Star
Castor
White star · A2Vm
α Geminorum · Gemini
Shown in its true colour — like most stars, it is too far away to photograph as more than a point of light.
Castor is the second-brightest object in the zodiac constellation of Gemini. It has the Bayer designation α Geminorum, which is Latinised to Alpha Geminorum and abbreviated Alpha Gem or α Gem. With an apparent visual magnitude of 1.58, it is one of the brightest stars in the night sky. Castor appears singular to the naked eye, but it is actually a sextuple star system organized into three binary pairs. Although it is the 'α' (alpha) member of the constellation, it is half a magnitude fainter than 'β' (beta) Geminorum, Pollux.
Description from Wikipedia (CC BY-SA 4.0).
In your sky
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Key facts
Distance
~50.9 light-years
Apparent mag.
+1.58
Spectral type
A2Vm
Luminosity
49.4 × Sun
Absolute mag.
+0.61
Catalogue
HIP 36850
Spectral type
A2Vm
True colour from its B–V index (0.03): a surface around 9800 K.
Did you know
- Castor is also known as α Geminorum.
- Its spectral type A2Vm marks it as a white star.
- It lies in the constellation Gemini.
