Johannes Kepler, in his study of planetary motion, noticed that the planets do not move in perfect circles, as had been traditionally believed. Instead, he observed that the orbits of the planets are elliptical in shape. This observation led him to formulate his First Law of Planetary Motion, known as Kepler's First Law, which states:
"The orbit of a planet around the Sun is an ellipse, with the Sun at one of the two foci."
This was a significant departure from the circular orbits suggested by earlier astronomers, such as Claudius Ptolemy and even Copernicus, who proposed circular orbits for the planets in his heliocentric model. Kepler's discovery of elliptical orbits laid the groundwork for the later development of celestial mechanics and improved the understanding of planetary motion in the solar system.
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