Sunday, July 13, 2003

Kepler's Laws

Till the 16th century people believed Ptolemy's ( 85 - 165 AD) words,spoken 1400 years earlier, that the planets, Moon, and Sun orbited around the Earth.

In 1543, Copernicus proposed that the planets and the Earth orbited around the Sun. But his proposal was not very useful in predicting the motion of the planets.

The world had to wait for 50 more years and Johannes Kepler to throw light on the movement of planets. Kepler had the advantage of having access to the best possible observations of his day, painstakingly collected, at an enormous expense , by his master , Tycho Brahe, a rich Danish nobleman.

These observations did not come easy to Kepler. Tycho guarded them jealously and Kepler had to wait till his master's death to get them.

Kepler writes of Tycho, "My opinion of Tycho is this: he is superlatively rich, but he knows not how to make proper use of it, as is the case with most rich people. Therefore, one must try to wrest his riches from him."

He did suceed in 'wresting Tychos' riches as he confesses ""I confess that when Tycho died, I quickly took advantage of the absence, or lack of circumspection, of the heirs, by taking the observations under my care, or perhaps usurping them..."

Armed with Tycho's precious data, Kepler was able to publish the laws of Planetary motion. In 1609, The first and second laws of planetary motion were published. Ten years later, the third law, The Harmonic Law was publisehd.

The world now had an elegent framework to study the mysterious movement of planets.

The laws below changed our understanding of heavens forever and Issac Newton's Theory of universal gravitation was made possible because of these laws.

The Law of the Ellipses :
The orbits of the planets are ellipses with the Sun at one of the foci.

The Equal Areas Law
The line that connects the planet to the Sun sweeps out equal areas in equal times.

The Harmonic law :
" The square of the orbital periods are proportional to the cube of the semimajor axes

Kepler's laws are not only valid for the Solar System, but also for any system with a massive central body with minor bodies rotating around it.


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