 Before concluding his theology studies at Tübingen, in March/April 1594 Kepler accepted an offer to teach mathematics as the successor to Georg Stadius at the Protestant school in Graz (in Styria, Austria). During this period (1594–1600), he composed many official calendars and prognostications and published his first significant work, the Mysterium Cosmographicum (= MC), which catapulted him to fame overnight. On April 27, 1597 Kepler married his first wife, Barbara Müller von Mühleck. As a consequence of the anti-Protestant atmosphere in Graz and thanks also to the positive impact of his MC on the scientific community, he abandoned Graz and moved to Prague in 1600, to work under the supervision of the great Danish astronomer Tycho Brahe (1546–1601). His first contact with Tycho was, however, extremely traumatic, particularly because of the Ursus affair (see below Section 4.1). After Tycho’s unexpected death on October 1601 Kepler succeeded him as Imperial Mathematician. During his time in Prague, Kepler was particularly productive. He completed his most important optical works, Astronomiae pars optica (=APO) and Dioptrice (=D), published several treatises on astrology (De fundamentis astrologiae certioribus, Antwort auf Roeslini Diskurs; Tertius interveniens), discussed Galileo’s telescopic discoveries (Dissertatio cum nuncio sidereo), and composed his most significant astronomical work, the Astronomia nova (=AN), which contains his first two laws of planetary motion.