Cepheids are giant stars that regularly pulsate in size and change in brightness. As the star increases in size, its brightness decreases; then, the reverse occurs.
Cepheid Variables are not be permanently variable; the fluctuations generally pertain to an unstable phase the star is going through. Polaris and Delta Cephei are examples of Cepheids.
Although interesting in their own right, from a stellar modeling perspective, much of the importance of cepheid variables derives from the relation between their period and their absolute brightness. This relationship means that, once calibrated, they can be used as 'standard candles' to find the distances to distant stellar associations, including other galaxies.
see also Classical Cepheids, W-Virginis Stars.
Text by M. Alan Kazlev and Chris Clowes
Initially published on 24 September 2001.