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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