Kepler worked with Tycho Brahe until Brahe’s death in 1601. He succeeded Brahe as the official imperial mathematician to the Holy Roman Emperor. This position gave him access to all of Brahe’s data, including his detailed observations of Mars. He used that data to fit the orbital path of Mars using an ellipse rather than a circle. In 1604, he observed and studied a supernova, which he thought was a “new star.” At its peak, the supernova was nearly as bright as the planet Venus; today, it is known as Kepler’s supernova. Using a telescope he constructed, he verified Galileo’s discovery of Jupiter’s moons, calling them satellites. Later in his career, Kepler published a book on comets and a catalog of the motions of the planets, called The Rudolphine Tables, that was used by astronomers throughout the following century. Kepler is perhaps most famous for developing his three laws of planetary motion.