THE world went Venus-crazy on 8 June, when the second rock from the sun could briefly be seen passing across the solar surface.
Visible from most of Europe, Africa and Asia, the 6-hour transit was tipped as a not-to-be-missed astronomical event, as only two occur roughly every century. Scientifically, it told us little that we didn鈥檛 already know, but it did provide a salutary reminder of the titanic efforts that were needed a few centuries ago to establish what we now take for granted.
By measuring the position of the transiting Venus from different places on Earth, scientists could work out the planet鈥檚 distance, and using Kepler鈥檚 laws of planetary motion, they could then work out the distances of all the planets from the sun. For the 1761 transit, for instance, a pair of English scientists embarked on a voyage to Sumatra to measure the position of Venus on the solar disc. But they were caught in Anglo-French crossfire from the Seven Years War. One Frenchman aiming to measure the same transit from India met with such a catalogue of mishaps that he didn鈥檛 return home for more than a decade. An epidemic of typhus killed a French astronomer shortly after he successfully measured the 1769 transit in Baja California.
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Fortunately there were other transit expeditions, such as Captain James Cook鈥檚 to newly discovered Tahiti in 1769, that went beautifully to plan. Eventually they allowed scientists of the day to calculate the distance between the Earth and the sun to an accuracy of 1 per cent.
If you missed the 2004 Venus transit, your next opportunity will be on 6 June 2012, when the ringside seats will be in east Asia, the Pacific and the north-western US. Miss that and you鈥檝e had it. The next one won鈥檛 occur until 10 December 2117.
