Tycho BraheBorn 14 Dec 1546; died 24 Oct 1601 at age 54. Danish astronomer whose work in developing astronomical instruments and in measuring and fixing the positions of stars paved the way for future discoveries. He studied the nova of 1572 (“Tycho's star”) showed that it was a fixed star. His report, De nova...stella (1573), was taken by many as proof of the inadequacy of the traditional Aristotelian cosmology. In 1577, he moved to his own observatory on Hven Island (financed by King Frederick II). Before the invention of the telescope, using his nine-foot armillary sphere and his fourteen-foot mural quadrant, he charted the positions of 777 stars with an unparallelled accuracy. In 1599 he moved to Prague, with Johannes Kepler as his assistant.