Glossary term: Cepheid Variable

Description: Cepheids are pulsating variable stars whose variability is caused by periodic oscillation of the outer layers of the star. They are named after the prototype star, Delta Cephei. An important feature of Cepheids is that their period is closely related to their luminosity. This is the famous period–luminosity relationship revealed by Henrietta Leavitt in 1908. Using this relationship, the absolute brightness of a Cepheid can be calculated from the pulsation period. The difference between the easily observable apparent brightness and absolute brightness derived from the relationship is indicative of the distance of both the given Cepheid and the external galaxy hosting this variable star. Thus Cepheids are primary distance indicators in establishing the cosmic distance scale.

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