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:
- 2012 Transit of Venus, NASA GSFC
- Safe solar viewing
- Transit of Venus, Planethunters.org
- AstroSarah’s Transit of Venus page
