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ScienceCasts The 2012 Transit of Venus
music The 2012 Transit of Venus presented by Science@NASA One little black spot on the sun sure can cause a lot of fuss. Twice every 120 years, Venus passes directly in front of the sun. The circular spot the planet makes on the solar disk is not much bigger than an ordinary sunspot, but every time it happens,
it is a worldwide sensation. The next Transit of Venus is on June 5th, 2012, and for the first time since the 19th century the event will be visible across all of North America. The nearly 7hour transit begins at 3:09 pm Pacific Daylight Time. Observers on seven continents, even a sliver of Antarctica,
will be able to see it. Across the United States, the transit is at its best around sunset a rare photoop for creative photographers. Observing tip: Do not stare at the sun. Venus covers too little of the solar disk to block the blinding glare. Instead, use some type of projection technique
or a solar filter. A 14 welder's glass is a good choice. For some observers, the view provides an unsettling sense of scale. Venus seems so small and fragile against the solar disk; our own planet is equally miniscule. Others say it looks like a black hole punched in the surface of the sun very strange.
Transits of Venus first gained worldwide attention in the 18th century when one of the biggest mysteries of science was the size of the solar system. It might seem amazing today, but astronomers didn't know the absolute distance between any two planets. How many miles would you have to travel to reach another worldé The answer was as mysterious then as the nature of dark energy is now.
Venus was the key, according to astronomer Sir Edmund Halley. He realized that by observing transits from widelyspaced locations on Earth it should be possible to triangulate the distance to Venus. The idea galvanized scientists who set off on expeditions around the world to view a pair of transits in the 1760s. The great explorer James Cook himself