Alpha Centauri is the brightest star in the southern constellation of Centaurus, and one of the brightest in the entire night sky. It is also one of the closest to us. It bears the proper name Rigil Kentaurus (often shortened to Rigil Kent), meaning "foot of the centaur", but is nonetheless usually referred to by its Bayer designation Alpha Centauri.
Alpha Centauri is in fact a double star. The larger component, Alpha Centauri A, is similar to the Sun, but a little larger and brighter. Like the sun, its spectral type is G2 V. The smaller component, Alpha Centauri B, is dimmer, with a spectral type of K1 V. The two orbit one another elliptically (e=0.52), approaching as close as 11.2 astronomical units and receding to 35.6 AU with a period of just under 80 years.
The red dwarf Proxima Centauri is only about 13,000 astronomical units away from Alpha Centauri and may be in orbit about it, with a period on the order of 500,000 years or more. For this reason, Proxima is sometimes referred to as Alpha Centauri C. However, it is not clear if it really is in orbit, although the association is unlikely to be entirely accidental it shares approximately the same motion through space as the larger star system.
Viewed from Alpha Centauri, the sky would appear very much as it does to us with most of the constellations such as Ursa Major and Orion being unchanged. However, Centaurus would be missing its brightest star and Cassiopeia would be home to a bright star in the form of Sol, our Sun.
There is also a videogame named Alpha Centauri.