In the early 17th Century Johannes Kepler calculated the distances of each planet from the sun relative to the distance of Earth from the sun, but no one had been able to calculate what that actual distance was. An early estimate was 59 million miles, which is only 2/3rds of the actual distance.
Due to the path of Venus’ orbit that planet is occasionally seen to pass (or transit) in front of the sun. Such transits occur in pairs eight years apart, with an interval of over 100 years between the pairs. For example, transits over the last 200 years were in December 1874, December 1882, June 2004 and June 2012, with the next to occur in December 2117 and December 2125.
In 1716 Edmund Halley (of the comet fame) suggested that accurate measurements of the time taken for the transit of the planet Venus that was to happen in 1761 would allow a calculation of the distance from the sun to be made.
A photograph taken during the 2012 transit of Venus
Although Halley died in 1742 over 100 teams of astronomers followed his advice and travelled to different parts of the Earth in 1761 to take measurements. The results were inconclusive due to misadventures and poor weather, so astronomers were keen to try again at the next transit. This would happen on 3 June 1769 and England’s Royal Society was keen “to undertake an observation of the transit of Venus from an island in the South Seas.” With Royal and government backing an expedition was organised to travel to the newly discovered island of Tahiti. Lieutenant James Cook was appointed commander and he sailed from England in the Endeavour on 26 August 1768.
Replica of the Endeavour
Cook arrived in Matavai Bay in Tahiti on 13 April 1769, giving seven weeks to prepare for the transit on 3 June. He built a fort on the northern point of the bay and set up an observatory. The fort was called Fort Venus and the point became known as Point Venus.
A chart of Matavai Bay drawn by James Cook in 1769
On Saturday 3 June Cook sent two other parties out to observe. One went to an islet to the east of Tahiti and his second in command John Gore rowed west to Moorea. Cook wrote, “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, so that we had every advantage we could desire in Observing the whole of the passage of the Planet Venus over the Suns disk: we very distinctly saw an Atmosphere or dusky shade round the body of the Planet which very much disturbed the times of the contacts particularly the two internal ones. Dr Solander observed as well as Mr Green and my self, and we differ’d from one another in observeing the times of the Contacts much more than could be expected — Mr Greens Telescope and mine where of the same Magifying power but that of the Dr was greater than ours- It was nerly calm the whole day and the Thermometer expose’d to the Sun about the middle of the Day rose to a degree of heat we have not before met with, 119°.”
The measurements made again were disappointing and Cook believed he had failed. However, the measurements from all the observation sites were combined in 1771 and a mean distance from Earth to the sun of 93,726,900 miles was calculated. This is within 1% of the currently accepted distance of 92,955,000 miles (149,597,000 km.)
Point Venus has changed a lot since 1769. The river (the Vaipopo) that flowed through it to the ocean when Cook was here has a new course now and its flow is much reduced.
Tahitian fishing canoes pulled up on Point Venus. Moorea in the background
From the black sand of Point Venus across the bay to what Cook labelled “One Tree Hill” (see chart above)
To get to Point Venus now you turn off the main road at the VenuStar supermarket, which is about 10 km east of Papeete. There is a roundabout here, which helps one negotiate the traffic. The car park is about 1.5 km further at the end of a narrow road. We went to the end of the point and there were four stingrays swimming in the shallows there, hoping for food. We crossed over to the black sand beach (Plage de la Pointe Vénus) with its great view over Matavai Bay to Papeete and further to Moorea.
Looking from Point Venus across Matavai Bay to Papeete, with Moorea in the distance
There is a monument to Cook’s first visit on the Point, as well as ones to the Bounty, here in 1788 – 1789, and the first LMS missionaries to bring Christianity to French Polynesia in the 19th Century.
The monument commemorating James Cook’s first visit to Tahiti
Detail from the plaque on the above monument
The Bounty monument. As some commentators have suggested, this seems to be more based on Hollywood movies than on history
Plaque on memorial to the first Christian missionaries
A lighthouse was built on the point in 1867, although it is now abandoned.
Lighthouse on Point Venus
As great admirer of James Cook, Peter found this a very fascinating place to visit and we were glad that we had been able to find it on our Tahiti circumnavigation.