Brahe, Tycho

Brahe, Tycho (1546–1601)Danishastronomer. He was the most accomplished observer of the pre-telescope era, expert in constructing instruments for making accurate naked-eye positional measurements. He first gained fame through his report (De nova stella, 1573) of the 1572 supernova in Cassiopeia. In 1576 he constructed Uraniborg, an observatory on the island of Hven in the Baltic (a second observatory, Stjerneborg, was built in about 1584). He calculated that the comet seen in 1577 had a highly elongated orbit, which would pass through several of the ‘spheres’ on which the planets were supposedly carried, and this led him to doubt the reality of Aristotle's planetary model. However, he rejected the heliocentric system proposed by Copernicus. In the Tychonic system, although the planets orbit the Sun, the Sun itself (and the Moon) revolve around a stationary Earth. Tycho made major contributions to the study of the Moon's orbit. In 1597 he moved to Prague, and employed J.Kepler as his assistant. Kepler later made use of Tycho's observations when deriving his laws of planetary motion.