Transits of Venus

But there was a problem. Transits of Venus are rare. They come in pairs, 8 years apart, separated by approximately 120 years. Halley himself would never live to see one. An international team did try to time a Venus transit in 1761, but weather and other factors spoiled most of their data. If Cook and others failed in 1769, every astronomer on Earth would be dead before the next opportunity in 1874.

Credit: National Library of Australia Portrait of Cook, oil on canvas, Nathanial Dance, 1735-1811.

Cook's expedition is often likened to a space mission. "The Endeavour was not only on a voyage of discovery," writes Tony Horwitz in the Cook travelogue Blue Latitudes, "it was also a laboratory for testing the latest theories and technologies, much as spaceships are today."

In particular, the crew of the Endeavour were to be guinea pigs in the Navy's fight against "the scourge of the sea" - scurvy. The human body can store only about 6 week's worth of vitamin C, and when it runs out seamen experience lassitude, rotted gums, haemorrhaging. Some 18th century ships lost half their crew to scurvy. Cook carried a variety of experimental foods onboard, feeding his crew such things as sauerkraut and malt wort. Anyone who refused the fare would be whipped. Indeed, Cook flogged one in five of his crew, about average in those days, according to Horwitz.

By the time Cook reached Tahiti in 1769, he'd been sailing west for 8 months - about as long as modern astronauts would spend en route to Mars. Five crewmen were lost when the ship rounded stormy Cape Horn, and another despairing marine threw himself overboard during the 10-week Pacific passage that followed. The Endeavour was utterly vulnerable as it angled toward Tahiti. There was no contact with "Mission Control," no satellite weather images to warn of approaching storms, no help of any kind. Cook navigated using hourglasses and knotted ropes to measure ship's speed, and a sextant and almanac to estimate Endeavour's position by the stars. It was tricky and dangerous.

Remarkably, they arrived mostly intact on April 13th, 1769, almost two months before the transit. "At this time we had but very few men upon the Sick list … the Ships company had in general been very healthy owing in a great measure to the Sour krout," wrote Cook.

Tahiti was as alien to Cook's men as Mars might seem to us today. No spacesuit was required to survive. On the contrary, the island was comfortable and well provisioned for human life; the islanders were friendly and eager to deal with Cook's men. Banks deemed it "the truest picture of an arcadia (idyllic and peaceful) … that the imagination can form." Yet the flora, fauna, customs and habits of Tahiti were shockingly different from those of England; Endeavour's crew was absorbed, amazed.