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What the transit of Venus tells us about alien planets (+video)

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Planetary transits through history

Historically, planetary transits have offered a rare chance for scientists to learn about the solar system.

In the 18th century, transits of Venus provided astronomers with the first way to measure the absolute size of the solar system, including the distance from the Earth to the sun, which wasn't known at the time. Astronomer Edmond Halley first came up with the method of comparing measurements made from various locations on Earth to triangulate the distances to Venus and the sun.

This technique was successfully put into practice during expeditions to observe the Venus transits of 1761 and 1769 from around the world.

And even as recently as 2006, the transit of Mercury was used to measure the size of the sun. A group of astronomers from Hawaii, Brazil and California used NASA's Solar and Heliospheric Observatory (SOHO) to time the transits of Mercury across sun in 2003 and 2006, enabling the most precise measurement yet of the diameter of the sun.

"Transits of Mercury occur 12 to 13 times per century, so observations like this allow us to refine our understanding of the sun’s inner structure, and the connections between the sun’s output and Earth’s climate," one of the members of the team, University of Hawaii astronomer Jeff Kuhn, said in a statement.

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