AstronomyCast Johannes Kepler's Laws of Planetary Motion

Johannes Kepler was born one month premature, and in 1571 that was much more serious than it is now. Because of his early birth, physical ailments plagued him for most of his life. It is believed that because of this his eyesight was poor, which was why he did not make many of the observations he used himself. Instead he worked with Tycho Brahe until the two had a falling out. Once Brahe died, Kepler managed to get his hands on some of Brahe's great observations and data logs. With the data from Brahe and through the use of mathematics Kepler was able to make three laws of planetary motion.

• 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 Ellipses)
• 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 Equal Areas)
• 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. (The Law of Harmonies)