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Venus transit 2012: a chance to test Earth-hunting techniques (+video)

Venus's 2012 transit across the sun will let researchers test methods for observing Earth-like planets light years away. It's an opportunity that won't be available again until December 2117.

NASA's planetary scientist Lori Glaze discusses the transit of Venus.
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There's a little black spot on the sun today.
No you don't want to miss this rare display. (With apologies to Sting)

It's V-Day 2012, the day Venus transits the sun, appearing as a black dot against the star's searing surface. It's a show that won't make its celestial revival until December 2117.

For many skywatchers, this event is drawing eyes because it is rare and intimately tied to the history of humanity's quest to take the measure of its corner of the cosmos. In the 18th and 19th centuries, scientists risked their lives traveling to far-flung corners of the globe to carefully record the track of the first lady of the solar system across the sun. Back then, it was the best means available for trying to estimate the Earth's distance from the sun and derive a size for the solar system.

But for some astronomers, Tuesday's transit offers an unique opportunity to use Venus as a surrogate for Venus- and Earth-size planets orbiting other stars, as researchers hone their skills at analyzing potential havens for life outside the solar system.

For others, the transit could help unravel a longstanding mystery about Venus itself: What drives the "super rotation" of its atmosphere? Venus spins on its axis once every 243 days. Its atmosphere performs the same feat in four days, with winds traveling at nearly 450 miles an hour.

A long time to wait

Venus's transits owe their century-scale frequency to the orbital paths Earth and Venus trace around the sun.

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