Kepler laws of planetary motion

 

Kepler, on the basis of the data on the motion of planet Mars collected by his chief , Tycho Brahe,at the Royal observatory at Prague,succeeded after 22 years of ceaseless work in evolving the famous three laws known after him - the first two in the year 1609 and the third ,ten years later, in 1619. These laws have an historical importance in that they provided the original experimental evidence on the validity of Newton's laws of mechanics as also his theory of gravitational attraction.  The three laws may be stated as

1st law:

The path of a planet is an elliptical orbit around tge sun with the sun at one of its foci. This is aptly known as the law of elliptical orbits and obviously gives the shape of the orbit of a planet around the sun .

2nd law:

The radius vector ,drawn from the sun to a planet ,sweeps out equal area in equal interval of time .ie,areal velocity is constant. This referred to the law of areas and gives the relationship between the orbital speed of planet and its distance from the sun.

3rd law:

The square of a planet year,ie.,its time-period(or its time of one complete round of the sun) is proportional to the cube of the semi-major axis of its orbit. This is known as the harmonic law and gives the relationship between the orbital speed of the planet and its distance from the sun.