Kepler's Laws of Planetary Motion

Johannes Kepler

In the sixteenth century, most people believed in the ideas of the ancient astronomer Ptolemy, that the planets, Moon, and Sun all orbited around the Earth. Then in 1543, Nicolaus Copernicus proposed the idea that the planets and the Earth orbited around the Sun. However, Copernicus' new theory was no better at predicting the positions of the planets in the sky than the older, Earth-centered theory. There was still something missing.....

Half a century later, Johannes Kepler sought to refine the Copernican system and truly understand how the planets move around the Sun. He studied observations of Mars recorded by his mentor, Tycho Brahe. Rather than trying to force the data to support a pre-determined view of the Universe, Kepler used Tycho's observations to guide the creation of his theories. This was a radical departure from the thought processes of his era, and it is a signal of the beginning of our modern scientific age.

In 1609, Kepler published his first and second laws of planetary motion, The Law of Ellipses and The Equal-Areas Law. Ten years later he published a third law, The Harmonic Law. He had succeeded in using a scientific method to create a simple, elegant, and accurate model to describe the motion of planets around the Sun,

The Solar System

Select a law to learn about....