Johannes Kepler (left, 1571-1630), German astronomer, and Tycho Brahe (right, 1546-1601), Danish astronomer, discussing planetary observations. Brahe

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Johannes Kepler (left, 1571-1630), German astronomer, and Tycho Brahe (right, 1546-1601), Danish astronomer, discussing planetary observations. Brahe made naked eye observations, as telescopes had not yet been invented. In 1599, he established an observatory at Benatky Castle near Prague (now in the Czech Republic), under the patronage of the Holy Roman Emperor. From 1600, after reading Kepler's Mysterium Cosmographium (1596), Brahe employed Kepler to help make observations of the planet Mars. Kepler made use of these observations when devising his three laws of planetary motion, in which he showed that planets move in ellipses rather than circles.

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