Alpha Centauri, AL fuh sehn TAWR eye, is a multiple star system in the constellation Centaurus. It is visible from only the Southern Hemisphere. It consists of three stars that differ in brightness. One of them is Proxima Centauri, the star closest to Earth, except for the sun. This star lies 4.2 light-years away (see Light-year). The other two stars, Alpha Centauri A and Alpha Centauri B, are a binary system, a pair of closely spaced stars that orbit each other (see Binary star). They are about 4.4 light-years from Earth. The brightest of the three stars is Alpha Centauri A, which has an apparent magnitude of 0.01. The apparent magnitude of Alpha Centauri B is 1.34, and Proxima Centauri's apparent magnitude is 11.09 (see Star). Alpha Centauri is approaching our solar system at about 14 miles (23 kilometers) per second.