Hypotheseis ton planomenon

work by Ptolemy

Also known as: “Planetary Hypotheses”

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June 29, 2026

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The Hypotheseis ton planomenon (Planetary Hypotheses) is a work by Ptolemy that describes his mathematical model of the universe. This model, known as the Ptolemaic system, is a geocentric cosmology, meaning it assumes the Earth is stationary at the center of the universe.12

Ptolemy's system explained the observed irregular paths of the Sun, Moon, and planets by combining several regular circular motions. This model successfully accounted for planetary movements and was widely accepted until the 16th century, when it was superseded by heliocentric models. Ptolemy's work represented a culmination of Greco-Roman science and significantly influenced medieval astronomy.134

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Ptolemy
Astronomer
…much as a later treatise, Hypotheseis tōn planōmenōn (Planetary Hypotheses). In this work he proposed what is now called the Ptolemaic system—a unified system in which each heavenly body is attached to its own sphere and the set of spheres nested so that it extends without gaps from Earth to…
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…much as a later treatise, Hypotheseis tōn planōmenōn (Planetary Hypotheses). In this work he proposed what is now called the Ptolemaic system—a unified system in which each heavenly body is attached to its own sphere and the set of spheres nested so that it extends without gaps from Earth to…
Read More

astronomy
Ptolemy
…a speculative cosmological work, the Hypotheseis ton planomenon (Planetary Hypotheses), in which he took the eccentric-and-epicycle astronomy of the Almagest as physically true. However, to give a satisfactory image of the cosmos, he needed the nested-spheres cosmology of Eudoxus. The eccentrics and epicycles were regarded as the equator circles of…
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…a speculative cosmological work, the Hypotheseis ton planomenon (Planetary Hypotheses), in which he took the eccentric-and-epicycle astronomy of the Almagest as physically true. However, to give a satisfactory image of the cosmos, he needed the nested-spheres cosmology of Eudoxus. The eccentrics and epicycles were regarded as the equator circles of…
Read More