Handout image courtesy of NASA shows the planet Venus at the start of its transit of the Sun, June 5, 2012. One of the rarest astronomical events occurs on Tuesday and Wednesday when Venus passes directly between the sun and Earth, a transit that won't occur again until 2117. [Photo/Agencies]

The planet Venus starts its transit across the sun as seen from Newcastle, Australia June 6, 2012. [Photo/Agencies]