Alpha Centauri

The closest star system to the Sun, at a distance of more than four light-years, Alpha Centauri consists of three stars. Two of the stars -- one of which is similar to the Sun, while the other is a little smaller and cooler -- form a tight pairing. The third, known as Proxima Centauri, is about one-tenth of a light-year from the other two, and is a red dwarf star. It is closer to Earth than the other two stars, but it is so faint that it is not visible to the unaided eye.