any theory of the structure of the solar system (or the universe) in which Earth is assumed to be at the centre of all. The most highly developed geocentric system was that of Ptolemy of Alexandria (2nd century AD). It was generally accepted until the 16th century, after which it was superseded by heliocentric models such as that of Nicolaus Copernicus. Compare heliocentric system; Ptolemaic system; Tychonic system.