The transit of Venus is one of the rarest astronomical events in our solar system. It happens in pairs, every century. This awe-inspiring video shows the first of this century's pair, which happened in 2004. The next one is about to happen—on June 5, 2012.
NASA is going to webcast it from atop the summit of Mauna Kea, Hawaii. Be sure to watch it because the next one is not happening till 2117. [NASA and NASA Goddard Flickr]
Update: If you are in NYC, you can also watch it at the Rose Center for Earth and Space, in the hall of the universe, on the astrobulletin—the giant screen downstairs.