What was the Tychonic system of the solar system?

The Tychonic system was a model of the solar system proposed by the Danish astronomer Tycho Brahe in 1583. It functioned as a hybrid between the ancient Ptolemaic system and the Copernican system.12

In this scheme, Tycho retained the geocentric view that Earth remained fixed at the center of the universe, with the Sun and Moon revolving around it. However, consistent with the heliocentric model of Nicolaus Copernicus, Tycho held that all other planets revolved around the Sun. Additionally, both the Tychonic and Ptolemaic systems maintained that an outer sphere of fixed stars revolved daily around the Earth.132

While the Tychonic model is mathematically equivalent to the Copernican system, it is physically incorrect and considered an unnecessary complication. Nevertheless, it successfully explained the observed variations in the phase of Venus, a phenomenon the Ptolemaic system could not account for.31