Scientists and amateur astronomers around the world are preparing to observe the rare occurrence of Venus crossing the face of the sun on 5-6 June, an event that will not be seen again for more than 100 years.
A transit of Venus occurs only when Venus passes directly between the sun and Earth. Since the orbital plane of Venus is not exactly aligned with that of Earth, transits occur very rarely, in pairs eight years apart but separated by more than a century.
The last transit was in June 2004 but the next will not be seen until 2117.
The Venus transit next month will be visible in its entirety (about six hours) only from the western Pacific, eastern Asia, eastern Australia and high northern latitudes. For the United States, the transit will begin in the afternoon of 5 June. For much of Europe, the sun will rise on 6 June with the transit almost finished.
If you are observing the event, never look at the sun with unprotected eyes, through ordinary sunglasses, or through a telescope, as this may cause permanent blindness. Protect your eyes at all times with proper solar filters. No matter what technique you use, do not stare continuously at the sun. Take breaks and give your eyes a rest!
See Safe Solar Viewing and Six ways to see the transit.
Venus transits are of great historical significance because they gave astronomers a way to measure the size of the Solar System.
The transits of the 18th century enabled astronomers to calculate the distance to the sun by timing how long it took for Venus to cross the solar disc from different locations on Earth and then using simple trigonometry.
During the transit of 1761, astronomers also noticed a halo of light around the planet's dark edge, revealing Venus to have an atmosphere.
NASA, the European Space Agency (ESA), and other organizations are teaming up to provide viewing tips, live webcasts, and other information.
The event in June will be the first transit while the ESA's Venus Express spacecraft is orbiting the planet. ESA will be reporting live from the Arctic island of Spitsbergen, where the Venus Express science team will discuss the latest scientific results from the mission while enjoying a unique view of the 2012 transit under the 'midnight Sun.'
NASA will also be providing a webcast from atop Mauna Kea, Hawaii on 5 June.
Venus transit resources and sources used to compile this report: