Castor

Set at a northern declination of +31° within the constellation Gemini, Castor marks one head of the celestial twins beside brighter Pollux. Designated Alpha Geminorum, it is a white A-type star with a nearly neutral B–V index of 0.034 and shines at apparent magnitude 1.58. The star lies about 51 light-years away, and its absolute magnitude of 0.62 reflects an intrinsic brightness moderately above the Sun's. Although labelled Alpha, Castor is slightly fainter than Beta Pollux, an ordering fixed by tradition rather than brightness. Its high northern position keeps it prominent in the winter evening sky.