Tycho [Tyge] Brahe (1546-1601), probably the greatest pre-telescopic astronomer. Born on 14 December 1546 in Knudstrup (Denmark) and of noble descent, he was sent by his family to study in Copenhagen, then to Leipzig to study Law, but he soon became entirely occupied with astronomy. In 1565 and 1566 Tycho studied mathematics at the universities in Wittenburg and Rostock. It is in Rostock that Tycho engaged in a duel with a fellow student and nobleman, that ended up costing him part of his nose.
Tycho's reputation as an accomplished astronomer rose quickly, primarily through his observations of and writings on the 1572 Novae in Cassiopea, and of the 1577 comet. Tycho demonstrated, perhaps more convincingly than anyone before him, the falsity of the Aristotelian doctrine of the immutability of the Heavens, and of the Aristotelian theory of comets as an atmospheric phenomenon taking place in the sublunar sphere.
On May 23 1576, by royal decree the Danish King Frederick II granted Tycho the island of Hven, east of Copenhagen (now part of Sweden, but a Danish possession at the time), as well as an annual stipend to further Tycho's astronomical researches. Tycho took full advantage of his independence and financial security.
He established on the island the Uraniborg Observatory. Throughout his career, and in particular at Uraniborg, Tycho proceeded to build astronomical measuring instruments of unprecedented accuracy, not to mention physical size. He also established his own printing press on Hven, and build a second underground observatory with isolated observing stations to ensure reliably independent multiple astronomical measurements.
Tycho was convinced of the falsity of the Ptolemaic/Aristotelian planetary model. Objecting to the motion of the Earth on physical and philosophical grounds, and unable to detect the annual parallax of the fixed stars predicted by the Copernican model, he rejected the latter as well and as a compromise proposed the Tychonian Planetary Model, in which the Earth is at the center of the universe, the Sun orbits the Earth, but all other planets orbit the Sun. From the point of view of planetary motions this yields predictions identical to those of the Copernican Model, without requiring annual stellar parallax.
One of Tycho's most impressive astronomical achievement was his discovery of the Moon's so-called annual variation, a variation of the Moon's orbital speed associated with the gravitational pull of the Sun, and which shows an annual periodicity due to the slightly varying distance between the Earth and Sun in the course of the year. He also determined the length of the year to an accuracy of a few seconds.
Upon losing royal support in Denmark Tycho moved to Prague and in 1598 was appointed Imperial Mathematician to the Holy Roman Emperor Rudolf II. His astronomical research program never really resumed, however. He died in Prague on October 14 1601, leaving his most recently assistant Johannes Kepler as his scientific heir.
Dreyer, J.L.E., 1890, Tycho Brahe, [Dover Reprint 1963]
Thoren, V.E. 1989, Tycho Brahe, in The General History of Astronomy, vol. 2A, eds. R. Taton and C. Wilson, Cambridge University Press, pps. 3-21.
Thoren, V.E. 1990, The Lord of Uraniborg. A Biography of Tycho Brahe, Cambridge University Press.
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