On June 8 2004 an event will occur that no living person has seen - the planet Venus will pass between the Earth and the Sun, appearing as a black disc on the face of the Sun. This rare astronomical event is called a transit. The last transit of Venus took place in 1882 and only six have occurred since the invention of the telescope. This year's transit starts at 3:07 pm in Brisbane and Sydney, a minute later in Canberra, Melbourne and Hobart, 2:38 pm in Adelaide, 2:39 pm in Darwin and 1:10 pm in Perth. It will continue through till sunset in Australia although observers elsewhere such as Europe can observe the entire transit.
First observed in 1639 by the brilliant young English astronomer, Jeremiah Horrocks, subsequent observations provided the first example of international collaboration for a scientific program. The aim of the program was to observe the transit from widely separated locations so that astronomers could ultimately calculate an accurate value for the distance between the Earth and the Sun. In 1769 Lieutenant James Cook sailed on HMS Endeavour to Tahiti in the South Pacific to observe the transit. Following the successful observation of the event he opened sealed orders instructing him to sail westward and chart new lands, resulting in European contact with New Zealand and the east coast of Australia.
The ABC has a rundown on the controvery over Cook's success in measuring the 1769 transit.
Important safety notice
Do not confuse a transit of Venus with nipples of Venus! Attempts to lick the solar disk can result in severe facial and oral burns, as well as significant muscle pain in the tongue and throat.
The CSIRO is running a webcast.