It is in a system about 16 light-years away from earth.
The location was never revealed in the orginial series. The only reference was Scotty's line in The Motion Picture that the Enterprise could have Spock back on Vulan in 4 days. Since then, several of the books named Vulcan's parent star as 40 Eridani A which apparently Gene Roddenberry liked. The first reference to the actual distance was in the fourth season of Enterprise where Trip says that Vulcan is 16 light-years from Earth.
40 Eridani is a triple star system about 16.5 light-years from Earth. However, this does not mean that Vulcan's solar system has three stars at the center. The two companion stars are white dwarfs that orbit 40 Eridani A at a distance of 400 Astromical Units. By comparison, Pluto's orbit takes it about 48 AU from our sun. The companion stars would be visible in the daytime, but would not be bright enough at night to diminish the darkness. Instead they would appear as white and orange stars.
Vulcan's sun, 40 Eridani A, is orange main sequence star, spectral class K which means that it is slightly smaller than our sun. These types of stars are more common than our yellow main sequence star and are the primary focus for the search for alien life. The habitable zone for 40 Eridani A has been caclulated to be about .6 AU. (Venus is about .7 AU from the sun.) So there may actually be a real planet orbiting this star. Admiral William Thomas Riker 22:02, July 26, 2011 (UTC)