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Kepler’s Laws of Planetary Motion

Kepler after a life time study worked out three empirical laws which govern the motion of these planets and are known as Kepler’s laws of planetary motion. These are
Law of orbits Every planet moves around the Sun in an elliptical orbit with Sun at one of the foci.
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 (Fig. 13). According to this law, the planet will move slowly when it is farthest from Sun and more rapidly when it is nearest to sun. It is similar to the law of conservation of angular momentum.
Fig. 13

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.
T 2 ∝ a3

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