Alpha Centauri << AL fuh sehn TAWR eye >> is a multiple star system in the constellation Centaurus. It is an extremely bright star system that astronomers classify as a zero magnitude system (see Star (Brightness of stars) ). It can be seen from the Southern Hemisphere and just north of the equator. It consists of Centauri A, a –0.01 magnitude yellow star similar to the sun, and the smaller 1.33 magnitude orange star Centauri B. These two stars make up a binary star (pair of stars) that orbit each other every 80 years (see Binary star ). About 0.1 light-year away is Proxima Centauri , a magnitude 11 small reddish star. One light-year equals the distance light travels in a vacuum in a year, about 9.46 trillion kilometers. Proxima is the closest star to Earth besides the sun. Many astronomers believe Proxima Centauri orbits Centauri A and B about once every 1 million years. This orbit would make Alpha Centauri a triple star system. Centauri A and B are 4.3 light-years from Earth. Proxima is 4.2 light-years from Earth. Alpha Centauri is approaching Earth at 12 miles (23 kilometers) per second. In 2016, astronomers announced evidence of a roughly Earth-sized planet orbiting Proxima Centauri within its habitable zone, the region around a star in which liquid water could exist on a planet’s surface.
