A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and Earth, becoming visible against (and hence obscuring a small portion of) the solar disk. During a transit, Venus can be seen from Earth as a small black disk moving across the face of the Sun.
Transits of Venus are among the rarest of predictable astronomical phenomena. They occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years. This month’s transit is the bookend of the 2004-2012 pair. The first occurred on June 8, 2004. This second one will occur on June 5, 2012.
After 2012, the next transits of Venus will be in December 2117 and December 2125.Image Credit: NASA