1. INTRODUCTION

 

According to the Copernican heliocentric model, these planets, including the Earth, revolve around the sun in circular orbits. However, based on Tycho Brahe’s observations, Kepler concluded that the speculated circular orbits were not in agreement with those observations. After twenty years of hard work, Kepler tried elliptical orbits, and to his amazement he observed an astonishing match. Kepler’s conclusion from this monumental work, are consummated in his three well-known laws of planetary motion.  [2]

 

 

1. The orbit of a planet is an ellipse with the sun at one of its foci. 2. The line joining the sun to a planet sweeps over equal areas in equal intervals of time, regardless of the length of the line. 3. The square of the period of any planet is proportional to the cube of its mean distance from the sun. Aristarchus idea, restored by Copernicus, and advanced by Kepler, culminated to its full development by the genius of Isaac Newton. With Kepler’s empirical discoveries at hand, Newton endeavoured to answer two fundamental questions.

 

(1).What force causes the planets to revolve around the sun.

(2).Why their orbits are elliptical. In his pursuit to find answers to these two questions, Newton discovered the theory of ”UNIVERSAL GRAVITATION”.