A type of variable star that varies regularly in proportion to its luminosity. They are important in astronomy and are known as 'standard candles' as their distance from Earth can be easily calculated.
Cepheid variables are divided into two subclasses, classical (type I) Cepheids and type II Cepheids. The two classes differ in mass, age and evolutionary history. The term Cepheid is named after star Delta Cephei (δ Cep) the first of its type to be identified by John Goodricke in 1784. The characteristics of classical Cepheids were discovered by Henrietta Swan Leavitt in 1908.