Johannes Kepler has empirically set up his three laws, consequence of the universal gravitation highlighted per Newton, which establish the rules of the elliptic movement of two bodies only submitted to their reciprocical attraction. The three laws are the followings: 1- The planets describe elliptical orbits whom the Sun is one center. 2- Law of the areas: During the movement, the radius vector planet-sun covers areas during equal times. 3- The ratio of the [cube of the semi-long axe of the orbit] per the [square of the period] has the same value for all the planets. See orbit, gravity