triple star, the faintest component of which, Proxima Centauri, is the closest star to the Sun, at about 4.2 light-years' distance. The two brighter components, about ¹/₅ light-year farther from the Sun, revolve around each other with a period of about 80 years, while Proxima circles them with a period probably of millions of years. The brightest component star resembles the Sun in spectral type, diameter, and absolute magnitude. Its apparent visual magnitude is 0.0. The second brightest component, of visual magnitude 1.4, is a redder star. The third component, of 11th magnitude, is a red dwarf star.

As seen from Earth, the system is the fourth brightest star (after Sirius, Canopus, and Arcturus); the red dwarf Proxima is invisible to the unaided eye. Alpha Centauri can be seen only from south of about 40° north latitude.