| Castor (Alpha Geminorum; a Gem) |
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The second-brightest star in the constellation Gemini, after Pollux. Its magnitude as seen by the naked eye is 1.6, but this is the combined brightness of a multiple system with at least six components. There are two A stars of magnitudes 2.0 and 2.9 forming a close visual pair, each of which is a spectroscopic binary, and a more distant ninth magnitude red star, which is an eclipsing binary. See also: Table 3. |