Saturday, May 26, 2012

Countdown to Transit of Venus

A curious composite image from the TRACE solar observation satellite, watching the planet Mercury move across the sun in 2003.

Parallax shift as recorded by TRACE satellite (orbiting Earth)
 recording the Transit of Mercury 2003.
Image source  
No - Mercury isn't wobbling ... it's the satellite taking the photos that is moving, orbiting Earth on a North-South path. Mercury thus appears to move up or down, depending whether the satellite is North or South of the equator when the image is taken.  While man-made satellites able to photograph Mercury passing the sun are relatively new, people have been measuring the parallax shift during the transit of Venus since 1761 by sending observers to different points across the globe. Australians feel a particular affinity with the Transit of Venus: measuring it was a key motivation for Cook's voyage on the Endeavour.  In two weeks, Venus does it again - the last chance to see it in your lifetime. Australian students and their teachers are particularly fortunate as the ToV event starts and ends with the school day on June 6th.

Looking for activities to do with students? has an impressive one-stop collection of resource links. With so many to choose from, here's a short list we are using in our mathematics faculty to prepare students for watching the event:
  • Two videos we found to be high both engaging and high quality, with mathematical content suitable for all ages:

If you like the idea of using satellite imagery to demonstrate the parallax shift, it's interesting to compare image from TRACE (which does orbit the Earth), to that taken by SOHO (which does not orbit the Earth):

No parallax shift from SOHO images!
Transit of Mercury 2003. Photo: NASA.

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