Astronomers catch Venus transit on film
Researchers from the European Space Astronomy Centre (ESAC) in Spain succeeded in putting the transit of Venus on film after observing it from two locations (Svalbard, Norway and Canberra, Australia) on Earth on 6 June 2012. The films point out the parallax effects that made Venus transits historically significant. The results were presented at the recent European Planetary Science Congress (EPSC) in Madrid, Spain, organised by Europlanet, a Research Infrastructure linking laboratories and funded under the EU’s Seventh Framework Programme (FP7).
ESAC researchers Miguel Pérez Ayúcar and Michel Breitfellner compressed 6 hours of observations and 5,000 single images into two movies. They used optical and solar telescopes to generate the films into a 40-second video. Despite data gaps triggered by cloudy conditions, the motion of the planet across the Sun disk is smooth. Both astronomers are members of the science operations planning team for the Venus Express satellite, which has been orbiting Venus for the last six years.
They said by superimposing the images from both locations they produced the parallax effect. Parallax means that when the transit is observed from widely separated points on the surface of the Earth, Venus seems to follow a different path in front of the Sun’s disc.
Triangulation is a possible method to calculate the distance to Venus and to the Sun when precise observations of the transit’s duration are made, along with an accurate measurement of the distance between the points of observation.
‘During the hours of the transit we were delighted by the slow, delicate, gracious passage of Venus in front of the Sun,’ said Mr Pérez Ayúcar. ‘A perfect black circle, containing a world in it, moving in front of its looming parent star. How thankful we were to witness it. Now with these movies, we can share a sense of that experience.’
For his part, Mr Breitfellner said: ‘In the 18th century people realised that transits of Venus could be used to measure the distance from the Earth to the Sun. Teams of astronomers were sent all across the world to measure this effect. The 2012 transit has its own historical importance – it is the first that has occurred when a spacecraft is in orbit at Venus. Science teams are now working to compare observations of the Venus transit from Earth with simultaneous observations from Venus Express.’
Commenting on the results, Venus Express operations scientist Colin Wilson said: ‘Planetary transits are not just of historical interest, they have acquired a new importance in the study of newly discovered planets around other stars. Because we cannot image exoplanets directly, it is only by studying their transits that we can discover whether they harbour liquid water or other potential ‘biomarker’ molecules like methane or ozone. The Venus transit is an example much closer to home, offering us a chance to test our understanding of how to interpret transit data. This certainly added extra interest as we watched the Venus transit in June – particularly knowing it was our last chance that we’d have to wait until 2117 to see the next one!’
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