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Castor may also be part of a hugely extended, physically related, group of stars called the "Castor Moving Group" that includes Vega, Fomalhaut, Zubenelgenubi, and Alderamin.

Castor has no physical relation with Pollux, and at a distance of 51 light years (second Hipparcos reduction) is half again as far away as its mythological companion.

Castor B goes around Castor A (the brighter and more massive of the two, placed at the cross) with an orbital period of 445 years at an average separation of 100 Astronomical Units.

Each of the three is a spectroscopic double, making the system sextuple. How ironic that one of the "twins" should in fact be made of three sets of twins, Castor certainly the sky's ranking ...

The telescope reveals Castor's real claim to fame to be as a remarkable multiple star. Even a modest amateur instrument shows bright Castor to consist of a pair of similar stars only a few seconds of ...

To the naked eye, Castor shines down to us as a seemingly ordinary hydrogen-fusing class A star that appears much like Vega.

Castor and Pollux make a most attractive sight at the northern end of Gemini, Pollux an orange giant, Castor a contrasting white.

Castor's intimate mythological and celestial association with Pollux commonly sometimes lofts it into the "first magnitude" category, though in fact it is the brightest of the second magnitu ...

Though Castor is the fainter of the two, it still received the Alpha designation from Bayer, who made Pollux the Beta star.

CASTOR (Alpha Geminorum). In classical mythology, Castor is the mortal twin of Pollux, the twin warriors whose stars dominate the bright zodiacal constellation of Gemini.