Venus Transit Images Reveal Parallax Effects and Measure of Distance to Sun

Six hours of observational video and 5000 individual images of the transit of Venus June 6, 2012, taken by optical and solar telescopes from two different locations on Earth and they clearly show the parallax effects that have made Venus transits so important historically.

Parallax means that when the transit is viewed from widely separated points on Earth's surface, Venus appears to follow a different path in front of the Sun's disc. 

The smooth Venus motions were at times hampered by the cloudy conditions creating gaps in the data. The observations were taken from Svalbard in Norway and Canberra in Australia, about 11600 km apart.

The parallax effect becomes very obvious when the images from the two locations are superimposed. Precise observations of the duration of the transit, together with an accurate measurement of the distance between the observation points means that the distance to Venus and to the Sun can be calculated via triangulation.

The results were presented at the European Planetary Science Congress in Madrid, Spain. Two of the observers, Miguel Perez Ayucar and Michel Breitfellner are on the science operations planning team for the Venus Express satellite, which has been orbiting Venus since 2006.

"During the hours of the transit we were delighted by the slow, delicate, gracious passage of Venus in front of the Sun. 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," Perez Ayucar said.

"In the 18th century people realised that transits of Venus could be used to measure the distance from 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," said Breitfellner.

Colin Wilson, Operations Scientist for Venus Express, 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!"