Alpha Comae Berenices

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This article is about the star called Diadem, for alternate meanings see Diadem.

Alpha Comae Berenices (α Com / α Comae Berenices) is a star in the constellation Coma Berenices (Berenice's Hair). Although it has the Bayer designation "alpha", at magnitude 4.32 it is actually fainter than Beta Comae Berenices. It also has the traditional name Diadem. It is said to represent the crown worn by Queen Berenice.

It is a binary star, with almost equal components of magnitudes 5.05m and 5.08m orbiting each other with a period of 25.87 years. The system, estimated to be 65 light years distant, appears so nearly "edge-on" from the Earth that the two stars appear to move back-and-forth in a straight line, but it is not an eclipsing binary. The mean separation between them is approximately 10 A.U., about the distance between the sun and Saturn.