Johannes Kepler (1571-1630)
Johannes Kepler who was one of the founders of modern astronomy was born on December27, 1571, at Weil, now in southwestern Germany. He had an attack of small pox when he was three which left him with crippled hands and poor eyesight. However, in spite of these handicaps he attended the University of Tubingen and proved himself a brilliant scholar. It was at Tubingen that he learned of the astronomical discoveries of Copernicus.

In 1594, Kepler was made professor of mathematics at the University of Graz, Austria. Much of his work was connected with astronomy. There he became a friend of Tycho Brahe a Danis astronomer. However, only after four years at Graz, Kepler was dismissed from his post because his Protestant beliefs were unpopular in a Roman Catholic country.

Tycho who was then working as Imperial Mathematician to the Emperor Rudolph II, invited Kepler to be his assistant at his observatory near Prague, which is now the capital of Chechoslovakia. In 1601 Tycho died and Kepler took his place as Imperial Mathematician.

Using Tycho`s astronomical observations Kepler discovered three very important facts about the way in which the planets move. These facts are often known as "Kepler`s Laws." The first law states that the planets move around the sun in slightly oval path called `ellipses`, and not in circles. The second law tells how quickly a planet moves at any point of its ellipse. The third law tells us how long a planet takes to travel around an ellipse of any particular size.

The knowledge of these three laws helped Sir Issac Newton to discover the three laws of gravitation.