Brahe (right) and Kepler discussing observations on the movement of the planet Mars. Tycho Brahe (December 14, 1546 - October 24, 1601) was a Danish astronomer. He worked to combine the geometrical benefits of the Copernican system with the philosophical benefits of the Ptolemaic system into his own model of the universe, the Tychonic system. He was the last of the major naked eye astronomers, working without telescopes for his observations. He is credited with the most accurate astronomical observations of his time, and the data was used by his assistant, Johannes Kepler, to derive the laws of planetary motion. He was exiled to Prague in 1597 and was assisted in his work by Kepler until his death in 1601 at the age of 54. Johannes Kepler (December 27, 1571 - November 15, 1630) was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his works Astronomia nova, Harmonices Mundi, and Epitome Astronomiae Copernicanae. These works also provided one of the foundations for Isaac Newton's theory of universal gravitation. He died in 1630 at the age of 58.