Kepler's Laws Kepler's Laws Johannes Kepler, working with data painstakingly collected by Tycho Brahe without the aid of a telescope, developed three laws which described the motion of the planets across the sky. All planets move in elliptical orbits, with the sun at one focus. A line that connects a planet to the sun sweeps out equal areas in equal times. The square of the period of any planet is proportional to the cube of the semimajor axis of its orbit. Kepler's laws were derived for orbits around the sun, but they apply to satellite orbits as well.
All planets move in elliptical orbits, with the sun at one focus.
This is one of Kepler's laws . The elliptical shape of the orbit is a result of the inverse square force of gravity . The eccentricity of the ellipse is greatly exaggerated here. The eccentricity of an ellipse can be defined as the ratio of the distance between the foci to the major axis of the ellipse. The eccentricity is zero for a circle.