Cepheid variables

Cepheid variables are stars with distinct brightness patterns, named after the first such star discovered in the constellation Cepheus. Leavitt worked out a method for determining the luminosity of a Cepheid variable from its period. Once its luminosity was known, its distance could be calculated from its apparent brightness.
 Henrietta Swan Leavitt England 1912 Cepheid variables

Cepheid variables are stars with distinct brightness patterns, named after the first such star discovered in the constellation Cepheus. Leavitt worked out a method for determining the luminosity of a Cepheid variable from its period. Once its luminosity was known, its distance could be calculated from its apparent brightness.