Happy Venus transit day!

The weather in Melbourne has been pretty miserable for the past few days, but the Sun was shining this morning when the Venus transit commenced at around 8.15am.  A transit is an event whereby a planet passes between our line of sight and the planet’s host star — in our Solar System this means a planet passes between the Earth and the Sun.  This can only happen with Mercury and Venus.  During the transit the planet appears as a small black dot passing across the face of the Sun.

Sunset view of the 2004 transit of Venus. (Credit: Emil Lenc)

Because the orbital plane of Venus is tilted by 3.4 degrees from that of the Earth’s orbital plane, Venus transits are quite rare. They have a strange pattern, whereby a pair of transits 8 years apart is separated by 121.5 years and 105.5 years.  So since they were first discovered there have been just 6 transits of Venus: 1639, 1761, 1769, 1874, 1882 and 2004 – and now 2012. And the next one in won’t be until 2117 – so today is your last chance!

You can find out more about the history of the transit of Venus and how is can be used to determine the Earth-Sun distance (the Astronomical Unit) at this website. If you cannot view the transit in your location, you can watch a live streaming.  For more information, see:


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