Ptolemy

Ptolemy was one of the greatest astronomers and geographers of ancient times.("Ptolemy" 854) He lived from around 87 AD to 165 AD.("Ptolemaic System") His full name is Claudius Ptolemaeus.("Ptolemy" 854) He made his astronomical observations in Alexandria, Egypt in about 150 AD.("Ptolemy" 854)

Astronomy
Ptolemy pointed out the earth was spherical and claimed that everything in the universe moves either toward or around earth’s center ("Ptolemy" 854) According to Ptolemy, the moon, sun, planets, and stars move around the earth at various rates of speed. ("Ptolemy" 854) Ptolemy believed the stars were fixed points of light in a rotating sphere. He traced the motions of planets and worked out a theory for each of them. Ptolemy developed his system of astronomy largely from the ideas of the Greek astronomer Hipparchus. ("Ptolemaic System") His system was in use for some fourteen centuries. ("Ptolemaic System") Ptolemy’s system of astronomy was accepted as authoritative throughout Europe until 1543. ("Ptolemy" 854) Ptolemy devoted two parts of the //Syntaxis//to a catalog of the stars.(Smith 172) The Syntaxis was a scale for the stars location in the sky Ptolemy used to work with. (Smith 172) He described a mathematical arrangement of the stars and gave the celestial latitude and longitude, along with the magnitude, or brightness, for each item. (Smith 172) This catalog included 1,022 stars grouped into 48 constellations. He also discovered the irregularity of the moon in its orbit. (Smith 172)

Ptolemy’s Big Mistake
Ptolemy’s theory of the world wasn’t exactly the best. He thought all the planets in the solar system surrounded and revolved around earth’s center. ("Ptolemy" 854) Because of Ptolemy’s mistaken understanding, Christopher Columbus would later drastically underestimate the westward distance from Europe to Asia; as it turned out, there was a whole New World in between. ("Ptolemy" 855) In space, all the planets revolve around the sun and are distributed thousands of miles away from each other. Ptolemy also shared in Hipparchus’s rejection of calculations made by Eratosthenes. The latter, who was the librarian of Alexandria, had made a remarkably accurate measurement of the Earth’s size.

media type="custom" key="13417024" =Geography= Ptolemy was one of the greatest geographers of ancient times. His massive work on the subject, which summed up and corrected the work of earlier writers, offered instruction in laying out maps by three different kinds of methods of projection, provided coordinates for some eight thousand places, and treated such basic concepts as geographical longitude and latitude. During the thirteenth century, in Byzantium, Ptolemic maps were reconstructed and attached to Greek manuscripts of the text. Awhile later during the fifteenth century, a Latin translation of this text, including maps, proved a sensation in the world of book.

"Ptolemaic System." //Columbia Electronic Encyclopedia, 6Th Edition// (2011): 1. //Literary Reference Center//. Web. 22 Mar. 2012.