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Johannes Kepler was a famous German scientist who figured out how planets and satellites orbit larger objects. He was born on December 27, 1571 in Leonberg, Germany. His father was a soldier and his mother was an innkeeper’s daughter. His family thought Kepler should become a minister because he was in poor health as a child.

He attended a local school and a seminary until he entered the University of Tubingen. At the university, he studied mathematics, astronomy, Greek, and Hebrew. He was very good at his studies and was chosen to learn about Copernicus’ theories of the solar system. Kepler believed the Copernican system was correct. He was so outstanding at his studies that he decided not to become a minister. Instead he became a mathematics professor in Graz, Austria from 1593 - 1598. In 1596, he developed a model of the planets from Mercury to Saturn. His findings were published in a book entitled Mystery of the Cosmos. A copy of this work was sent to Tycho Brahe, an important astronomer. Brahe was so impressed with Kepler’s work that he hired Kepler as his mathematical assistant.

When Brahe died in 1601, Kepler took Brahe’s place as Imperial Mathematician under Holy Roman Emperor, Rudolph II. Although this was an good position, Kepler earned little money and was very poor. Kepler used Brahe’s measurements concerning Mars’ position in the sky to determine the planet’s orbit. In 1609 and 1619, he published works that were later called Kepler’s Laws.   These laws explained the planets' elliptical orbits, orbital speed, and orbital relationships to other planets.

Kepler and Galileo exchanged letters. Galileo sent Kepler a telescope. With this telescope, Kepler saw Jupiter’s moons. He called them satellites. This was the first time the word "satellite" referred to an orbiting body.

In 1611, Kepler discovered a better telescope design. His design used convex lenses instead of the one convex and concave used by Galileo.

Kepler was raised his entire life as a Lutheran. In 1612, he was excommunicated. The Lutheran church felt his ideas were too radical.

On November 15, 1630, Kepler died in Regensburg. He was an important person in science’s attempts to learn more about the solar system.

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