Regulus main sequence star. Animation of the location in the night sky and the properties of the blue-white B-type star Regulus A (Alpha Leonis), 79 light years from Earth in the constellation of Leo. Regulus A is a main sequence star, 3.1 times the width of the Sun (over 4.3 million kilometres across) and 3.8 times the Sun's mass. Regulus A is one of the brightest stars in the sky. It is a few hundred million years old and has a binary companion Regulus B that is thought to have transferred mass to it, leading to a very high rotation speed for Regulus A. Regulus A is spectral type B7, with a luminosity class of V. It has a luminosity 288 times that of the Sun, and has an atmospheric temperature of 12, 460 Kelvin. Its spectrum has moderate hydrogen lines and prominent helium lines.