BRAHE, Tycho

(1546-1601)

The founder of modern observational astronomy, Tycho Brahe led the tran­sition from ancient to modern astronomy that occurred after the introduction of Nicolaus Copernicus's* heliocentric model of the universe. His reputation as the foremost astronomer of his day rested upon a number of cosmological dis­coveries, the establishment of a new standard for astronomical instrumentation, and a series of technical studies of the heaven's movements.

Tycho's fascination with astronomy began when he witnessed a partial eclipse on 21 August 1560. For three years thereafter, he eagerly studied astronomy and mathematics in Copenhagen until his uncle sent him to Leipzig University to broaden his studies. Rhetoric and philosophy, however, did not appeal to Tycho, and his determination to pursue astronomical studies only increased when he obtained copies of the planetary tables of King Alfonso X of Castile and the Prussian tables compiled by one of Copernicus's assistants. Tycho learned how to determine the positions of the planets using the tables and soon detected systematic errors in the data. Ill-designed instruments accounted for the discrepancies, and so Tycho compiled a table by which to correct his observa­tions. Thus by age sixteen Tycho had already learned that systematic observation coupled with improved instrumentation could reduce or eliminate inaccuracies in astronomical tables.

King Frederick II of Denmark endowed Tycho with the island of Hven and funds for building two state-of-the-art observatories known as Uraniborg or "the city of the heavens" and Stjerneborg or "the city of the stars," as well as an annual pension to support his research efforts. Tycho's most memorable cos-mological discoveries were a new, fixed star, which appeared in the constellation of Cassiopeia on 1 November 1572, and the arrival of the 1577 comet. Both the appearance of a new star and a comet running a course in the ether high above the moon ran counter to Aristotelian logic, which maintained a strict dichotomy between a changing earthly sphere and an unchanging heavenly sphere. Based on his comet studies, Tycho dismissed Aristotle's concept of solid planetary spheres. He proposed instead the Tychonic world system, an earth-centered model capable of representing all astronomical phenomena without pos­iting belief in a moving earth, for which no proof yet existed. Tycho also realized the immediate necessity of producing a new star catalog to record ce­lestial changes occurring since Ptolemy's second-century record of the heavens.

In 1581 Tycho began working on his star catalog, a ten-year project that required a plethora of specialized instruments capable of producing the most precise measurements possible. During the 1580s Tycho completed his solar theory, studies of refraction, and his lunar theory. Forced to leave Hven in 1597, Tycho moved to Prague, where Johannes Kepler* joined him as an assistant in 1600. When Tycho died in October 1601, the long-delayed star catalog was still not ready for the presses, and it was Kepler who oversaw the final publication in 1602 of his mentor's Astronomiae instauratae progymnasmata (First exercises in a Restored Astronomy).

Bibliography

V. Thoren, The Lord of Uraniborg: A Biography of Tycho Brahe, 1990.

Whitney Leeson