Kepler’s Laws Of Planetary Motions

Introduction Kepler’s three laws are empirical - they describe a phenomenon without explaining why it occurs. Kepler derived them from Tycho Brahe’s extensive observations.

Ellipse An ellipse is a figure that is drawn around two points called the foci. It is drawn in such a way that the distance from one focus to any point on the ellipse and back to the other focus equals a constant. The ellipse was the key to the solution of how planets move.

Kepler’s first law Using Tycho’s observations and his mathematics, Kepler was able to recognize the elliptical shape of the orbits. Kepler’s first law states that the orbits of the planets around the sun are ellipses with the sun at one focus.

Kepler’s second Law Kepler’s second law states that a line from the planet to the sun sweeps over equal areas in equal intervals of time. This means that when a planet is closer to the sun and the line connecting it to the sun is shorter, the planet moves more rapidly to sweep over the same area that is swept over when the planet is farther from the sun.