The geocentric model entered Greek astronomy in the 4th century BC. During this period, educated Greeks thought that Earth was at the center of the universe and the Sun, Moon, stars and other planets surrounded Earth. But, earlier theories about the heliocentric model were completely ignored. The earliest reference to a heliocentric model of the solar system was made in the 3rd century BCE by Aristarchus of Samos! Aristarchus is also known as the “Greek Copernicus”.