A transit of Venus takes place when the planet Venus passes directly between the Earth and the Sun. A transit is similar to a solar eclipse by our own Moon. However, although Venus is much larger than our Moon, it is also far more distant, so it only covers a tiny portion of the Sun.
A transit of Venus is a very rare event which occurs in pairs which are eight years apart, the time between these pairs of transits is however 121.5 and 105.5 years !
The previous pair of transits before 2004 happened in the year 1874 and 1882.
The next transits of Venus will take place on 10–11 December 2117, and 8 December 2125