Johannes Kepler

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Nicolaus Copernicus gets most of the credit for figuring out that Earth is not the center of the universe -- that it orbits the Sun. But Copernicus left it to others to actually prove his idea right. The man who did so was born on today's date in 1571.

Johannes Kepler was one of the most gifted mathematicians of his time. He was also one of the most dedicated; he made his remarkable discoveries despite double vision in one eye and other severe health problems. He even had to defend his mother against charges of witchcraft.

Kepler served as an assistant to Tycho Brahe, who compiled catalogs of the positions of stars and planets, and succeeded Tycho as the imperial mathematician.

Kepler's great discoveries sprang from a detailed analysis of the orbit of Mars.

Like other astronomers, he assumed that Mars's orbit was a perfect circle. But through years of labor -- and 900 pages of notes and calculations -- he discovered that it's not. Instead, Kepler discovered that the orbits of Mars, Earth, and all the other planets are ellipses, so the distance between the Sun and any planet is constantly changing. Kepler also realized that planets move fastest when they're closest to the Sun, and slowest when they're at their farthest.

Beginning next year, astronomers will use Kepler's laws to calculate the orbits of planets in other star systems that are discovered with a new space telescope -- named Kepler.

Script by Damond Benningfield, Copyright 2008

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