Hugh Pickens writes "BBC reports that astronomers are puzzled by a strange bright spot which has appeared in the clouds of Venus, first identified by US amateur astronomer Frank Melillo on 19 July and later confirmed by the European Space Agency's Venus Express spacecraft. 'I have seen bright spots before but this one is an exceptionally bright and quite intense area,' says Melillo. The bright spot has started to expand since its first appearance, being spread by winds in Venus' thick atmosphere. Scientists are unsure as to what is causing the spot. 'An eruption would have to be quite energetic to get a cloud this high,' said Dr. Sanjay Limaye of the University of Wisconsin. Furthermore, at a latitude of 50 degrees south, the spot lies outside the region of known volcanoes on Venus. Another potential source for the bright spot are charged particles from the Sun interacting with Venus' atmosphere. It's also possible that atmospheric turbulence may have caused bright material to become concentrated in one area. 'Right now, I think it's anybody's guess,' adds Limaye."