Leon Watson, age 13, of Freeport, I11., for his question:
WHO WAS JOHANNES KEPLER?
Johannes Kepler was one of the world's great early scientists. He was a German astronomer and mathematician who discovered the three laws of planetary motion.
Kepler's three laws later formed an indispensable part of Sir Isaac Newton's discovery of universal gravitation. Here are those three laws:
1. Every planet follows an oval shaped path, or orbit, around the sun, called an ellipse. The sun is located at one focus of the elliptical orbit.
2. An imaginary line from the center of the sun to the center of a planet sweeps out the same area in a given time. This means that planets move faster when they are closer to the sun.
3. The time taken by a planet to make one complete trip around the sun is its period. The squares of the periods of two planets are proportional to the cubes of their mean distances from the sun.
Kepler was born in Wail, Germany, in 1571 and was graduated from the University of Tubingen. He accepted an offer to teach at the University of Graz but left rather than undergo compulsory conversion to Roman Catholicism.
When he was looking for another teaching position, Kepler formed an association with Tycho Brahe, which shaped the rest of his life. Brahe, the greatest astronomical observer before the introduction of the telescope, needed an assistant, the Kepler joined him.
After Brahe died, Rudolph II, the Holy Roman Emperor, appointed Kepler to be Brahe's successor as imperial mathematician.
Kepler made his most significant discoveries when he tried to find an orbit to fit all Brahe's observations of the planet Mars. He realized that the orbit couldn't be circular. The ellipse worked and Kepler destroyed a belief 2,000 years old.
Earlier astronomers thought a planet's orbit was a circle or a combination of circles. But Kepler could not find a circular arrangement to agree with Brahe's observations. And then his ellipse theory worked.
Kepler was the first astronomer to uphold openly Copernicus' theories. He also suggested a better combination of lenses for telescopes.
Kepler died in 1630.
Tycho Brahe was a Danish astronomer. He lived from 1546 until 1601.
The first new star to be noticed in 1,600 years was observed by Brahe in 1572. The discovery disproved the ancient idea that no change could occur in the heavens.
Brahe demolished another ancient idea when he showed that the comet of 1577 did not originate in the earth's atmosphere, but was a body moving through outer space.