Alpha Centauri main sequence star. Animation of the location in the night sky and the properties of the yellow G-type star Alpha Centauri A (also called Rigil Kentaurus), 4.37 light years from Earth in the constellation of Centaurus. Alpha Centauri A is a main sequence star, 1.23 times the width of the Sun (over 1.7 million kilometres across) and 1.1 times the Sun's mass. Alpha Centauri A is very similar to the Sun, and with its companion stars (the binary companion Alpha Centauri B and the more distant Alpha Centauri C) forms the closest star system to Earth. Alpha Centauri A is thought to be 6 to 7 billion years old, and like the Sun will shine for several more billion years. Alpha Centauri A is spectral type G2, with a luminosity class of V. It has a luminosity 1.519 times that of the Sun, and has an atmospheric temperature of 5790 Kelvin. Its spectrum has neutral and ionized metal lines, especially ionized calcium lines.