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[[Image:Gemini constellation map.png|thumb|right|338px|Location of Castor in the constellation of Gemini]]

[[Image:Gemini constellation map.png|thumb|right|338px|Location of Castor in the constellation of Gemini]]

'''Castor''', also known as '''Alpha Geminorum''', is a star system in the constellation [[Gemini]].  Despite the star's alpha [[Bayer designation]], it is the second brightest star of the Gemini constellation, with a total apparent magnitude of 1.58.<ref name="illinois">http://stars.astro.illinois.edu/sow/castor.html</ref>  Originally thought as a single binary star system, the Castor system is actually three sets of tight, spectroscopic binary stars.  Based on measurements from the [[Hipparcos]] mission, it is estimated that the Castor system is 51.6 light years away.<ref name="illinois">http://stars.astro.illinois.edu/sow/castor.html</ref>

'''Castor''', also known as '''Alpha Geminorum''', is a star system in the constellation [[Gemini]].  Despite the star's alpha [[Bayer designation]], it is the second brightest star of the Gemini constellation, with a total apparent magnitude of 1.58.<ref name="illinois">http://stars.astro.illinois.edu/sow/castor.html</ref>  Originally thought as a single binary star system, the Castor system is actually three sets of tight, [[Binary_stars#Spectroscopic_Binaries|spectroscopic binary stars]].  Based on measurements from the [[Hipparcos]] mission, it is estimated that the Castor system is 51.6 light years away.<ref name="illinois">http://stars.astro.illinois.edu/sow/castor.html</ref>

The modern name for the [[star]], Castor, is named for the character of the same name in [[Greek mythology]], who was one of the twin sons of [[Zeus]] and Leda.  During the era of [[ancient Greece]] though, the star was called Ἀπόλλων, (pronounced apóllɔːn), meaning Apollo. In [[Arabic]], the star was called ''Al Rās al Taum al Muḳaḍḍim'', meaning the Head of the Foremost Twin.<ref>http://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Gemini*.html</ref>

The modern name for the [[star]], Castor, is named for the character of the same name in [[Greek mythology]], who was one of the twin sons of [[Zeus]] and Leda.  During the era of [[ancient Greece]] though, the star was called Ἀπόλλων, (pronounced apóllɔːn), meaning Apollo. In [[Arabic]], the star was called ''Al Rās al Taum al Muḳaḍḍim'', meaning the Head of the Foremost Twin.<ref>http://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Gemini*.html</ref>