Images of the Venus transit 8th June 2004
Conjunction of Venus with Jupiter March 2012
Because Venus lies between the Earth and the Sun, it shows phases, just like the Moon. Just like the Moon, too, it will transit across the face of the Sun. Unlike the Moon, Venus is not big enough to eclipse the Sun, but it is big enough to be seen in transit. Because the orbit of Venus is inclined to that of the Earth, it does not transit the Sun every time it passes between the Earth and the Sun. Venus transits happen in pairs, eight years apart, with just over a hundred years between the pairs. So the last one prior to 2004 was in December 1882. The next one will be in 2012, and not for British viewers. Prior to 2004 only six transits had occured since the development of the telescope. The first to be observed telescopically was also the first to be predicted, in 1639, by an English clergyman and astronomer Jeremiah Horrocks. It was observed by just two people - Horrocks himself and his colleague William Crabtree.
During the eightennth and nineteenth centuries timings of the transits of Venus across the face of the Sun from various points on the Earth gave us our first accurate measurements of the distance between Sun and Earth. Scientific bodies from all the major nations sent expeditions to far flung corners of the earth to time the four transits. Captain James Cook was one of those involved. Major discoveries were made as a result of some of these expeditions, but others are tales of misfortune and years spent away from home.
The 2004 transit did not have the same scientific interest - it was instead a people's transit, and the people watched in their thousands. Anybody could go along to an organised observing event, or just wander into an astronomer's garden. It was widely covered, and well covered, by the media. No-one alive had seen a transit of Venus prior to this one. For most of us, it was a once in a lifetime event.
And the British weather? This time it played along. I had the last few minutes clouded out. I saw third contact but not fourth. I watched from my garden, projecting the image through a 60mm telescope stopped down to 40mm, sitting in the sun between observations and showing it off to anybody who happened to walk past. I hadn't expected to find it very interesting - watching a little black thing crawl across the face of the Sun. I started watching out of a sense of duty, and found it enthralling.