Astronomer Marek Kukula from the Royal Observatory at Greenwich explores the scientific implications of the forthcoming transit of Venus across the face of the Sun, a rare astronomical event that will not occur again until 2117. Previous transits have helped establish fundamental facts about our solar system, including the distance and relative positions of all the planets that orbit our sun. But now, the forthcoming transit in June 2012, the last this century, will help planet hunters searching for other worlds across the galaxy (exo-planets). As Marek discovers, technology now makes it possible to pinpoint not only a planet's mass, size, and distance from its star but we can also establish whether it has an atmosphere and what that atmosphere might consist of and therefore whether it could theoretically support life. Thanks to the next transit event, the search for another Earth has taken a bold step forward.(Image: Venus (black dot) is silhouetted as it orbits between the Sun and the Earth during the transit of Venus seen from Bangkok on 6 June 6 2012. Credit: AFP/Getty Images)

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