Monthly Archives: June 2012

THE TRANSIT OF VENUS AND JAMES COOK

As you’ve no doubt noticed in the news, the planet Venus has just made one of its rare transits across the sun, something it does every 120 years or so, when it then does it twice in eight years for good measure.

Back in 1768, Britain’s Royal Academy sponsored a bold trip to Tahiti  on the other side of the world to observe the transit and, from this, try to measure the scale of the solar system. Over six dozen observations from other points of the earth were also made, by a range of European powers.

The bloke they entrusted with this particular trip was Lieutenant James Cook, who had already distinguished himself in navigation, cartography and even war. With him went a young scientific toff, Joseph Banks.

Off they went across thousands of sea miles, to an area of the globe that was barely known or mapped, without satellite photos, GPS, speed gauges or even a very accurate clock to measure longitude (i.e. how far east or west they were), to try and land on a small island in the South Pacific discovered by Europeans only the year before.

Point Venus, from which Cook observed the transit

Once there, they were to establish rapport with the natives and set up a small observatory. Afterwards, they were to search for evidence of the fabled Unknown South Land which, so some believed, must exist to act as a counter-weight to all that land in the Northern Hemisphere.

To prevent his crew dying of scurvy, Cook insisted they eat vegies like sauerkraut and malt wort, on pain of a flogging. The same punishment applied to any jack on watch who forgot to wind up the ship’s chronometer. Cook was not shy about use of the lash, deploying it even more than Captain Bligh (who was to become master of a ship on Cook’s last voyage).

The Endeavour replica, which has just completed its own epic voyage.

Cook’s ship Endeavour arrived in Tahiti in mid 1769 and the islanders made the Britishers welcome. After the long voyage and with the novelty of their surrounds, both Cook and Banks recorded more about Tahitian matters than about Venus when she glided across the sun on 3rd June. Banks barely bothered to look at it, being preoccupied with local pals. Cook was more dutiful, recording “not a Clowd was to be seen… and the Air was perfectly clear, so that we had every advantage… in Observing the whole of the passage of the Planet Venus over the Suns disk.”

In the long run, unfortunately his and other people’s measurements were not precise enough to estimate the size of the solar system; this was not achieved until photography was available.

With this job done Endeavour proceeded to search rather randomly for the great south land, including pushing south into ice-packed seas. It then headed west; to read more about its travels thereafter, key “endeavour” into the search window at top right.

[For info in this blog, I’m indebted to NASA, Jim Cook and Joe Banks.]