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The past importance of transits of Venus

1 Jun 2012, 00:52 UTC
The past importance of transits of Venus
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A French cartoon showing a view of the 1761 transit of Venus. Note the devil in the background, which I assume is meant to remind the reader that viewing the transit through a telescope without proper eye protection is a deadly sin (at least for your retina) Image Credit: NASA Goddard Space Flight Center Sun-Earth Day

Next week's transit of the planet Venus across the sun gives us the chance to learn a little history of transits and their scientific importance. In a couple days, I'll discuss the current scientific interest of transits.

The importance of Venus transits starts with the famed astronomer Johannes Kepler, who, in the early 1600s, was the first person to figure out the shape and properties of planetary orbits. His three laws of planetary motion allowed Kepler to figure out the relative size of the solar system. If we call the average distance between the Earth and the Sun as 1 Astronomical Unit, then Kepler knew the distances to other planets in terms of this unit. For example, he knew that Venus was about 0.7 Astronomical Units. The problem was, Kepler didn't know what an astronomical unit was in terms of familiar units like ...

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