Kepler's Laws

Kepler's laws are three empirical laws of orbital motion formulated by Johannes Kepler in the early 17^th century, based on observations of planetary motion made by Tycho Brahe. Although originally derived for planets orbiting the Sun, the laws apply equally to the motion of natural and artificial satellites orbiting the Earth.

First law: A satellite moves in an elliptical orbit with the Earth located at one focus of the ellipse; the satellite’s orbital velocity is therefore not uniform.

Second law: The line joining the satellite and the center of the Earth sweeps out equal areas in equal times, implying that the satellite moves faster near perigee and slower near apogee.

Third law: The square of the orbital period of a satellite is proportional to the cube of the semi-major axis of its orbit.