A type of pulsating variable star with a precise period-luminosity relationship, where brighter stars have longer pulsation periods. These stars serve as 'standard candles' for measuring cosmic distances because their true brightness can be determined from their pulsation period.
Named after Delta Cephei, the prototype star in the constellation Cepheus, discovered by John Goodricke in 1784. The crucial period-luminosity relationship was discovered by Henrietta Swan Leavitt in 1912, transforming these stars into the primary tool for measuring galactic distances.
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