Alpha Comae Berenices (Alpha Com / 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 with a maximum separation of only 0.7 arcsec. It is not known whether eclipses occur between the two components at periastron (minimum separation)—the only such passage since the determination of the orbit, in 1990, was not quantitatively followed by observers.