Irish stargazers seeking Venus

Event lasts about 6 hours UK timing: 0620-1224 BST Viewing must use protection Web and TV is safest option

Amateur astronomers are set to gather in Belfast to watch a very rare passage of Venus across the face of the Sun.

Special equipment is being erected in Botanic Gardens for the public to see the phenomenon.

Tuesday will be the first time for 122 years that the whole event will be visible from Ireland.

No person alive has ever seen a 'Transit of Venus'.

Terry Moseley of the Irish Astronomical Association said because Venus's path is slightly tilted, it normally passes just above or below the Sun on each orbit.

"But sometimes it lines up just right, and we see it as a black spot slowly crossing the disc of the Sun," he said.

"These events occur in pairs about eight years apart, but with each pair separated by well over a century.

"The last one was in 1882, and the next will be on 6 June 2012, and the one after that won't occur until December 2117."

The association will be setting up special telescopes and safety equipment for the public to observe the transit.

They will be available to use in Botanic Gardens, near the Ulster Museum, Stranmillis Road from about 0830 BST until the end of the event.

The planet will soon be visited by Europe's Venus Express probe

"All the equipment we have has been tested to be absolutely safe, and has been used to observe the Sun many times before," said Mr Moseley.

"Members of the public coming to the event are requested not to bring their own telescopes or binoculars, just in case they are tempted to have a quick look - with awful consequences."

Organisers will be able to view a CD about Venus and there will be an internet link-up so the transit can be seen from clearer skies if it is too cloudy.

Observers will position themselves in Europe, Asia and Africa to get the best view the six-hour transit.

Scientists will use the event to test technologies they will soon deploy to detect similar sized worlds orbiting stars tens of light-years away.

Stream pictures

Venus will appear as a tiny black disc against our star, but no one should look for it without the proper equipment.

Looking directly at the Sun with the naked eye, and worse still through an open telescope or binoculars, can result in blindness.

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It is recommended people attend an organised viewing where the transit will be projected on to a screen; or they can visit one of the many institutional internet sites planning to stream pictures.

The latter may be the very best option, especially if the local weather is cloudy - something UK skywatchers know only to well.

But this is an event that should be caught in some fashion.

There have only been six transits in the telescopic age - in 1631, 1639, 1761, 1769, 1874 and 1882.