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Tycho Brahe

1546 - 1601

Tycho Brahe

Tycho Brahe was a Danish astronomer, whose meticulous observations and ideas about the nature of planets, stars and comets, although erroneously accommodating rather than directly challenging the long-standing Aristotelian and Ptolemaic versions of the heavens, they were nevertheless an important contribution to the coming scientific revolution, and specifically enabled his assistant, Johannes Keppler, to derive his breakthrough laws of planetary motion.

  • Nationality
  • Danish

  • Subject
  • Astronomy

  • Fields
  • Stat mapping, planetary observations

  • Posts
  • Brahe obtained royal patronage to build an observatory, called Uraniborg (city of the heavens), on the island of Hven, Denmark, and later Stjerneborg (Star City).

    Official imperial astronomer to the Holy Roman emperor Rudolph II, in Prague. He built the observatory Benátky nad Jizerou, where he was assisted by Johannes Kepler.

  • Publications
  • De nova stella (On the new star), 1573, in which he refutes the Aristotle version of a fixed celestial realm.

  • Theories
  • Stellae Novae (now supernovae) were not sub-lunar (between the Earth and the Moon), and not comets in the atmosphere.

    Comets passed through the celestrial spheres, not the atmosphere.

    Tychonic System: a merger of the Copernican and Ptolemaic systems. Earth reigned on at the centre, the Sun revolved around the Earth, but the planets now revolved around the Sun. Here we see a generational shift, as Johannes Keppler, working with Brahe, tried to convince his master of the veracity of the Galilean/Copernican heliocentric model. With Tycho's data, Galilei's telescope, and Keppler's laws, the 17th century was primed to change the celestial model definitively, sealed and delivered with Newton's laws of motion and gravity.

    Lunar theory: variation in Moon's longitude, librations in the inclination of the plane of the lunar orbit.

  • Equations
  • Johannes Kepler used Brahe's astronomical data, particularly of the planet Mars, to derive his three laws of planetary motion.

    Tycho Brahe introduced a system of systematic correction for refraction of the atmosphere in the measurement of celestial objects. This system he published in tables.

    Prosthaphaeresis: Tycho applied an algorithm for approximating products. This system predated logarithms, and was based on trigonometric identities.

  • Experiments/Discoveries
  • Observations with the naked eye, plotting the positions of stars and planets to unprecedented accuracy, to within 1.0 to 1.5 arcminutes, and an overall mean error of 2 arcminutes.

Title page from Tabulae Rudolphinae
Title page from Tabulae Rudolphinae

Brahe made his observations before the development of the telescope for astronomical purposes (c. 1609). Using an astrolabe, he meticulously measured the positions of stars, and catalogued them. What distinguishes him from other astronomers of his and previous times were the quantity and accuracy of his observations.

Tycho Brahe
Tycho Brahe, 1546 - 1601, Danish/Swedish astronomer

He was not a champion of the Copernican heliocentric system, but did introduce modifications to the classical Ptolemy system, known as the Tychonic System. This system was 'geo-heliocentric', keeping the Earth fixed immobile at the centre of the universe, while the sun revolved around it. However, he proposed a mid-way solution in an attempt at accounting for observational discrepancies that made an immobile Earth at the centre of the universe so untenable (and complicated!), by which the planets revolved around the Sun, which helped match observations. This was more acceptable to the Church than Galileo's model based on Copernicus's Sun at the centre idea.

Tycho Brahe with King Christian IV of Denmark, 1596
Tycho Brahe with King Christian IV of Denmark, 1596

Tycho's explanation for why the Earth did not move was that it was a "lazy" body. His perception provides us with an insight into just how difficult it was, despite a lifetime of keen observation, to leave behind archaic concepts (aka Aristotle):

..such a fast motion [of sun and stars] could not belong to the earth, a body very heavy and dense and opaque, but rather belongs to the sky itself whose form and subtle and constant matter are better suited to a perpetual motion, however fast. Uraniborg, Denmark, Tycho Brahe's observatory

Uraniborg, Denmark, Tycho Brahe's observatory

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