Cepheids
Cepheids are a type of variable star that pulsates radially, varying in both temperature and diameter to produce brightness changes with a well-defined stable period and amplitude. They are important distance indicators in astronomy, particularly in the measurement of distances to galaxies and the expansion rate of the universe. Cepheids are used as standard candles to determine the luminosity of a star, which can then be used to calculate its distance from Earth. The period-luminosity relationship for Cepheids was discovered by Henrietta Swan Leavitt in 1912, and this relationship is still used today to measure distances to galaxies within the Local Group and beyond.
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