What the transit of Venus tells us about alien planets (+video)
The transit of Venus will help astronomers on the hunt for planets outside of our solar system.
A rare opportunity to see the planet Venus cross in front of the face of the sun is coming up next week.
On June 5 to 6, Venus will "transit" the sun for the last time until 2117, joining the ranks of the handful of planetary transits that have occurred since the dawn of modern astronomy.
From our vantage point on Earth, we occasionally have the chance to see two planets — Venus and Mercury — pass in front of the sun, as these are the only two planetary bodies between us and our star.
Transits of Mercury are more common than Venus transits, with an average of 13 occurring each century. Venus transits come in pairs separated by eight years, with more than a century usually elapsing between one pair and the next. [Gallery: Transits of Venus Throughout History]
"The first transit ever observed was of the planet Mercury in 1631 by the French astronomer [Pierre] Gassendi," Fred Espenak, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md., wrote on the NASA Eclipse website. "A transit of Venus occurred just one month later, but Gassendi's attempt to observe it failed because the transit was not visible from Europe. In 1639, Jeremiah Horrocks and William Crabtree became the first to witness a transit of Venus."
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