On 12th August 1768, Captain James Cook and the crew of HMS Bark Endeavour, including a team of scientists, set sail from Plymouth Harbour to arrive at Tahiti the following year. Their aim: to observe the Transit of Venus in order to determine the distance between the Earth and the Sun.
Venus transits between the Earth and the Sun twice every 120 years or so. Scientists of the time realised it was one of the few ways in which they could calculate the distance between the Earth and the Sun, but the length of time in which each occurred was a problem. The next Transit would not be until 1874, and the last attempt to view the 1761 Transit had ended in failure, so this was the last chance for living scientists to view this important event.
The Endeavour arrived at Tahiti in April 1769, ample time to prepare for the Transit which occurred on 3rd June. After observing the Transit, Captain Cook and one of the ships’ astronomers, Charles Green, made detailed drawings of this spectacular event.
At the same time Captain Cook had observed the Transit, which had been fully visible in Tahiti, a North Yorkshire businessman and land-owner by the name of Ralph Jackson was doing exactly the same from England, from which the Transit had only been partially visible.
Ralph Jackson had kept a daily account of his life since he was 13, and he wrote in his journal on that day:
“[I]… observed (through my reflecting telescope), the Transit of Venus over the Sun’s Disk, she came on about four minutes after seven, & went down with the Sun.”