In astronomy, the geocentric model (also known as geocentrism, or the Ptolemaic system), is the superseded theory that the Earth is the center of the universe, and that all other objects orbit around it. This geocentric model served as the predominant cosmological system in many ancient civilizations such as ancient Greece. As such, most Ancient Greek philosophers assumed that the Sun, Moon, stars, and naked eye planets circled the Earth, including the noteworthy systems of Aristotle (see Aristotelian physics) and Ptolemy.