Greek astronomy

The term "planets" derives from the Greek πλανήτης, meaning "wanderer", denoting objects whose position changed relative to the stars. Because they were not as interested in divination as the Babylonians, the Greeks initially did not attach as much significance to them. The Pythagoreans, in the 6th and 5th centuries BC appear to have developed their own independent planetary theory, which consisted of the Earth, Sun, Moon, and planets revolving around a "Central Fire" at the center of the Universe. Pythagoras or Parmenides are said to have first identified the evening star and morning star (Venus) as one and the same.^[18]

In the 3rd century BC, Aristarchus of Samos proposed a heliocentric system, according to which the Earth and planets revolved around the sun. However, the geocentric system would remain dominant until the Scientific Revolution. The Antikythera mechanism was an analog computer designed to calculate the relative position of the Sun, Moon, and planets on a given date.

By the first century BC, during the Hellenistic period, the Greeks had begun to develop their own mathematical schemes for predicting the positions of the planets. These schemes, which were based on geometry rather than the arithmetic of the Babylonians, would eventually eclipse the Babylonians' theories in complexity and comprehensiveness, and account for most of the astronomical movements observed from Earth with the naked eye. These theories would reach their fullest expression in the Almagest written by Ptolemy in the 2nd century AD. So complete was the domination of Ptolemy's model that it superseded all previous works on astronomy and remained the definitive astronomical text in the Western world for 13 centuries.^[11][19] To the Greeks and Romans there were seven known planets, each presumed to be circling the Earth according to the complex laws laid out by Ptolemy. They were, in increasing order from Earth (in Ptolemy's order): the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and Saturn.