Tychonian system: Encyclopedia - Tychonian system

Tychonian system

The Tychonian system was an effort by Tycho Brahe to create a model of the solar system which would combine what he saw as the mathematical benefits of the Copernican system with the philosophical and "physical" benefits of the Ptolemaic system. It is essentially a geocentric model (with the Earth at the center of the universe), around which revolves the sun, and around the sun revolve the other planets. It can be shown through a geometric argument that the motions of the planets and the sun relative to the Earth in the Tychonian system are equivalent to the motions in the Copernican system, and the Tychonian system has the advantage of not predicting stellar parallax, which was not observable until the 19th century.

Tycho's system was foreshadowed, in part, by that of Martianus Capella, who described a system in which Mercury and Venus orbit the Sun, which orbits the Earth. Copernicus, who cited Capella's theory, even mentioned the possibility of an extension in which the other three known planets would also orbit the Sun.[1]

The Tychonian system became a major competitor with the Copernican system as an alternative to the Ptolemaic system. After Galileo's observation of the phases of Venus in 1610, most cosmological controversy then settled on variations of the Tychonic and Copernican systems. In a number of ways, the Tychonian system proved philosophically more intuitive than the Copernican system, as it reinforced commonsense notions of how the Sun and the planets are mobile while the Earth is not. Additionally, a Copernican system would suggest the ability to observe stellar parallax, which could not be observed until the 19th century. On the other hand, because of the intersecting orbits of Mars and the Sun (see diagram), it went against the Ptolemaic notion that the planets rotated within a realist notion of nested spheres.

Ultimately the Tychonian system was rejected along with the Copernican system by the observations of Brahe himself, which were used by Johannes Kepler to demonstrate that the orbits of the planets are ellipses and not circles.

In the modern era, the few who still subscribe to geocentrism use a Tychonian system with elliptical orbits. See modern geocentrism.

Categories: History of astronomy | Obsolete scientific theories

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