Johannes Kepler (1571-1630) was a German astronomer noted for his three laws of planetary motion. These laws are now known as Kepler's laws.

Kepler was influenced by a mathematics professor, Michael Maestlin, who was an early believer in the heliocentric theory (sun-centered universe) developed by the Polish astronomer Nicolaus Copernicus. In 1594, came up with measurements for the orbits of the planets, which he wrongly assumed were circular. Kepler later figured out that planetary orbits are elliptic (moving in the space of a flattened out circle. Still his original measurements were within 5% of the actual measurements. Kepler’s ideas were used to help convince other astronomers that Copernicus’ theory was correct.

Kepler became an assistant to the Danish astronomer Tycho Brahe. When Brahe died Kepler assumed his position as mathematician and court astronomer to Rudolf II, the Holy Roman emperor. He then came up with his laws of planetary motion—the planets move in elliptic orbits around the sun and the closer a planet comes to the sun, the quicker it moves.

At about the same time he began publishing a book, the Epitome Astronomiae Copernicanae (Epitome of Copernican Astronomy, 1618-1621), which became the first textbook of astronomy to be based on Copernicus’ theory.

The English scientist Sir Isaac Newton used Kepler's theories and observations to come up with his theory of gravity in 1687.

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