How was the Copernican model different from the Ptolemaic geocentric model?

The primary difference between the two models lies in the placement of the Earth and the Sun within the universe.

The Ptolemaic system is a geocentric model, which assumes that the Earth is stationary and located at the center of the universe, with the Sun, Moon, planets, and stars revolving around it. To account for the observed irregular movements of planets, such as retrograde motion, Ptolemy utilized a complex system of epicycles (small circular paths) and deferents (larger circular paths), along with an "equant" point to maintain uniform circular motion.12

In contrast, the Copernican system is a heliocentric model, which places the Sun at the center of the solar system. In this view, the Earth is considered a planet that orbits the Sun annually while simultaneously rotating on its own axis once every 24 hours. While Copernicus retained some of the complex geometrical apparatus of the Ptolemaic system, such as epicycles, his model offered a qualitative simplicity and a new physical reality that shifted the foundation of astronomical thought, eventually leading to the Scientific Revolution.324