Johannes Kepler was born on 27 December 1517 in Germany. He was to grow up to be an important astronomer who made many discoveries about the stars. Astronomers study the movements of the planets, stars, comet and meteors. However, for most of his life Kepler studied and taught Mathematics. When he was 23 years old, Kepler became an official calendar marker. Calendar making was difficult job because certain holy days had to happen just as a particular star was in a particular spot in the sky. It took a lot of complicated Maths to make a good calendar. In 1597 Kepler published his first important work, the Cosmographic Mystery. Kepler’s book explained the distance of the planets from the Sun. Kepler also said that all the planets revolve around the Sun and that the Sun remains in one position an idea built on those of the earlier astronomer Nicolas Copernicus. In1600Kepler moved to Prague, where he soon became Emperor Rudolf II’s imperial mathematician, the most important Mathematics post in Europe. Kepler discovered that Mars orbit is an ellipse (an oval-like shape) rather than a circle. He also explained important laws for the motion of all of the planets around the Sun. Kepler’s scientific work focused on astronomy. But he also studied other sciences and mathematics so he could learn everything possible about the stars.