Kepler's Laws of Planetary Motion

In the early 1600s, Johannes Kepler proposed three laws of planetary motion. Kepler was able to summarize the carefully collected data of his mentor - Tycho Brahe - with three statements that described the motion of planets in a sun-centered solar system.

Kepler's Three Laws

Kepler's three laws of planetary motion can be described as follows:

• Kepler’s first law of planetary motion states that the orbit of each planet is an ellipse with the Sun located at one focus. There is nothing but empty space at the other focus.

• Kepler’s second law, also called Kepler’s law of equal areas, states that the imaginary line connecting a planet to the Sun sweeps out equal areas in equal length of time.

• Kepler’s third law states that the square of the orbital period (time to complete one revolution) T of a planet is directly proportional to the cube of the mean distance r of that planet from the sun. i.e, T² ∝ r³

Did You Know?  Kepler lived in an era when there was no clear distinction between astronomy and astrology, but there was a strong division between astronomy and physics.