The Danish astronomer Tycho Brahe (1546-1601) carried pretelescopic astronomy to its highest perfection and tried to steer a middle course between the Ptolemaic and the Copernican systems.
Tycho Brahe, referred to by his first name, was born on Dec. 14, 1546, the son of the governor of Helsingborg Castle. His upbringing and education were entrusted to his uncle, Joergen, a vice admiral. When only 13, Tycho began attending classes of rhetoric and philosophy at the University of Copenhagen, but almost immediately he was seized with a frustration which had to do with astronomy. It was the discrepancy between the predicted and observed time of a partial eclipse of the sun. His whole life was to be spent on perfecting astronomical observations and theories to eliminate discrepancies of this kind.
Tycho studied at the universities of Leipzig, Wittenberg, Rostock, Basel, and Augsburg (1562-1570). On his return to Denmark he went to live with an uncle, Steen Bille, the founder of the first paper mill and glassworks in that country. He was the only one in the family to approve of Tycho's addiction to astronomy. He let Tycho set up his own observatory and received in turn help from him in the alchemy shop. On the evening of Nov. 11, 1572, Tycho spotted a new bright star near Cassiopeia. Other astronomers too soon noticed the nova, but it was Tycho who provided the best evidence with his huge sextant that the new star was as immobile as the other fixed stars.
Tycho's book De stella nova (1573) was a landmark in astronomy and secured for him a lifelong career. First came his appointment at the University of Copenhagen, then the royal patent entrusting him with the construction of the famous observatory called Uraniborg (Castle of Heavens) on the island of Hven. Shortly after this took place (1576), Tycho delivered another blow at the belief codified by Aristotle that no change could occur above the orbit of the moon. In De mundi aetherei recentioribus phenomenis (1577) Tycho proved that the great comet of 1577 had to be at least six times farther than the moon. The book also contained the famous Tychonic system of planets. There a secondary center was occupied by the sun with Mercury and Venus orbiting around it, forming a small system. The sun with its small system turned around the immobile earth fixed slightly off-center to the sphere of the fixed stars. The three other planets, Mars, Jupiter, and Saturn, orbited around both the sun and the earth, and their orbits were centered not on the earth but on the sun. The sphere of the fixed stars made a full revolution each day.
Tycho left Denmark in 1587 and moved to Prague, carrying along the records of his observations and most of his instruments. In 1600 Johannes Kepler joined him as his assistant. It fell to Kepler to prepare for publication, following Tycho's sudden death in 1601, the latter's collection of astronomical studies, Astronomiae instauratae progymnasmata (1602-1603).
The major work in English on Tycho is still the one by J. L. E. Dreyer, astronomer-editor of Brahe's works and correspondence, Tycho Brahe: A Picture of Scientific Life and Work in the Sixteenth Century (1890; repr. 1963). Less attentive to scientific questions is John A. Gade, The Life and Times of Tycho Brahe (1947), but it contains an ample and more modern bibliography. Tycho is discussed in George Sarton, Six Wings: Men of Science in the Renaissance (1957). □