(1) The law of Orbits : Every planet moves around the sun in an elliptical orbit with sun at one of the foci.
(2) The law of Area : The line joining the sun to the planet sweeps out equal areas in equal interval of time. i.e., areal velocity is constant. According to this law planet will move slowly when it is farthest from sun and more rapidly when it is nearest to sun. It is similar to law of conservation of angular momentum.
Areal velocity dA/dt = L/2m
(3) The law of periods : The square of period of revolution (T) of any planet around sun is directly proportional to the cube of the semi-major axis of the orbit.
where a = semi-major axis
r1 = Shortest distance of planet from sun (perigee).
r2 = Largest distance of planet from sun (apogee).
• Kepler’s laws are valid for satellites also.
