The transit of Venus

The forthcoming transit of Venus (on 5-6 June 2012) is an opportunity to remind ourselves how the needs of society determine the development of science. Venus passes in front of the Sun on two occasions about 8 years apart about once in every century. Soon after Johannes Kepler had formulated his third law - that a planet's distance is proportional to the time to complete on orbit - in 1609, it was realized that the transit of Venus can be used to determine the distance between the Earth and the Sun, which in turn can be used to determine longitude, a task of vital importance to open ocean navigation. It was the time of and colonial acquisition, and imperial powers had a great interest in this. Their interest was so great indeed that Britain, France and Austria cooperated in sending science parties out to Siberia, Norway, Newfoundland and Madagascar to observe the transit of Venus of 1761. Unfortunately clouds prevented most observers from getting good data, but a second chance came 8 years later. So in 1768 Britain sent Captain James Cook to Tahiti to observe Venus' second transit in 1769.

Today most people know about James Cook as the discoverer of New Zealand and the east coast of Australia but are not aware of the public reason for his voyage. The instructions from the Admiralty concerning investigations of the postulated continent of the south were in fact given in a sealed envelope, not to be opened before departure from port, so that the official motivation for Cook's voyage would be known to the competing imperial powers as the observation of the transit of Venus.

The cost of Cook's voyage for the British state budget was comparable in relative terms to the cost incurred bu the USA to send a man to the moon. May the other powers marvel at Britain's generosity to support a scientific endevour of benefit to all; the real value of the financial outlay becomes clear to those who could access the secret orders.