Tycho Brahe

1546-1601

Danish Astronomer

Tycho Brahe is considered the greatest observational astronomer of the pre-telescopic era. His observations of the 1572 nova and 1577 comet helped undermine Aristotelian cosmology, while his observations of Mars proved critical to Johannes Kepler's (1571-1630) discovery of the laws of planetary motion.

Brahe was born to aristocratic parents on December 14, 1646, at Skåne in southern Sweden (then under Danish rule). While attending the University of Copenhagen, Brahe developed an interest in astronomy after observing a partial eclipse of the Sun (1560). His newfound interest was discouraged by his paternal uncle, who sent him to study law at the University of Leipzig (1562).

Brahe secretly continued his astronomical researches, and in August 1563 he observed the conjunction of Saturn and Jupiter, noting it occurred about a month later than the Alphonsine Tables and a few days later than the Prutenic Tables predicted. He resolved to prepare more accurate tables and worked at producing improved instruments to make the necessary observations. After his uncle's death in 1565 he continued his astronomical and mathematical studies at the universities in Wittenberg, Rostock (where he lost the greater part of his nose in a dual), Basel, and Augsburg before returning to Copenhagen in 1570.

Brahe's reputation was established with the publication of De nova stella (1573), which details his observations of the nova of 1572. His measurements indicated the phenomenon was not part of the atmosphere nor was it attached to the sphere of a planet, but that it was located among the fixed stars. This undermined the prevailing Aristotelian notion that the heavens were perfect and unchanging.

In 1576 King Frederick II of Denmark granted Brahe the island of Hven and funds to construct and maintain an observatory. Brahe accepted and spared no expense in building the magnificent research facility Uraniborg (Castle in the Sky). In accordance with his desire to reform positional astronomy he equipped Uraniborg with instruments of unsurpassed accuracy. He invented new viewing sights, better instrument mounts, and improved methods for inscribing scales by transversals.

Brahe dealt another blow to Aristotelian cosmology with his observations of the comet of 1577. Because the erratic behavior of comets was incompatible with the immutability of the heavens, Aristotle (384-322 b.c.) maintained they were atmospheric exhalations. Brahe's parallax measurements indicated the comet of 1577 was more distant than the Moon. Furthermore, he concluded that its orbit was elongated, suggesting that it had passed through several planetary spheres.

Brahe rejected the Ptolemaic system as incompatible with his observations, but scripture and a lack of stellar parallax prevented him from accepting Copernican heliocentrism—the idea that Earth revolves around the Sun. As a compromise he advanced his Tychonic theory in which all of the planets but Earth orbit the Sun, with the Sun and its train of planets revolving about a stationary Earth. This system had the advantage over the Ptolemaic system of being able to account for the phases of Venus and gained acceptance in many quarters. Brahe's ability as a theorist was also revealed by his brilliant lunar theory.

Almost every astronomical measurement of importance was improved upon by Brahe during his years at Uraniborg. Unfortunately, difficulties with Frederick II's successor forced him to leave Hven in 1597. At the invitation of Emperor Rudolph II he moved to Prague in 1599. He was joined there by Johannes Kepler in 1600, but their collaboration was cut short by Brahe's death on October 24, 1601. Kepler eventually completed the Rudolphine Tables (1627) begun by Brahe, developing their theory not in accordance with Tychonism but with heliocentrism. In the process he used Brahe's data to discover the law of planetary motion.

STEPHEN D. NORTON