Alpha is the brightest star in the constellation of the same name. It is also known as Alpha Centauri and is the third brightest star in the night sky. Alpha is a binary star system located in the Centaurus constellation, about 4.3 light-years from Earth. It is the closest star system to our own solar system and is composed of two stars, Alpha Centauri A and Alpha Centauri B. Alpha Centauri A is the brighter of the two stars and is about 1.2 times the mass of the Sun. Alpha Centauri B is slightly dimmer and is about 0.9 times the mass of the Sun.