Transit of Venus: What is it and who can see it?
6 June 2012 Last updated at 06:18 BST
The transit of Venus, where the planet Venus passes directly between the Earth and the Sun, will begin at 2204GMT/2304BST on Tuesday 5 June and will end at 0455GMT/0555BST.
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. She also explains which parts of the world will be able to see the 2012 transit.
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