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variable
subject			fact

variable	has name designated with R, S, T, U, V, W, X, Y, or Z and the genitive of the latin constellation name RR, RS, RT, RU, RV, RW, RX, RY, or RZ and the genitive of the latin constellation name when the single letter designations are exhausted AA...AZ, BB...BZ, etc. (omitting J), which ends with QQ...QZ and the genitive of the latin constellation namewhen the RR...RZ designations are exhausted V 335, V 336, etc., when the double letter designations are exhausted
	has observational problem some difficulty in distinguishing between various kinds
	has observable variation time scale within a period of decades
	has light curve
	has optical brightness variation 0.2 magnitudes or greater
	has amplitude
	has definition 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).
	has definition 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.
	has definition 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.
	has definition 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)
	is a kind of star
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
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 variable :

• Be star (1 kind, 9 facts) - Irregular variables of spectral type B (or occasionally O or A) with hydrogen emission lines in their spectra. The Be phenomenon involves rapid stellar rotation, circumstellar shells, and mass loss., Non-supergiant B-type stars, which have shown emission in at least one of the Balmer lines at some time.
• bright blue variable (1 kind, 3 facts) - Early-type high-luminosity star with peculiar spectra and large-amplitude light variations over a long time scale.
• irregular variable (39 kinds, 187 facts)
• luminous blue variable (5 facts) (S Dor variable, Hubble-Sandage variable) - A variable-star designation for the high-luminosity early type objects.
• periodic variable (36 kinds, 212 facts)
• semiregular variable (2 kinds, 15 facts) - A class of giant and supergiant pulsating stars of spectral class M, K, N, R, or S with a periodic (or semiperiodic) light curve of varying amplitude.
• symbiotic star (1 kind, 7 facts) (combination variable) - Object exhibiting a spectrum corresponding to a low-temperature star (generally a giant) plus emission lines corresponding to a hot plasma., A term originally used by P. Merrill to describe stars of two essentially dissimilar kinds which seem to occur together and which seem to "need" each other. In practice, it has come to signify a peculiar group of objects (usually spectral type Me) that display a combination of low-temperature absorption spectra and high-temperature emission lines. These objects undergo semiperiodic nova-like outbursts and display the spectral changes of a slow nova superposed on the features of a late-type star. Their spectra are midway between those of planetary nebulae and true stellar objects. A symbiotic star is now usually taken to be a small, hot, blue star surrounded by an extensive variable envelope. As of 1973 about 30 were known.

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