Transit of Venus: What is it and why is it so rare?
2 June 2012 Last updated at 00:50 BST
The transit of Venus, where the planet Venus passes directly between the Earth and the Sun, will begin just a few minutes after 22:00 GMT (23:00 BST) on Tuesday 5 June and will end just before 04:55GMT (05:55 BST) on Wednesday 6 June.
As it happens, Venus appears as a small black dot moving across the surface of the Sun.
Here, science presenter Liz Bonnin explains how the transit works and why it is such a rare event - the next one will not happen until 2117.
Experts warn never to look directly at the Sun without special eclipse glasses, and not to view it through binoculars or a telescope, which could result in serious injury or blindness