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Alpha Centauri is a gravitationally bound system of the closest stars and planets to the Solar System at 4.37 light-years from the Sun. The name is Latinized from α Centauri, and abbreviated Alpha Cen or α Cen. It is a triple star system consisting of α Centauri A , α Centauri B , and the closest star α Centauri C.
Alpha Centauri A and B are Sun-like stars , and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.
Alpha Centauri A has 1.1 times the mass and 1.5 times the luminosity of the Sun, while Alpha Centauri B is smaller and cooler, at 0.9 times the Sun's mass and less than 0.5 times its luminosity. The pair orbit around a common centre with an orbital period of 79 years. Their elliptical orbit is eccentric, so that the distance between A and B varies from 35.6 A.U. , or about the distance between Pluto and the Sun, to 11.2 A.U., or about the distance between Saturn and the Sun.
Alpha Centauri C, or Proxima Centauri, is a small faint red dwarf. Though not visible to the naked eye, Proxima Centauri is the closest star to the Sun at a distance of 4.24 ly , slightly closer than Alpha Centauri AB. Currently, the distance between Proxima Centauri and Alpha Centauri AB is about 13,000 AU , equivalent to about 430 times the radius of Neptune's orbit.