The Ptolemaic Cosmological System

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“He is most remembered because of his development of the geocentric (Earth-centered) cosmological system, known as the Ptolemaic system or Ptolemaic cosmology, which was one of the most influential and longest- lasting, intellectual-scientific achievements in human history. Although his model of the universe was erroneous, he based his theory on observations that he and others had made, and he provided a mathematical foundation that made a powerful case in support of the geocentric paradigm and ensured its continued use well into the future. He may have been a Hellenized Egyptian. Aside from that, almost nothing is known about Ptolemy's life, family background, or physical appearance. Virtually nothing is known about Ptolemy’s life except …show more content…

However, if the path’s center is displaced from the Earth, the body will sweep out equal angles in unequal times
(again, from a terrestrial perspective), moving slowest when farthest from the Earth (apogee) and fastest when nearest the Earth (perigee). With this simple eccentric model Ptolemy explained the Sun’s varying motion through the zodiac. Another version of the model, suitable for the Moon, had the direction of the line from apogee to perigee gradually shifted.
In order to explain the motion of the planets, Ptolemy combined eccentricity with an epicyclic model. In the
Ptolemaic system each planet revolves uniformly along a circular path (epicycle), the center of which revolves around the Earth along a larger circular path (deferent). Because one half of an epicycle runs counter to the general motion of the deferent path, the combined motion will sometimes appear to slow down or even reverse direction (retrograde). By carefully coordinating these two cycles, the epicyclic model explained the observed phenomenon of planets retrograding when at perigee. Ptolemy enhanced the effect of eccentricity by …show more content…

Ptolemy was well aware that he knew about only a quarter of the globe, and he knew that his information did not extend to the Eastern Sea.
Because Ptolemy derived most of his topographic coordinates by converting measured distances to angles, his maps are distorted. His values for latitude were in error by up to two degrees. For longitude, his measures were even worse, because there was no reliable method to determine geographic longitude; Ptolemy was well aware of this. It remained a problem in geography until the invention of chronometers at the end of the eighteenth century. It must be added that his original topographic list cannot be reconstructed. The long tables with numbers were transmitted to posterity through copies containing many scribal errors, and people have always been adding to or improving the topographic data. This can be viewed as a testimony to the persistent popularity of this influential work.”

http://www.newworldencyclopedia.org/entry/Ptolemy

Ptolemy in Geometry

“Ptolemy was a first-rate geometer and mathematician who devised important new geometrical proofs

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