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Pages from 1550 Annotazione on Sacrobosco's De sphaera mundi, showing the Ptolemaic system. In the Ptolemaic system, each planet is moved by a system of two spheres: one called its deferent; the other, its epicycle. The deferent is a circle whose center point, called the eccentric and marked in the diagram with an X, is distant from the Earth.
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A gorgeous picture and the best available old illutration of the Ptolemaic geocentric model of the Universe. Articles this image appears in Geocentric model, Bartolomeu Velho Creator Bartolomeu Velho (? - 1568). Photo by Joaquim Alves Gaspar. Support as nominator Alvesgaspar 12:37, 7 March 2008 (UTC)
Nederlands: The Ptolemaic system is an ancient astronomical model that posits the Earth as the center of the universe, with the planets, the Sun, and the stars orbiting around it in a series of concentric circles.
One scheme of the celestial spheres. The total number of celestial spheres was not fixed. In this 16th-century illustration, the firmament (sphere of fixed stars) is eighth, a "crystalline" sphere (posited to account for the reference to "waters ... above the firmament" in Genesis 1:7) is ninth, and the Primum Mobile is tenth.
In the Hipparchian, Ptolemaic, and Copernican systems of astronomy, the epicycle (from Ancient Greek ἐπίκυκλος (epíkuklos) 'upon the circle', meaning "circle moving on another circle") [1] was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets.
A simple illustration showing the basic elements of Ptolemaic astronomy. It shows a planet rotating on an epicycle which is itself rotating around a deferent inside a crystalline sphere. The center of the system is marked with an X, and the earth is slightly off of the center.
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