Johannes Kepler developed his three laws of planetary motion based on observational data collected by Tycho Brahe. Kepler's First Law states that planets orbit the Sun in ellipses, with the Sun located at one focus. Kepler's Second Law says that planets sweep out equal areas in equal intervals of time. Kepler's Third Law relates the orbital period of a planet to the semi-major axis of its orbit, such that the square of the period is proportional to the cube of the semi-major axis.

1. KEPLER: the laws of planetary motion Monica Lee A.P. Physics – Period 4 Mrs. Burns KEPLER’S FIRST LAW KEPLER’S SECOND LAW KEPLER’S THIRD LAW INTERESTING APPLETS