Captain Cook and the Transit of Venus

Paul Brunton, as told to Echonetdaily

On 6 June we will be treated to an unusual astrological event – one that had an unlikely role in Captain Cook’s discovery of Australia’s east coast.

Cook was given the task of viewing the Transit of Venus on 3 June 1769 from a position in the South Pacific. The Transit had been first observed in 1639 and it did not occur again until 1761. The 1761 Transit observations had not been successful so it was important that accurate observations be made in 1769.

By observing the time Venus took to cross the face of the Sun from different parts of the Earth, scientists could calculate the distance of the Sun from the Earth. This was important information about the size of the solar system and also important for navigation at a time when latitude and longitude were calculated by the position of heavenly bodies. Cook viewed the Transit with a telescope.

It was particularly important that there be an observation in the southern hemisphere in order to compare with observations made in the northern hemisphere. However, when Cook was appointed it was not clear where this should be. The South Pacific was not charted much and what was charted was often inaccurately so, so that any island chosen might first have to be re-located before observations could begin.

Then in the nick of time Samuel Wallis returned to Britain on May 1768 from his circumnavigation. He had discovered Tahiti. Not only was this in the optimum geographical area for the observation but Wallis had precise latitude and longitude so that it could be located.

Some of Wallis’s crew said they had seen mountains to the south of Tahiti. Cook was given orders that after the observation he should sail south and see if he could find this land – thought to be the great southern continent that was believed to balance the land mass in the northern hemisphere otherwise the globe would topple over.

Cook did sail south and found no continent. He could then have gone home having fulfilled all his orders. But what made him great was that after circumnavigating New Zealand he decided not to go straight home but to sail west knowing that he must find the eastern coast of the land discovered by the Dutch (the west coast of Australia). He of course did this and charted the east coast, which was later chosen as the place for the first convict settlement – the beginning of the colonisation of Australia by the British.

So the Transit of Venus led directly to the colonisation of Australia. But it was a close thing. If Tahiti had not been discovered in the nick of time then Cook may not have been given his orders to seek the great southern continent, and if someone other than Cook had been chosen they may not have gone that extra mile and sought out the east coast of Australia. The convicts would have been sent somewhere else and Australian history would have been different. Perhaps we would have been settled by the French.

These chance occurrences are what I find so fascinating in this story. It is the great ‘what if’ of Australian history.

Lismore City Library is hosting a free talk on the Transit of Venus by Paul Brunton, senior curator of the Mitchell Library at the State Library of NSW. Learn how the Transit of Venus was instrumental in the discovery of Australia’s east coast by James Cook. View the original calculations in the hand of James Cook of the 1769 Transit of Venus. This talk will be held at the Goonellabah Community Centre tomorrow, 17 May, starting at 7:30 pm.

Watching the Transit

The Transit will occur on 6 June. It takes 6½ hours and scientists can be quite precise: it will begin at 8:16am and end at 2:44pm. It last occurred in 2004 but will not occur again for more than a hundred years. Two Transits usually occur eight years apart and then not again for more than a hundred years. The Transit before 2004 was 1882.

You should not look at the Transit with the naked eye or through a telescope, as this is dangerous to the eye. The Sydney Observatory website gives guidance on how to look at it safely.

Australia is one of the best places to view this Transit. Most of the northern hemisphere will be in darkness. Anywhere on Australia’s eastern coast is a very good vantage point as the Transit will occur completely in daylight hours.


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