Brahe, Tycho (1546–1601)

Danish astronomer. His 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 Aristotle's 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, Leipzig, and Rostock. His interest was roused by the total eclipse of 25 August 1560, and from that time he took an active interest in astronomy.

He observed the ‘new star’ that blazed forth in Cassiopeia from November 1572. It was a supernova, which was bright enough to be seen by day, and was visible for over a year. Brahe gave an account of the star in De Nova Stella (1573), in which he pointed out that his observations showed it to be further away than the Moon, and thus in those realms where, according to Aristotelian philosophy, no change could take place. He observed the bright comet of 1577, and came to the conclusion that the comet's 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 all the planets revolved around the Sun, with the exception of the Earth.

He also became aware that the actual places of the planets did not agree with their places as predicted in the current tables, and saw the need for better tables based on new observations of the motions of the Sun, Moon, and planets. He prepared tables of the motion of the Sun and determined the length of a year to within less than a second, necessitating the 1582 calendar reform. His catalogue giving the positions of about 800 stars was the first completely new one since Ptolemy's and remained in use for over a century. Johann Bayer's famous atlas was plotted from it.

Brahe built Uraniborg, ‘the City of the Heavens’, on Hven, and with his many assistants observed the Sun, Moon, stars, and planets 1576–96. He was visited there by many notable persons, including James VI of Scotland, later James I of England, who wrote a poem in his honour. Brahe left Denmark in 1597 after he had failed to retain the favour of King Frederick's successors. He found a new patron in Emperor Rudolf II and settled in the emperor's residence in Prague in 1599.