Johannes Kepler, working with data painstakingly collected by Tycho Brahe without the aid of a telescope, developed three laws which described the motion of the planets across the sky. . in this law both a radical departure from the astronomical prejudices of the time and profound tools for predicting planetary motion with great accuracy. Kepler, however, was not able to describe in a significant way why the laws worked.
Kepler's three laws of planetary motion can be described as follows:
The Law of Ellipses:
The path of the planets about the sun is elliptical in shape, with the center of the sun being located at one focus.
The Law of Equal Areas
An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time.
The Law of Harmonies
The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun.