Theories
Geocentrism
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Geocentrism holds that Earth sits still at the center of the universe while the Sun, Moon, planets, and stars all orbit around it. Claudius Ptolemy's Almagest, completed around 150 CE, gave the model its most complete mathematical form, predicting planetary positions accurately enough that it dominated Western and Islamic astronomy for over 1,400 years. It began to give way after Copernicus published a heliocentric alternative in 1543, and lost the argument decisively once Galileo's telescope showed the phases of Venus in 1610 and nineteenth century measurements of stellar parallax directly confirmed that Earth moves.
Facts
Proposed YearSourced to the subject's own accountDated to Ptolemy's Almagest, the model's most complete and influential statement; geocentric ideas in Greek astronomy are centuries older still, so this year marks the model's definitive form, not its first appearance. Proposed BySourced to the subject's own accountClaudius Ptolemy, formalizing centuries of earlier Greek astronomy 1 Cross-Tradition Connections
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