The Ptolemaic system is an ancient astronomical model developed by the Greek astronomer Claudius Ptolemy in the 2nd century AD. It posits that the Earth is at the center of the universe, with the Sun, Moon, planets, and stars revolving around it in circular orbits. This geocentric view was widely accepted for many centuries. In the Ptolemaic system, each celestial body moves in a small circle called an epicycle, which itself moves along a larger circle called a deferent. This complex model aimed to explain the observed movements of the planets and was influential until the Copernican revolution introduced the heliocentric model, placing the Sun at the center.