Johann Kepler (1571 – 1630) was a German astronomer and mathematician to whom scientists owe a great debt. It was he explained the way in which the planets move in our solar system. Earlier, Copernicus had shown that the planets travel around the Sun (and not, as thought, round the Earth) Galileo was able to confirm this by observation through his telescope.

Another important name in early astronomy was Tycho Brahe (1546 – 1601) who, although he did not accept Copernicus’s theories, spent much of his life in developing accurate measuring instruments and in compiling astronomical tables on the movements of the planets.

In 1600 Johannes Kepler was appointed Brahe’s assistant at an observatory in Prague. When Brahe died the following year, Johannes Kepler continued his work on the tables. When these were completed he had more information on the behavior of the planets than anyone had possessed before. With this knowledge, he was able to interpret their movements and to produce three basic laws by which they moved.

Johannes Kepler noted first that planets move round the Sun in an oval or elliptical path. Secondly he said that a line between a planet and the Sun swept out equal areas in equal times. In other words the nearer a planet is to the Sun, the faster it travels. His third law demonstrated that planets nearer the Sun have a shorter year than those further away from it.

These were by no means the only contribution made to astronomy by Johannes Kepler. He studied, for example, the passage of comets and the star explosions called novae. But his real achievement lay in his laws, which lad open the way for the great discoveries of Isaac Newton about gravity and motion.

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