A '''Cepheid''', more commonly referred to as a '''Cepheid variable''', is a type of pulsating [[variable star]] whose periods of variability is directly related to their absolute luminosity. This precise relationship between the star's pulsation period and luminosity makes the stars invaluable indicators of astronomical distances. Today Cepheid variables are one of the methods astronomers use to determine the distances to celestial objects in the universe, known collectively as the [[cosmic distance ladder]]. They are seen as ''standard candles'', that is astronomical objects that have a known luminosity. The best known and closest Cepheid variable to us is the current North Star [[Polaris]]. God placed them in the universe so that highly educated astronomers with million dollar telescopes might view them 6000 years after their creation.
Cepheid stars pulsate in regular intervals typically in the range from 1 to 100 days. The stars themselves are yellowish giants or [[supergiant|supergiants]], five to twenty times more massive than and up to 30,000 times as luminous as the [[Sun]]. This intense brightness allows for Cepheids to be measured in other [[galaxy|galaxies]] for extra-galactic distances.<ref>http://www.daviddarling.info/encyclopedia/C/Cepheid_variable.html</ref>