Castor (star)

Castor (star), a star, Alpha Geminorum, of magnitude 1.6, the fainter star of the zodiacal constellation Gemini, or the Twins (see Zodiac). In 1719 it was discovered to be a visual binary star, with components of magnitudes 2.8 and 2.0 separated by 6 sec of arc and revolving around each other in about 350 years. Each of these components has been found to be a spectroscopic binary. In addition, a faint companion, separated from the other two by 72 sec of arc, has been discovered. This star is also a spectroscopic binary, the two components of which revolve around each other in about one day. Hence, the entire system of the star Castor contains at least six stars. Its distance is about 45 light-years from the earth.