According to NASA, this celestial event, dubbed the 'Transit of Venus'  is very rare and last occurred 129 years ago. It won’t happen again until December 2117. In fact, the event itself has only happened seven times since the telescope was even invented. Thanks to NASA, and their Ustream channel, we can see the event as it happens below. This is the Official Sun-Earth Day webcast for the Venus Transit brought to you live from the summit of Mauna Kea, Hawaii.

Streaming Live by Ustream