1572 (sometimes called Tycho's supernova) and the Great Comet of 1577. Relationship with Kepler In Prague, Tycho worked closely with Kepler, his assistant. Kepler was a convinced Copernican, and considered Tycho's model to be mistaken, and derived from simple "inversion" of the Sun's and Earth's positions in the Copernican model. Together, the two worked on a new star catalogue based on his own accurate positions—this catalogue became the Rudolphine Tables. Also at the court in Prague was the mathematician Nicolaus Reimers (Ursus), with whom Tycho had previously corresponded, and who, like Tycho, had developed a geo-heliocentric planetary model, which Tycho considered to have been plagiarized from his own. Kepler had previously spoken highly of Ursus, but now found himself in the problematic position of being employed by Tycho and having to defend his employer against Ursus' accusations, even though he disagreed with both of their planetary models. In 1600, he finished the tract Apologia pro Tychone contra Ursum (defense of Tycho against Ursus). Kepler had great respect for Tycho's methods and the accuracy of his observations and considered him to be the new Hipparchus, who would provide the foundation for a restoration of the science of astronomy. Illness, death, and investigations Tycho suddenly contracted a bladder or kidney ailment after attending a banquet in Prague, and died eleven days later, on 24 October 1601, at the age of 54. According to Kepler's first-hand account, Tycho had refused to leave the banquet to relieve himself because it would have been a breach of etiquette. After he returned home, he was no longer able to urinate, except eventually in very small quantities and with excruciating pain. The night before he died, he suffered from a delirium during which he was frequently heard to exclaim that he hoped he would not seem to have lived in vain. Before dying, he urged Kepler to finish the Rudolphine Tables and expressed the hope that he would do so by adopting Tycho's own planetary system, rather than that of the polymath Nicolaus Copernicus. It was reported that Tycho had written his own epitaph, "He lived like a sage and died like a fool." A contemporary physician attributed his death to a kidney stone, but no kidney stones were found during an autopsy performed after his body was exhumed in 1901, and modern medical assessment is that his death was more likely caused by either a burst