What did Johannes Kepler discover regarding planetary motion?

Johannes Kepler is renowned for his formulation of the laws of planetary motion, which fundamentally transformed our understanding of the solar system. His most significant discovery was that planets move in elliptical orbits rather than circular paths. This was a groundbreaking realization because it contradicted centuries of belief in perfect circular orbits, which stemmed from Aristotelian and Ptolemaic models.

Kepler's first law, often called the law of ellipses, explicitly states that each planet's orbit is shaped like an ellipse—a geometric figure that has two focal points. In the case of our solar system, one of those focal points is the Sun. This insight helped to explain variations in planetary speeds and distances from the Sun, which could not be accurately accounted for under the circular orbit model.

By recognizing that orbits are elliptical, Kepler provided a more precise framework for understanding the motions of celestial bodies, laying the foundation for Newton's later work on gravitation. This was pivotal in shifting the scientific perspective from geocentrism to heliocentrism, greatly influencing the field of astronomy.