Each century Venus passes directly between the sun and the Earth twice, eight years apart. On June 5th or 6th 2012, depending on where on Earth you are, you may be able to see the last of the 21st century’s pair of transits of Venus. The next sighting will be in 2117. Writer ANDREA WULF returns to Radio Times to discuss her tale of the 18th century’s astronomers’ first attempt to measure the size of our solar system: how far the sun is away from the Earth. Her new book, “Chasing Venus: The Race to Measure the Heavens,” describes the scientific adventurers from many countries, including Britain, France, Russia, and the American colonies, who suffered weather and international political adversities. DERRICK PITTS, chief astronomer of The Franklin Institute, will help us understand how the transit method is back in use, recently revealing extrasolar planets, thanks to developments of high-resolution telescopes.