It is the third brightest star in the night sky on Earth, after Sirius and Canopus. Although it appears to the unaided eye as a single object, Alpha Centauri is actually a binary star system (designated Alpha Centauri AB or α Cen AB). Alpha Centauri is located 1.34 parsecs or 4.37 light-years from the Sun, making it the closest star system to the Sol System.
Its component stars are named Alpha Centauri A (α Cen A), with 110% of the mass and 151.9% the luminosity of the Sun, and Alpha Centauri B (α Cen B), at 90.7% of the Sun's mass and 44.5% of its luminosity. During the pair's 79.91-year orbit about a common center, the distance between them varies from about that between Pluto and the Sun to that between Saturn and the Sun.
Around the larger of the two stars Alpha Centauri A, or Alpha, was the human settlement of Alpha.