Danish astronomer whose accurate observations of the planets enabled German astronomer and mathematician Johannes Kepler to prove that planets orbit the Sun in ellipses. Brahe's discovery and report of the 1572 supernova brought him recognition, and his observations of the comet of 1577 proved that it moved in an orbit among the planets, thus disproving the Greek view that comets were in the Earth's atmosphere.
Brahe was a colourful figure who wore a silver nose after his own was cut off in a duel, and who took an interest in alchemy. In 1576 Frederick II of Denmark gave him the island of Hven, where he set up an observatory. Brahe was the greatest observer in the days before telescopes, making the most accurate measurements of the positions of stars and planets. He moved to Prague as imperial mathematician in 1599, where he was joined by Kepler, who inherited his observations when he died.
Brahe was born in Skåne (then under Danish rule). He studied at Copenhagen and in Germany at Wittenberg and Rostock.
Observing the 1577 comet, he came to the conclusion that its orbit must be elongated, which conflicted with the belief in planetary spheres. Brahe, the last great astronomer to reject the heliocentric theory of Copernicus, tried to compromise, suggesting that, with the exception of the Earth, all the planets revolved around the Sun.
He prepared tables of the motion of the Sun and determined the length of a year to within less than a second, necessitating the calendar reform of 1582.