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star
subject			fact

star	has star surface temperature
	has spectral type
	has V magnitude
	has B magnitude
	has U magnitude
	has position on celestial sphere from the point of view of Earth
	has parallax from the point of view of Earth's orbit
	has proper motion
	has radiation at surface which is diffused out from the hotter core
	has energy source gravitational contraction and or fusion
	has energy production which takes place primarily within the core
	has surface density which depends on luminosity class
	has surface temperature greater than 1000 Kelvin
	has apparent magnitude
	has absolute magnitude
	has age
	has catalog star catalog
	has material hydrogen, helium
	has velocity determined from proper motion and radial velocity
	has mass greater than 0.08 the sun's mass
	has definition a spinning ball of hot gases held together by gravity
	has definition 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.
	is a kind of celestial body
celestial body	has spectra
physical object	has location or center of gravity
	has angular momentum
	has momentum
	has temperature
	has volume
	has extent

Kinds of star :

• asymptotic branch star (2 facts) - 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.
• Beta Pictoris (4 facts)
• binary star (57 kinds, 339 facts) - A system of two stars orbiting around a common center of gravity. Visual binaries are those whose components can be resolved telescopically (i.e., angular separation > 0'.5) and which have detectable orbital motion. Astrometric binaries are those whose dual nature can be deduced from their variable proper motion; spectroscopic binaries, those whose dual nature can be deduced from their variable radial velocity. At least half of the stars in the solar neighborhood are members of binary (or multiple) systems. (See photometric binaries; optical pairs.)
• bright giant (9 kinds, 94 facts)
• circumpolar star (2 facts) - Star which never sets, from the viewpoint of an observer on Earth.
• composite spectrum star (4 kinds, 14 facts) - Object with a spectrum due to superposition of the spectra of two different stars.
• Delta Del star (4 kinds, 17 facts) - A type of late A-type and early F-type star with very weak Ca II HK lines.
• double star (2 facts) - A "system" of two stars that appear - because of coincidental alignment when viewed from Earth - to be close together; it is, however, an optical effect only, and therefore not the same as a binary star system (although until the twentieth century there were few means of distinguishing double and binary stars).
• dwarf (37 kinds, 340 facts) (d, main sequence star) - Star, like the Sun, that fuses hydrogen into helium at its core. Ninety percent of all stars are main-sequence stars; examples are Sirius, Vega, Altair, and Alpha Centauri A, B, and C., Star that is on the main sequence - that is, a star fusing hydrogen into helium at its core., Star with mass equal to or less than that of the sun. More generally, any star on or below the main sequence in the Hertzprung-Russell diagram.
• early star (111 kinds, 784 facts) - Hot star of spectral types O, B, A, and early F.
• emission line star (58 kinds, 259 facts)
• field star (3 facts) - A star that is not part of any star cluster. Most stars, including the Sun, are field stars., Star distributed at random in space and not belonging to any particular star cluster.
• fundamental star (2 facts) - Star for which coordinates have been determined to a very high degree of accuracy.
• giant (54 kinds, 474 facts) - 1. A star that has evolved off the main sequence and is roughly a hundred times as luminous as the Sun. Giants can be of any color, but yellow, orange, and red giants are the most common. 2. A planet much more massive than Earth. The solar system has four giant planets, all far from the Sun: Jupiter, Saturn, Uranus, and Neptune., High-luminosity star that lies above the main sequence on the Hertzsprung-Russell diagram.
• HD 141569 (4 facts)
• high-velocity star (3 kinds, 14 facts) - A star whose U and/or V and/or W velocities are much greater or much less than zero. Such stars usually have eccentric orbits around the Galaxy., Late type stars whose spatial velocities are greater than 100 km s^-1. Other authors prefer the definition, with radial velocities greater than 60 km s^-1.
• HR 4796A (2 facts)
• hydrogen-deficient star (4 kinds, 26 facts)
• late star (85 kinds, 674 facts) - Star with spectral type later than the sun (G2).
• low-velocity star (2 facts) - A star whose U, V, and W velocities are all near zero. Such stars have nearly circular orbits around the Galaxy.
• manganese star (2 facts) - Star with an anomalously high Mn-Fe ratio, which show deviations from the odd-even effect for phosphorus, gallium, and yttrium.
• metal-poor star (6 kinds, 24 facts)
• metal-rich star (1 kind, 8 facts) (metal-strong star, CN-strong star) - A small subgroup of A-type stars in which the lines of Mg II are very strong., Star having metal-to-hydrogen ratios greater than those of the Hyades.
• naked eye star (88 kinds, 964 facts) - A star visible without visual aids
• neutron star (10 kinds, 60 facts) - A dead, collapsed star that consists mostly of neutrons and is only about 20 kilometers across. Neutron stars are much denser than white dwarfs., A star whose core is composed primarily of neutrons, as is expected to occur when the mean density is in the range 10¹³-10¹⁵ g cm^-3. Under current theories pulsars are assumed to be rotating magnetic neutron stars. A neutron star would probably be only 10-15 km in diameter with a magnetic field of about 10¹² gauss, a density of 10¹³-10¹⁵ g cm^-3 (compared with a white dwarf's maximum density of about 10⁸ g cm^-3) and a central temperature of about 10⁹ K and thus would be both bluer and dimmer than a white dwarf., Remnant of a star after it has exploded as a supernova. Usually optically dim, a neutron star sends out regular or irregular radio emissions and is therefore also called a pulsar. The density of such a star may be unimaginably great although the diameter is generally around only 10 km; the gravitational and magnetic forces are correspondingly vast. It is called a neutron star because in such density, protons fuse with electrons to form neutrons, of which the star is almost entirely composed.
• old star (2 facts) - Star that, according to contemporary stellar evolution theory, have an age comparable to that of the galaxy to which they belong. This is not an observational definition.
• Population I star (5 kinds, 80 facts) (arm population, disk star) - Younger stars, generally formed towards the edge of a galaxy, of the dusty material in the spiral arms, including the heavy elements. The brightest of this Population are hot, white stars., Young star with relatively high abundances of metals, and are usually found in the disk of a galaxy, especially the spiral arms, in dense regions of interstellar gas., Young star typical of those found in galaxy spiral arms., Youngest observed stars, like our sun, formed from hydrogen, helium, and a large range of heavier elements (like carbon and oxygen) believed to have been created in the interiors of earlier Population II stars and Population III stars and then blown out into space.
• Population II star (4 kinds, 25 facts) (halo star) - Older star with relatively low abundances of metals, usually found in the nucleus of a galaxy or in globular clusters. The Sun is a rather old Population I star., Star that has high spatial velocity and low metallicity. This is not an observational definition., Older observed stars formed mostly from hydrogen and helium., Old stars typical of those found in the halo of the Galaxy., Older stars, generally formed towards the centre of a galaxy, containing few heavier elements. The brightest of this Population are red giants.
• Population III star (3 facts) - Star older than Population II stars.
• program star (2 facts) - The star being observed or measured, as contrasted with the comparison stars.
• radio star (13 kinds, 85 facts) - Star with detectable emission at radio wavelengths. They include pulsars, flare stars, some infrared stars, and some X-ray stars.
• spectrum variable (1 kind, 6 facts) - Main-sequence Am or Ap stars whose spectra show anomalously strong lines of metals and rare earths which vary in intensity by about 0.1 mag over periods of about 1-25 days. They are characterized by large magnetic fields (10³-10⁴ gauss) at the surface, small variations in light and color, and small projected rotational velocities. These peculiarities are sometimes interpreted in terms of an oblique rotator.
• subdwarf (3 kinds, 22 facts) (sd) - A metal-poor main-sequence star. On the H-R diagram, subdwarfs lie slightly below the metal-rich Main Sequence, because they are fainter than metal-rich main-sequence stars of the same color., Star whose luminosity is 1.5 to 2 magnitudes lower than that of main-sequence stars of the same spectral type. Subdwarfs are primarily Population II and lie just below the Main Sequence on the H-R diagram., Late-type object whose observed color and absolute magnitude place it below the Main Sequence.
• subgiant (11 kinds, 122 facts) - A star whose position on the H-R diagram is intermediate between that of main-sequence stars and normal giants of the same spectral type.
• supergiant (18 kinds, 167 facts) - An extremely luminous star of large diameter and low density. No supergiants are near enough to establish a trigonometric parallax.
• triple star (2 kinds, 22 facts) - A star system having three stars that revolve around one another.
• variable (86 kinds, 441 facts) - Star whose luminosity changes over periods of time; there are many reasons and many types. Periods vary widely in length and even regularity. Novae and supernovae are classed as variables. The present brightest variable star is Betelgeuse (Alpha Orionis)., A star whose light varies. Some variables vary simply because they consist of two stars, one of which eclipses the other; Algol is the most famous example. Other variables, however, vary because the stars themselves actually change in brightness; the most famous are the Cepheids, RR Lyraes, and Miras, all of which pulsate., A star that varies in luminosity. The first variable discovered in a given constellation has the letter R preceding the name of the constellation. Then S, . . . , Z. Then RR, RS, . . . , Rz, SS, . . . , Sz, . . . , ZZ. Then AA, . . . , AZ (the letter J is never used), BB, . . . , BZ, . . . , QQ, . . . QZ. The next variable (the 335th) is given the designation V335., a star whose apparent magnitude varies by at least 0.1 magnitudes in the visible spectrum (a star whose optical brightness variations can be detected by the human eye)

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