*By Tim Lambert*

Johannes Kepler was one of the great astronomers of the 17th century. Kepler was born in Weil der Stadt in southern Germany on 27 December 1571. His father Heinrich was a mercenary soldier. Johannes family were poor but in 1588 he won a scholarship to study theology at the University of Tubingen. (Kepler was a Lutheran). At first Johannes planned to become a theologian but while at university he became interested in astronomy. (However Kepler remained a devout Christian for the rest of his life). While he was at university Kepler met a man named Michael Maestlin, who believed in the Copernican theory of the universe. (In the early 16th century people believed the Sun, Moon and the other planets orbited the Sun. Copernicus challenged this theory in a book published in 1543. He claimed that the Earth and the other planets orbit the Sun. Kepler became convinced the Copernican theory was correct and he set out to prove it.

In 1594 Kepler became a teacher of mathematics at Graz in Austria. In 1596 he published his book The Cosmic Mystery which defended the Copernican system. In 1597 Kepler married his first wife, Barbara.

In 1600 Kepler was forced to leave Graz because of the Catholic Counter-Reformation. Kepler moved to Prague. In 1601 he was appointed Imperial Mathematician to the Holy Roman Emperor (who ruled most of central Europe). In 1604 Kepler published his great work The Optical Part of Astronomy in which he studied how lenses work and also how the human eye works. Then in 1604 a new star appeared (today we call it a supernova). In 1606 Kepler described the phenomena in his book On the New Star.

In 1605 while he was trying to calculate the orbit of Mars Kepler realized it moved in an ellipse. Until that time astronomers believed that planets orbited in circles. Kepler realized the orbits of planets are elliptical. He also realized that a planet moves faster when it is closer to the Sun and slower when it is further away from the Sun.He published his observations in a book called New Astronomy in 1609.

In 1611 Kepler's wife Barbara died. His son Friedrich also died. Then in 1612 Kepler was forced to leave Prague and he moved to Linz. He married his second wife, Susanna in 1613. Johannes Kepler published his work Harmony of the Worlds in 1619.

Meanwhile in 1613 Kepler calculated that Jesus was born in 4 BC.

Between 1618 and 1621 Kepler published his last great work, Epitome of Copernican Astronomy. It was published in 3 volumes.

Kepler also wrote a story about a trip to the Moon called The Dream, which was published after his death, in 1634. It could be called the first science fiction story.

Johannes Kepler died of fever on 15 November 1630. He was buried in Regensburg.

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