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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.
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.
Reigning for 275 years, the Ptolemaic was the longest and last dynasty of ancient Egypt from 305 BC until its incorporation into the Roman Republic in 30 BC. [ 6 ] [ 7 ] Ptolemy , a general and one of the somatophylakes (bodyguard companions) of Alexander the Great , was appointed satrap of Egypt after Alexander's death in 323 BC.
The geocentric Ptolemaic system was the prevailing theory until the 16th century when Nicolaus Copernicus, and subsequently Johannes Kepler and Galileo Galilei, proposed a heliocentric system. This is one of the most famous examples of epistemological rupture in physical cosmology.
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Download as PDF; Printable version; ... move to sidebar hide. Ptolemaic is the adjective formed from the name Ptolemy, and may refer to: ... Ptolemaic system, ...
The basic elements of Ptolemaic astronomy, showing a planet on an epicycle (smaller dashed circle), a deferent (larger dashed circle), the eccentric (×) and an equant (•). Equant (or punctum aequans ) is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of the planets.
The Dialogue Concerning the Two Chief World Systems (Dialogo sopra i due massimi sistemi del mondo) is a 1632 Italian-language book by Galileo Galilei comparing the Copernican system with the traditional Ptolemaic system. It was translated into Latin as Systema cosmicum [1] (Cosmic System) in 1635 by Matthias Bernegger. [2]