Cepheid variable

Yellow supergiant star that varies regularly in brightness every few days or weeks as a result of pulsations. The time that a Cepheid variable takes to pulsate is directly related to its average brightness; the longer the pulsation period, the brighter the star.

This relationship, the period luminosity law (discovered by US astronomer Henrietta Leavitt), allows astronomers to use Cepheid variables as ‘standard candles’ to measure distances within our Galaxy and to nearby galaxies. They are named after their prototype, Delta Cephei, whose light variations were observed in 1784 by English astronomer John Goodricke.