How did the Tychonic system combine ideas from Ptolemy and Copernicus?

The Tychonic system, proposed by Tycho Brahe in 1583, functioned as a hybrid model that integrated elements from both the Ptolemaic system and the Copernican system.1

• From Ptolemy: Brahe retained the geocentric principle that Earth remains fixed at the center of the universe. In this scheme, both the Sun and the Moon revolve around the Earth, and an outer sphere of fixed stars rotates daily around the Earth.12
• From Copernicus: Brahe adopted the heliocentric arrangement for the remaining planets, which he held to be revolving around the Sun.12

By positioning the planets around the Sun while keeping the Sun in orbit around the Earth, the Tychonic system successfully explained the observed phase variations of Venus—a phenomenon the traditional Ptolemaic model could not account for. While mathematically equivalent to the Copernican model, it remained geocentric and is considered physically incorrect.12