What type of orbits did Kepler describe?

Kepler described planetary orbits as elliptical, meaning that they are shaped like elongated circles. This was a groundbreaking revelation because, prior to Kepler, the dominant belief was that planets moved in perfect circular orbits. His first law of planetary motion states that each planet moves in an ellipse with the Sun at one focal point. This means that the distance between the planet and the Sun varies as the planet travels along its orbit, which accounts for the changes in speed that Kepler also noted. The recognition of elliptical orbits was crucial in advancing the understanding of celestial mechanics and laid important groundwork for later developments in physics and astronomy, particularly Newton's laws of motion and universal gravitation.