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physical object > natural object > celestial body

celestial body
subject			fact

celestial body	has spectra
	has definition natural object visible in the sky
	is a kind of natural object
physical object	has location or center of gravity
	has angular momentum
	has mass
	has velocity
	has momentum
	has temperature
	has volume
	has extent
	has material

Kinds of celestial body :

• asteroid (17 kinds, 174 facts) (minor planet, planetoid) - 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., 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, 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).
• asteroid belt (4 facts) - 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.
• collection of stars (256 kinds, 1350 facts) - Two or more stars forming a gravitationally bound system
• comet (2 kinds, 9 facts) - A diffuse body of gas and solid particles (such as CN, C₂, NH₃, and OH), which orbits the Sun. The orbit is usually highly elliptical or even parabolic (average perihelion distance less than 1 AU; average aphelion distance, roughly 10⁴ AU). Comets are unstable bodies with masses on the order of 10¹⁸ g whose average lifetime is about 100 perihelion passages. Periodic comets comprise only about 4% of all known comets. Comets are obviously related in some manner to meteors, but no meteorites from a comet have ever been recovered. Observations of comets Bennett and Kohoutek have established that a comet is surrounded by a vast hydrogen halo.
• gamma ray source (1 kind, 10 facts)
• Messier object (47 kinds, 489 facts) - an object assigned a number by Charles Messier
• natural satellite (33 kinds, 282 facts) - Body orbiting a planet. Since 1957 the term has also been applied to man-made (artificial) satellites; many astronomers make the distinction by calling natural satellites moons (and the Earth's natural satellite the Moon).
• nebula (64 kinds, 338 facts) - The term "nebula" was previously applied to all kinds of hazy patches in the sky, many of which are now recognized to be clusters or galaxies. (See also diffuse nebula, gaseous nebula, dark nebula.), Indistinct, nonterrestrial objects visible in the night sky. "Bright" nebulae glow with light emitted by the gas of which they are composed ("emission" nebulae) or by reflected starlight ("reflection" nebulae) or both. "Dark" nebulae consist of clouds of gas and dust that are not so illuminated. "Planetary" nebulae are shells of gas ejected by stars. Spiral nebulae are galaxies., An irregularly shaped cloud of interstellar gas or dust whose spectrum may contain emission lines (emission nebula) or absorption lines characteristic of the spectrum of nearby illuminating stars (reflection nebula).
• NGC object (4 facts) - an object assigned a number in the New General Catalog of non-stellar objects
• planet (14 kinds, 251 facts) - An object that formed in the disk surrounding a star. Unlike stars, planets do not produce light of their own but merely reflect that of the star(s) they orbit. Planets can have natural satellites.
• radio source (39 kinds, 174 facts) - A source of extraterrestrial radio radiation. The strongest known is Cassiopeia A, followed by Cyg A and the Crab Nebula (Tau A) (the capital letters following the name of a constellation refer to the radio sources of the constellation, A being the strongest source). Radio sources are divided into two main categories: Class I, those associated with our Galaxy (which is a weak radio source), and Class II, extragalactic sources. Most radio sources are galaxies, supernova remnants, or H II regions.
• ring (6 kinds, 25 facts) - A system of four concentric rings, only about 2-4 km thick. The outermost ring is ring A, then comes Cassini's division, then ring B (also called the bright ring), then Lyot's division, then ring C (the crepe ring), then ring D (discovered in 1969). The rings are a swarm of solid particles, probably jagged rocks about 1 meter to 1 km across (1973), not ice as previously had been assumed, inside the Roche limit. Bobrov (1969) estimates the total mass of the rings to be about 0.01 the lunar mass.
• ring gap (3 kinds, 17 facts) - A gap between the rings of Saturn.
• solar system (1 kind, 5 facts) - A star with planets
• star (353 kinds, 2096 facts) - a spinning ball of hot gases held together by gravity, A celestial object that generates energy by means of nuclear fusion at its core. To do this it must have more than about 0.08 the sun's mass. If, for instance, the planet Jupiter were some fifty to one hundred times more massive than it is, fusion reactions would transpire in its core and it would be a star. See planet.
• Universe (3 facts) - The total celestial cosmos. According to Gott et al. the universe seems to be on a large scale isotropic, homogeneous, matter-dominated, and with negligible pressure. The total proper mass content of about 10²³ M_sun (Sandage derives 10⁵⁶ g from his determination of the deceleration parameter q₀) and radius of about 2 × 10²⁸ cm are the order of magnitude that most cosmologists would accept if the universe is bounded. Total mass contributed by luminous matter, about 3 × 10⁵³ g (see mass discrepancy). Age about 18 × 10⁹ yr for a Hubble constant H₀ = 55 km s^-1 Mpc^-1.
• X-ray source (23 kinds, 150 facts) - A class of celestial objects whose dominant mechanism of energy dissipation is through X-ray emission. Galactic X-ray sources appear optically as starlike objects, peculiar in their ultraviolet intensity, variability (on time scales ranging from milliseconds to weeks), and spectral features. All known compact X-ray sources are members of close binary systems; a current popular model is mass accretion onto a compact object from a massive companion. (Four X-ray sources - all variable - are known to be associated with globular clusters.) The 21 known extended X-ray sources associated with clusters of galaxies seem to be clouds of hot gas trapped in the cluster's gravitational field.