The transit of Venus

This won't happen again in your lifetime - get outside!

First published on 7 May 2012. Updated on 7 Jun 2012.

This event has finished

Is the morning star a star or a planet? How about the evening star? You got it, they are both Venus. But how often can you see Earth's sister planet not reflecting the sun's light, but actually casting a shadow across it? (Never look at the sun unprotected.) Your last chance ever to see the Transit of Venus will be on Wednesday 6 June.

At 8.16am in Sydney, eclipse-goggled sungazers will see a little dark dot start cutting a toothmark into the sun, making a U-turn about 11.30am and exiting around 2.44pm. Its next such incursions will be in 2117 and 2125. Northern Australia is perhaps the best place in the world for this transit, due to time zone and clear skies, but even down south we have a long window to hope for a break in the clouds. Check your protective eyewear for standards rating and cracks; it's safer to make a pinhole camera or watch it live online.

Captain James Cook had excellent conditions in Tahiti where he was sent to observe the 1769 transit. He reached Botany Bay a year later. Cook was stressing about recording the exact times because this information was to be used in comparison with readings from elsewhere across the globe to estimate the distance of Earth to the sun.

From Cook's log:

"Saturday 3rd [June] This day prov'd as favourable to our purpose as we could wish, not a Clowd was to be seen the Whole day and the Air was perfectly clear, so that we had every advantage we could desire in Observing the whole of the passage of the Planet Venus over the Suns disk: we very distinctly saw an Atmosphere or dusky shade round the body of the Planet which very much disturbed the times of the contacts particularly the two internal ones. D r Solander observed as well as Mr Green and my self, and we differ'd from one another in observing the times of the Contacts much more than could be expected."