Kepler's laws

Kepler's laws are kinematic laws that describe the movements of celestial bodies; Newton's laws would later explain their cause (i.e. their dynamics). Though they were originally formulated to explain the movements of the planets, they can be applied to any body in orbit around another: double stars, Jupiter's moons etc. They are universal laws outside the quantum domain.

There are three laws of Kepler:

• Kepler's first law: the planets describe an ellipse in which the Sun occupies one of the foci;
• Kepler's second law: the Sun-planet radius sweeps out equal areas during equal intervals of time;
• Kepler's third law: the square of the period of revolution is proportional to the cube of the semi-major axis of the orbit.