- Stars with a fluctuating output of light (or other electromagnetic radiation). Many types of variable stars are known. The most spectacular kind of variation is that of novae and supernovae, which are not counted as mainstream variables. Apart from these, the principal kinds include eclipsing binaries such as the prominent variable Algol in Perseus, which vary because they consist of two stars which periodically cut off each other’s light from observers on the Earth, and Cepheids, RR Lyrae stars, and R Coronae Borealis stars. Variability is often associated with interactions between members of double star pairs, and includes high-energy variability seen in X-rays rather than visible light Main-sequence stars like the Sun are rarely variable: stars off the main sequence, especially those near the beginning and end of their lives, are the usual candidates for variability. Despite our sophisticated understanding of the nature of variable star types, their light curves are still one of the major observational targets open to amateur astronomers with modest telescopes. See Star classification for the unique method used to name variables.
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