Variable Star

Star whose luminosity varies over time. Broadly speaking, variable stars are of two types: (1) stars that are intrinsically variable, that is, their luminosity actually changes, for example because the star periodically swells and shrinks; (2) eclipsing and rotating variables, where the apparent changes in brightness are a perspective effect. The first 334 variable stars discovered in a constellation are given a one or two letter code such as R Scuti or UV Ceti. Other variable stars are designated V335, V336, etc. For example, Proxima Centauri is known to variable star astronomers as V645 Centauri.


Image source: http://en.wikipedia.org/wiki/File:HR-vartype.svg.