In 1766, Captain Cook, the British explorer, was asked to sail to Tahiti with the ship Endeavour to observe and measure the Venus transit in 1769, three years later.
by Anne Mette Sannes
Captain James Cook
Photo: National Maritime Museum, United Kingdom
Captain Cooks perilous journey
Tahiti was discovered by the Europeans the year before, the whole area was so badly mapped, he might as well have gone to Mars. Without today's equipment, we had to set out to find the island which was only 30 kilometres wide. It was an extremely dangerous journey and Captain Cook expected to loose half of the crew on the way. But in spite of the threatening hazards, he still felt that observing a Venus transit was worth the risk. The goal was to get to the island in time, build an observatory and try to measure the size of the Solar System.
In 1761, Edmond Halley had realized that Venus was the key to the answer. Halley believed that by measuring the start- and stop times from various places, it would be possible to find the distance Earth – Venus by using the parallax principle. And when this was done, all the measures in the Solar System would follow. Halley himself would not live long enough to experience the Venus transit in 1761. If the expeditions failed, the next chance would not come until 1874.
The captain served his crew sauerkraut and some sort of malt wort and those who did not eat, were whipped. This happened to a fifth of the crew, about average at the time, according to sources.
When they reached Cape Horn after eight months, the expedition had lost five crew members and one had jumped over board. During the next ten weeks, they could not receive any weather forecasts or help of any kind. Instead, they navigated with hourglasses and knotted ropes to measure the speed, and a sextant and almanac to estimate the position by the stars – A tricky and very dangerous method.
Amazingly enough, the ship arrived in Tahiti in April 1769, two months before the Venus transit with the remaining crew in good health which captain Cook believed was due to the sauerkraut.
The island was beautiful and peaceful and the inhabitants were friendly. What more could they possibly want? The crew found the island so fabulous that the actual Venus transit on June 3rd seemed to pale in comparison and no one really talked much about the little black dot that made its way over the solar disk through their telescopes.
One of the crew members, Joseph Banks, an English naturalist and botanist, only wrote down 622 words on the day of the Venus transit, and unfortunately only 100 of these referred to the actual transit. Instead he wrote about the breakfast meeting with King Tarróa, about the kings sister and three other beautiful women who had arrived later in the day.
Cook himself wrote somewhat more and expressed that time before contact was disturbed by the atmosphere of Venus, in particular the to inner contact points. Because of this, the measurements made by Charles Green, one of the astronomers in the crew, deviated with Cooks own measurements with as much as 42 seconds.
Observations made by captain Cook and Charles Green. Note that the observations differ.
Photo/images:: Wikipedia / Captain James Cook and Charles Green
Both Cook and Green observed the black-drop-effect which also this time turned out to be a problem for observers around the world. Because of this, the results from all the 76 measurements were not accurate enough to estimate the size of the Solar System.
When the transit was over, captain Cook was ordered to look for a continent of major size located somewhere between Tahiti and New Zealand. But it turned out that Terra Australis, the unknown continent, did not exist, just as Cook had assumed. (It was found in 1820 by a Russian expedition and was named Antarktika.)
During a few weeks stay in Jakarta to make some repairs, seven of the crewmembers died of malaria. Cook decided to leave, but to late … 38 of the original crew died, including Charles Green. But Cook will always be remembered for his great concern for crew health.
The survivors who returned to England on June 11th 1771 had catalogued thousands of plants, insects and animals, met other people and searched for big continents.
The Venus transit was probably just a small part of captain Cooks experience, but still, after this great voyage of discovery, Cook and Venus will for ever be linked to each other. Cook became world famous because he was sent out to observe the Venus transit.
Captain Cooks transportable observatory.
Photo: Robert Benard, engraver
The ship HMS Endeavour outside the coast of New Holland
Painted by Samuel Atkins (c.1760-1810)
Major celestial events in Norway 2010-2015