Changes

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]].

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]].

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>

Cepheid stars pulsate in regular intervals typically in the range from 1 to 100 days. The stars themselves are yellowish giants or [[supergiant]]s, 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>

==Discovery and History==

==Discovery and History==

==Types of Cepheids==

==Types of Cepheids==

Cepheid variables fall into one of two categories, Type I, also known as ''classical Cepheids'' or [[Delta Cepheid]] stars, and Type II, also known as [[W Virginis star|W Virginis stars]].  The Type I Cepheids are extreme [[Metallicity|population I stars]] located in the spiral arms of galaxies.  Metal rich and some 4 times as luminous as Type II Cepheids, these stars typically have a variation period lasting 5 to 10 days in lenght. Type II Cepheids on the other hand are [[Metallicity|metal-poor population II stars]].  Their periods of variability typically ranges from 10 to 30 days in length, and are primarily found in [[elliptical galaxy|elliptical galaxies]], [[globular cluster|globular clusters]], and galactic halos.<ref>http://adsabs.harvard.edu/abs/2002PASP..114..689W</ref>

Cepheid variables fall into one of two categories, Type I, also known as ''classical Cepheids'' or [[Delta Cepheid]] stars, and Type II, also known as [[W Virginis star]]s.  The Type I Cepheids are extreme [[Metallicity|population I stars]] located in the spiral arms of galaxies.  Metal rich and some 4 times as luminous as Type II Cepheids, these stars typically have a variation period lasting 5 to 10 days in lenght. Type II Cepheids on the other hand are [[Metallicity|metal-poor population II stars]].  Their periods of variability typically ranges from 10 to 30 days in length, and are primarily found in [[elliptical galaxy|elliptical galaxies]], [[globular cluster]]s, and galactic halos.<ref>http://adsabs.harvard.edu/abs/2002PASP..114..689W</ref>

== Sources ==

== Sources ==