Earth, Venus and the sun will align on Tuesday in a rare astronomical event that won’t be repeated for more than a century.
During the so-called “transit of Venus,” which is similar to a solar eclipse by the moon, the planet passes directly between the sun and Earth and becomes visible as a small dot drifting across the sun.
The more than six-and-a-half-hour transit, which starts just after 22:00 GMT (23:00 BST) on Tuesday is a very rare astronomical phenomenon that will not be witnessed again until 2117.
The transit will be best viewed from the Pacific region but it will also be visible from Britain just after sunrise on Wednesday.
Looking directly at the Sun with the naked eye, or worse still through an open telescope or binoculars, can result in serious injury and even blindness.
It is recommended people attend an organised viewing event where the transit will be projected on to a screen; The NASA will webcast it from the summit of Mauna Kea volcano in Hawaii.
Physics professor Peter Garnavich said the transit is one of the rarest events of the solar system. ‘Venus has passed directly between the Earth and Sun only 52 times between 2000 BC and 2000 AD,’ he pointed out.
‘There have only been seven Venus transits since the invention of the telescope in the early 1600s. At the start of the transit of 1761, a ring of light was seen around the disc of Venus and it was realised that the planet must have an atmosphere.’
Nasa’s Kepler mission now uses the same technique to search for planets outside the solar system – as distant planets cross a star, they temporarily dim its light.
Mr Garnavich said: ‘At the time of the Venus transit of 1882, there were eight known planets, all in orbit around the Sun. For the transit of 2012, there are more than 700 catalogued planets, many discovered by their transit across the face of their stars by the Kepler satellite.’
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