaxies will double in about 10 billion years at the current rate of expansion.
	has rate of change non-zero because gravity is slowing down the rate of expansion of the universe
	has symbol H0
	has unit km/s/Mpc
	has value 75 km/s/Mpc
	is an instance of astronomical constant
Hubble flow	has definition The movement of the galaxies away from us caused by the expansion of the Universe.
	is a kind of galaxy motion
Hubble law	has definition A relation which states that recessional speed is proportional to distance for a homogeneous and isotropic universe. Galaxies moving away from us with a speed precisely following this relation are said to follow the Hubble flow. Because the actual universe is not precisely homogeneous, with lumpiness arising from clustering of galaxies and voids of empty space, the motions of actual galaxies deviate somewhat from the Hubble flow.
	is a kind of cosmology theory
Hubble nebula	has definition A cometary nebula whose apex star is R Mon.
	has synonym NGC 2261
	is a part of dust
	is an instance of cometary nebula
Hubble radius	has definition The radius of the observable universe ().
	has symbol c/H
	has value > 1027 cm
	is an instance of astronomical constant