Claim: Alpha Centauri is a constellation.

Alpha Centauri -LRB- α Centauri , abbreviated Alpha Cen , α Cen -RRB- is the closest star system to the Solar System , being 4.37 ly from the Sun . It consists of three stars : the double star Alpha Centauri A -LRB- also named Rigil Kentaurus -RRB- and Alpha Centauri B together with a small and faint red dwarf , Alpha Centauri C -LRB- also named Proxima Centauri -RRB- , that may be gravitationally bound to the other two . To the unaided eye , the two main components appear as a single point of light with an apparent visual magnitude of − 0.27 , forming the brightest star in the southern constellation of Centaurus and is the third-brightest star in the night sky , outshone only by Sirius and Canopus .   Alpha Centauri A -LRB- α Cen A -RRB- has 1.1 times the mass and 1.519 times the luminosity of the Sun , while Alpha Centauri B -LRB- α Cen B -RRB- is smaller and cooler , at 0.907 times the Sun 's mass and 0.445 times its visual luminosity . During the pair 's 79.91-year orbit about a common centre , the distance between them varies from about that between Pluto and the Sun to that between Saturn and the Sun .   Proxima Centauri -LRB- α Cen C -RRB- is at the slightly smaller distance of 1.30 pc from the Sun , making it the closest star to the Sun , even though it is not visible to the naked eye . The separation of Proxima from Alpha Centauri AB is about 15000 AU , equivalent to 500 times the size of Neptune 's orbit . Proxima Centauri b , an Earth-sized exoplanet in the habitable zone of Proxima Centauri , has been detected .