Date: June 6   Time: 5:17

The Transit of Venus is one of the rarest sights in astronomy, it occurs when the planet Venus passes in front of the Sun and blocks out a small area of the Sun’s surface. The pattern that it follows repeats every 243 years, with pairs of transits eight years apart, separated by long gaps of 105.5 and 121.5 years.

The first person to watch the transit of Venus was English astronomer Jeremiah Horrocks in 1639. He estimated the distance between the Earth and the Sun to be roughly ⅔ of its real distance, a much more accurate prediction than any other at that time. His viewing of the transit increased public interest dramatically, so for the next pair of transits (in 1761 and 1769) numerous expeditions were made, including Captain James Cook’s first expedition. The aim of these various voyages was to collect as many readings as possible from different parts of the world to calculate the size of the solar system with precision. Using the observations from the 1761 and 1769 transits, the distance from the Earth to the Sun was estimated as being 153 million km, extremely close to the actual figure of 149.5 million. The correct figure was then calculated from the results of the transits of 1874 and 1882.

There was a great deal of interest in the transit of 2004. The same technologies that could help to find planets outside our Solar System were used to spot Venus moving across the Sun. Scientists hoped that by measuring the tiny dimming of the Sun’s light, they could similarly measure other stars to see if a dimming was also seen there, this would help to see if smaller planets existed in faraway Solar Systems. This was also the first transit that came after the invention of mass media, it was available to watch live online! The 2004 transit was by far the most watched in history.

On the 5/6 th of June 2012 (depending on your region) the small black dot of Venus will once again appear and travel slowly across the Sun. Whether you will stay put in Ireland to catch the end, travel to see it all or just watch the whole thing online (the NASA live video is streamed from Hawaii, find it here), the 2012 transit of Venus will definitely be a event to remember. In Ireland we will only catch the end of the event as the Sun rises at 5:17am (not for morning people) with the transit already underway. You can be sure though that this will be one of the busiest dawns you’ll ever see, so get together with family, friends or fellow skywatchers and marvel together at the wonders of nature, just remember suitable eye protection!

Written by Liam Coates, TY Work Placement

UPDATE: Terry Moseley has written an excellent article about the best place in Ireland to view the transit of Venus. Bad news- it isn’t Cork!