Who discovered planetary motion?
In the early 1600s, Johannes Kepler created three laws of planetary motion. While it was Nicolaus Copernicus who discovered that the planets revolve around the Sun, it was Kepler who correctly defined their orbits. And this gave birth to Kepler’s first law, Law of Ellipses.
What is Law of Ellipses?
While assisting a wealthy astronomer, Tycho Brahe, Kepler was asked to define orbit of Mars. For many years, he struggled to make Brahe’s observations of the motions of Mars match up with a circular orbit which was the common conclusion by many philosophers of that time.
Through Brahe’s astronomical measurements and Kepler’s own drawings of the geometrical relationship between the Sun and Mars in various parts of the planet’s orbit, Kepler eventually discovered that planets moved faster when they were closer to the Sun. From this realization, he concluded that the orbit of Mars was elliptical, not circular.