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Cepheid variable One of an important class of variable stars that pulsate in a regular manner, accompanied by changes in luminosity. Cepheids can expand and contract up to 30% in each cycle. The average luminosity is 10,000 times that of the Sun. Cepheids became important in cosmology (1912) when US astronomer Henrietta Leavitt discovered a relationship between the period of light variation and the absolute magnitude of a cepheid. This period-luminosity law enables the distances of stars to be ascertained.
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