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The planetary system of Ptolemy (2nd c. Α.D.)

It was the geocentric astronomical model of Ptolemy which depicted and forecasted the orbits of the Sun, the Moon and known planets on the ecliptic level. In the astronomical system of Ptolemy the Moon, Mercury, Venus, the Sun, Mars, Jupiter and Saturn revolved around the Earth, while the remainder stars stood on an outer sphere. In the present reconstruction, the three assumptions of Ptolemy have also been applied for the explanation of the apparent motion of the planets: a) the eccentricity of the Earth, b) the epicycles (which had already been proposed by Apollonius of Perga and Hipparchos for the justification of the retrograde motion of the planets) and c) the equant (the blue point from where a hypothetical observer would see the planet that revolved around him on an epicycle, covering equal angles at equal time intervals). This provident model was so precise that it dominated for 1500 years until Copernicus established, irreversibly, the previous heliocentric system of Aristarchos of Samos.