Unless you plan on living another 115 years, tonight is your last chance to see one of the most magical astronomical sights: the planet Venus passing across the face of the Sun. As she makes her slow progress--beginning at just after 11pm UK time and ending just after sunrise tomorrow morning--amateur astronomers around the world will be watching. Even the Hubble Telescope is in on the action--using the Moon as a mirror to take readings.
But while it's fun to think that on, say, December 13 2611 we can accurately predict that a transit will be occurring, looking back at past transits is even more vertiginous.
Transits have been observed since 1639, when a man named Jeremiah Horrocks--a virtual unknown to the scientific community--worked out the timings and projected a little image of the Sun onto his wall, with that distinctive little black dot in view. By the time of the next transit in 1761, the world was waiting, and particularly good observations were made by two of the great names in international science: Charles Mason and Jeremiah Dixon.
But 1769 saw the most elaborate expeditions yet, when a young Lieutenant named James Cook was charged with the task of taking observations at Tahiti. Cook's voyage can teach us much about the way astronomy and geopolitics have intersected. When he arrived on the island Cook immediately set up an observation station that looks more like a high-security prison than anything else. Yet even that wasn't enough to prevent his magnificent quadrant--a vital piece of kit--being stolen. To retrieve it, local chiefs were taken hostage; an extreme measure, but nothing compared to Cook's retaliation ten years later when, on the same island, another instrument was stolen and the thief's ears were cut off in punishment.
The lasting legacy of Cook's first voyage, however, was not the tale of theft and fortification, nor was it the records of the transit that were said by his backers, the Royal Society, to be so important. Rather it was the path of the voyage itself. For Cook and his men became the first westerners to chart the south-east coast of Australia. It is not so much that the transit was a 'cover' for colonial adventure--rather that astronomy and geography were then intertwined with the politics of discovery. Within 20 years there were British settlements in what Cook named 'New South Wales', and by the time of the next transit in 1874 its state capital, Sydney, had a population of over well over 100,000.
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