Alpha Centauri is the closest star system beyond our own solar system, being 4.39 light-years away (about 25.8 trillion miles). The star Proxima Centauri, often regarded as part of the system, is only 4.26 light-years away from the Earth. 

This makes it a logical choice as "first port of call" for speculative fiction about space travel, which often assumes eventual human exploration of the system or even colonization of possible planets within it.  In the Star Trek: Enterprise episode "Future Tense", this system was the site of the Alpha Centauri colony - a founding member of the United Federation of Planets, along with Earth, Andoria, Tellar, and Vulcan.  In the Star Trek original series episode "Metamorphosis, the developer of the warp drive, Zefram Cochrane, is said to have lived in this system at one time.

Alpha Centauri is famous in the Southern Hemisphere as the outermost 'pointer' to the Southern Cross, but it is too far south to be visible in most of the northern hemisphere. 

The Southern Cross. Alpha Centauri is at the far left
and the dark patch in the middle of the cross is the Coalsack dark nebula .

Though it appears to the eye (and in the telescope) as a single point of light, it is a multiple system of three stars. Alpha Centauri A is one of very few bright stars that are a similar colour to the Sun and, indeed, is very similar to our own Sun, however, many speculate whether it might contain planets that harbour life. On February 25, 2008, simulations by a team of astronomers prouced results which support the conclusions of previous studies that multiple-planet systems could have formed in close orbits around both heavy-element rich, Alpha Centauri A and B. The simulations predicted an Earth-like planet in or near Star B's habitable zone (where liquid water could exist on the planet's surface).

The picture to the right illustrates the location of habitable zones in relation to the mass of the star and distance from it,