Captain Cook and the Transit of Venus
James Cook sailed across the world to watch a small black dot cross the Sun from a Tahitian beach. He also carried secret orders.
What was reported
A transit of Venus, when the planet passes across the face of the Sun, happens twice in about eight years and then not for more than a century. By timing it from places far apart, astronomers hoped to measure the distance from the Earth to the Sun.
The Royal Society sent James Cook in the Endeavour to Tahiti to observe the transit of 3 June 1769, from a spot still called Point Venus. The observers were frustrated by the 'black drop', which blurred the moment Venus touched the edge of the Sun. Cook then opened sealed orders telling him to search the South Pacific for a great unknown southern continent.
Explanations offered
The black drop effect comes from blurring by the telescope and the atmosphere, and it made the timings less precise than hoped. Still, the results gave a reasonable estimate of the Earth–Sun distance. Cook's onward voyage reached New Zealand and eastern Australia.
- When
- 3 June 1769
- Where
- Point Venus, Tahiti, French Polynesia
- Witnesses
- The crew of the Endeavour
- Status
- Explained
Famous cases are real, widely reported events. Each file sets out what witnesses said and the explanations that have been offered, without taking a side.