Astronomically, the two brightest stars in this region (Gemini) are Castor and Pollux, the heads of the two interlocked brothers. According to legend, these were twins born of Queen Leda of Sparta […] Although Castor and Pollux appear close to each other in the sky and are of similar brightness, they are really separated by several million miles. Pollux, an orange giant, is some thirty-six light years from the Earth, while Castor, which appears to be blue-white in colour, is forty-five light years away. In fact, Castor is an amazingly complex object.

Sheila Gilhaney: little Book of Stars.