variable star

variable star
a star that varies markedly in brightness from time to time. Also called variable.

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Star whose observed brightness varies noticeably in intensity.

Pulsating variables expand and contract in cycles, pulsating rhythmically in brightness and size. Explosive variables include novas and supernovas, which brighten rapidly due to sudden outbursts of radiant energy; the increased brightness lasts a short time, followed by relatively slow dimming. Eclipsing variable stars are variable only because light from one star is blocked by another in Earth's direction. Hundreds of thousands of variable stars are known. See also binary star; Cepheid variable; flare star; pulsar; T Tauri star.

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 any star whose observed light varies notably in intensity. The changes in brightness may be periodic, semiregular, or completely irregular.

      A brief treatment of variable stars follows. For full treatment, see star: Variable stars (star).

      Variable stars may be classified into three broad types according to the origin and nature of their variability: (1) eclipsing, (2) pulsating, and (3) explosive.

      In an eclipsing variable (eclipsing variable star), one member of a double, or binary (binary star), star system partially blocks the light of its companion as it passes in front of the latter, as observed from Earth. Each time this happens, the brightness of the entire system fluctuates. Such an eclipsing variable is perhaps best exemplified by the binary star Algol, whose name means “blinking demon.”

 Unlike eclipsing binaries, the other two types of variable stars are intrinsically variable—that is to say, their own output of radiant energy fluctuates with time. The pulsating variables expand and contract cyclically, causing them to pulsate rhythmically in brightness and size. The Cepheids (Cepheid variable) and RR Lyrae stars (RR Lyrae star) are typical examples of such variables. The explosive (or eruptive) variables include novas (nova), supernovas (supernova), and similar stars that undergo sudden outbursts of radiant energy, which results in rapid brightening. This increase in brightness lasts only for a short period of time, followed by relatively slow dimming.

      Besides these three major classes, there are also several miscellaneous variables: R Coronae Borealis stars, T Tauri stars, flare stars, pulsars (neutron stars), spectrum and magnetic variables, X-ray variable stars, and radio variable stars. Tens of thousands of variable stars are known.

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Universalium. 2010.

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Look at other dictionaries:

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