On June 5th/6th(depending on timezone) Venus will pass directly between the Sun and Earth, becoming visible against the sun. The last transit took place on 8 June 2004. After 2012, the next transits of Venus will be in December 2117 and December 2125.
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.
I plan on doing a high dose of pharmahuasca to celebrate this twice in a lifetime event(or once if you missed it in 2004 like me). If you're interested in watching it take place you can find more info & where/when its visible here:
http://www.transitofvenus.org/
This is an image of the 2004 transit:
