CASTOR - is the second brightest star in the constellation Gemini and one of the brightest stars in the nighttime sky. Although it has the Bayer designation "alpha", it is actually fainter than (Pollux).Castor and Pollux are the two "heavenly twin" stars that give the constellation Gemini (meaning "twins" in Latin) its name. The name Castor is traditionally thought by some people to carry the meaning "Beaver", after the generic name of the beaver. Actually the name Castor refers specifically to Castor, one of the twin sons of Zeus and Leda. The the period of revolution is around 350 years. Each of the components of Castor is itself a spectroscopic binary, making Castor a quadruple star system. Castor has a faint companion separated from it by about 72" but having the same parallax and proper motion, this companion is also a spectroscopic binary with a period slightly less than 1 day. Castor can be considered to be a sextuple star system, with six individual stars gravitationally bound together.
