It was perhaps too radical given deeply ingrained notions of uniform circular motion, and the obvious immobility of the Earth. Introduced epicycles, building on ideas of Apollonius of Perga. The main circle is the Deferent , upon which rotates the center of the secondary circle called the Epicycle to which the planet is affixed. The two rotate at different rates, fine-tuned to make the apparent motions as seen from the Earth come out right. Additional epicycles are added to further fine-tune the system.
Superior planets are brighter at opposition, when moving retrograde.
Placing the Earth at an eccentric away from the deferent center helps explain the observed non-uniform motions of the Sun, Moon, and Planets. In many ways, this work marks a turning point between models motivated primarily by philosophical aesthetics and models based on observations. Based at Alexandria. Elaborated on Hipparchus' geocentric system, adding extra features to better preserve the appearances. This is a very complex construction that, again, was introduced to preserve appearances, this time at the expense of the Aristotelian and Platonic ideal of Uniform Circular Motion with a slightly modified notion of uniform angular motion about the equant.