* Early observations: Astronomers before Kepler, like Tycho Brahe, had made incredibly precise observations of planetary motions, especially Mars. These observations provided crucial data for Kepler's work.
* Kepler's Laws: Kepler used Tycho's data to formulate his three laws of planetary motion. The first law states that planets move in elliptical orbits with the Sun at one focus.
* Prior Theories: Before Kepler, the prevailing theory was that planets moved in perfect circles, as proposed by Ptolemy's geocentric model.
Therefore, Kepler didn't just "discover" elliptical orbits; he proved that planets follow elliptical paths, challenging the established circular model. This discovery was a major breakthrough in astronomy and marked a significant step towards our understanding of the solar system.
