Kepler's Laws

This eminent astronomer, born in Wurtemberg in the year 1571, determined the true laws of the motions of the planets around the sun. The three laws which he discovered, are:

First. The orbit of each planet is an ellipse having the sun in one focus.

Second. As the planet moves around the sun its radius-vector, or line joining it to the sun, passes over equal areas in equal times.

Third. The square of the time of revolution of each planet is proportional to the cube of its mean distance from the sun.