THE coming transit of Venus, where the planet Venus passes between the Sun and the Earth, will almost certainly be the last chance any of us have to see it.
Set to occur on 6th June 2012, it will not happen again until 2117.
Acting Government Astronomer Ralph Martin says the transits occur every 105.5 or 121.5 years in pairs eight years apart, the last being in 2004.
The previous pair was in 1874 and 1882, and before that, in 1761 and 1769.
Scientific expeditions were sent to distant places to observe the 18th Century transits.
One of these was Captain James Cook’s Endeavour voyage, which stopped at Tahiti to observe the 1769 transit before following secret orders to sail west and “discover the Great South Land” we now know as Australia.
University of Western Australia physicist Dr Ron Burman says transit of Venus observations were particularly important to science in previous decades because they provided an opportunity to calculate the distance from the Sun to the Earth, using triangulation.
“By that stage astronomers could measure the relative distances within the solar system,” he says.
“They could tell reasonably accurately how far Venus was from the Sun in terms of Astronomical Units.”
An Astronomical Unit (AU) is the mean distance from the Earth to the Sun.
“They could tell the distances among the planets, and the planets from the Sun, in terms of the Astronomical Unit, but they didn’t have an accurate measure of how big the Astronomical Unit is in terms of miles,” Dr Burman says.
“The idea … was to observe the transit from two widely separated points on the surface of the earth so you get a different angle on it — basically a surveying job.”
Mr Martin cautioned people against looking directly at the sun as it can damage the retina and cause permanent loss of eyesight.
Although so-called ‘eclipse glasses’ are available they are easily damaged and become unsafe.
He said the safest way to observe the transit is on the internet.
“You can also make a pinhole projector, you get a sheet of cardboard and punch a hole in it and use a second piece of cardboard as a screen — you can project an image of it. You can also use binoculars or a telescope as a projector.”
“You can also use grade 14 welders’ glasses.”
The transit will be visible from Perth all morning on 6th June.