- The sun pictured during the 2004 transit of Venus (yup, it’s the black dot at the top!)
On June 3rd 1769 Captain James Cook opened his ship´s log and noted:
“This day prov´d as favourable to our purpose as we could wish; not a Clowd was to be seen the whole day and the Air was perfectly clear”
The ‘purpose’ described by him was the primary reason for his voyage on board the Endeavour: to observe the transit of Venus. Also on board was the astronomer Charles Green, and they had gone to Tahiti on the instructions of George III to observe and measure the silhouette of the planet Venus as it crossed the face of the sun. Once they had completed their observation they were to head south in an endeavour to find the fabled ‘Unknown South Land’.
The astronomer Edmund Halley had been one of the people clamouring for the expedition. In 1716 he correctly predicted that observing and accurately recording the differences in the transit time, measured from two different places on the earth’s surface, would enable scientists to calculate the exact distance of the earth from the sun, and hence measure the size of the solar system. Halley called on the scientific community to combine forces so that accurate measurements could be taken all across the globe, knowing that the fairly straight-forward trigonometry calculation would give the measurement ‘to unlock the secrets of the universe’.
Halley correctly predicted the transit would next occur on June 6, 1761 and again on June 3, 1769. Ironically he never lived ot see either transit – just as he never lived to see the return of the comet which carries his name and whose trajectory he correctly calculated.
But the scientific community heeded his call, and a whole army of scientists embarked for distant places armed with stop watches and telescopes. The numbers they brought back were duly crunched and analyzed, and a conclusion was reached that the distance between the sun and the earth was in the range of 92,900,000 to 96,900,000 miles – very close to today’s figure of 92,960,000 miles.
The astronomical event occurs in pairs eight years apart, and then not again for another 105 years. It was last observed in 2004. This year is therefore the last chance any of us alive as adults today will see the occurrence, due on 5th/6th June 2012, as the next one will not come round until 11th December 2117 (and December 2125).
- Statue of Captain Cook at Gisborne, New Zealand
This year’s transit will be best viewed from the Pacific Ocean where it will be visible (cloud cover permitting) for most of the time. In Sydney the transit should start around 8.30 and last until 2.00 in the afternoon. The start of the transit will be visible in North America, and most of Europe will be able to observe the closing stages. Hard luck on the South Americas and those interested in astronomy in much of Africa – it will not be visible at all in those areas. In the United Kingdom the transit should be visible an hour after sunrise – at around 6 a.m.
In Australia plans are afoot to send a replica of the Endeavour to Lord Howe Island in June to repeat the earlier work of Captain Cook. The ballot to get on the crew list of 32 was drastically over-subscribed and each has to pay a substantial sum of money for the privilege of going on the voyage. Any ‘softy’ wanting the luxury of a cabin has had to fork out A$8000 For the rest of us, observing the event through smoked glass, or old X-ray film, is probably the best bet.
More information about the imminent transit can be found at:
And because the old maps are often so much more beautiful than their modern counterparts, here is Ferguson’s map showing the 1761 Transit: