My husband found me this spectacular shot of the transit. I forgot to mention in my prior post why people went to such trouble to view the transit every century or so from as many spots on the globe as they could manage. (Captain Cook, for instance, arranged to watch it from the South Pacific.) The purpose was to use the parallax effect to estimate the distance of Venus from the Sun. Astronomers already had a pretty good idea of the relative size of various planetary orbits, but hadn't figured out a way to put an absolute measurement on any of them. Accurate measurements of the timing of the Venus transit from distant spots on Earth permitted a triangulation that yielded not only the distance of Venus from the Sun but also, by extension, the distance of the other planets.
By Texan99 on Friday, June 08, 2012