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Castor

Alpha Geminorum, 66 Geminorum

Proper NamesCastor
Bayer DesignationAlpha2,1 Geminorum, Alpha Geminorum A, B
Flamsteed Number66 Geminorum
BSC2891 (A), 2890 (B)
HD60179 (A), 60178 (B)
ConstellationGemini
Right Ascension7h 34m 36s
Declination+31° 53' 18"
Distance51 light years
16 parsecs
MagnitudeApparent: +1.6 (A), +2.9 (B)
Absolute: +0.6 (A), +1.9 (B)
Spectral ClassA1V White Main Sequence Star (A), A2Vm White Main Sequence Star (B)
Optimum VisibilityJanuary / February
NotesCastor is a multiple star system consisting of three close binary pairs. Two of these binaries, Castor A and Castor B, follow a relatively close orbit around one other, while the fainter variable binary Castor C pursues a more distant orbit around the primary pair.

A complex multiple star that shines brightly in the north of Gemini. Though designated 'Alpha', it is not the brightest star in its constellation: its magnitude is actually somewhat less than that of its mythical twin, Pollux.

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