A Cepheid variable is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute stellar luminosity.

Because of this correlation (discovered by Henrietta Swan Leavitt in 1912), Cepheid variables can be used as a standard candle to determine the distance to their host globular clusters or galaxies. Since the period-luminosity relation can be calibrated with great precision using the nearest Cepheid stars, the distances found with this method are among the most accurate available.

Description

A Cepheid is usually a population I giant yellow star, pulsing regularly by expanding and contracting, resulting in a regular oscillation of its luminosity. The luminosity of cepheid stars range from 10³ to 10⁴ times that of the Sun.

Use as a standard candle

Notes

• Some Cepheid stars (for example Polaris), have shown a decrease in their oscillation over a period of few tens of years, and now are virtually constant.

• Cepheid stars are sometimes divided into two types, type I Cepheid and type II Cepheid. The latter type, composed of Population II stars, are now usually called W Virginis variables, and show a similar behaviour.

See also: RR Lyrae variable, Hubble Constant