Claudius Ptolemy

Claudius Ptolemy was one of the greatest and most influential astronomer and geographer of his time.  His geocentric form lasted for 1400 years.  He was born ca. 100 AD in Ptolemais Hermeii, Egypt.  His areas of achievement were in astronomy, mathematics, and geography.  Most of Ptolemy’s work has contributed greatly in today’s society.  His work in astronomy, mathematics, and geography influenced other practitioners for over 1400 years.  It is believed that he was a descendant of Greek or Hellinized ancestors and obtained Roman citizenship as a legacy from them.  There is much more known about the age where Ptolemy lived.  He lived in the time when Rome ruled most of the Mediterranean world. 

The Greek scientist Hipparchus who worked on the geocentric theory of the universe influenced Ptolemy.  There is no doubt that Ptolemy’s work in astronomy alone lasted for more than 1400 years, until the great scientific achievements of Nicholas Copernicus and Johannes Kepler.  Ptolemy utilized the mathematical methods of trigonometry to prove that the earth was a sphere and went on to postulate that the heaven s were also spheres and moved around and immobile earth in the center of the solar system.

Ptolemy’s contribution to mathematics was even more significant.  Hipparchus had invented spherical and plane trigonometry for the use of astronomers.  Ptolemy then perfected this brand of mathematics so that the theorems that he and Hipparchus created formed the basis of trigonometry.

The Almagest was used in trigonometry to measure the positions of the sun, earth, moon, and planets, and was later translated into Arabic and then Latin.  His book written after the Almagest was modeled after the work of Marinus of Tyre.  Ptolemy was the first geographer the write the “parallels of latitude” and the “meridians of longitude”.

Ptolemy’s geography is restricted to mathematical calculations, he did not write about the physical attributes of the countries he charted or the people who inhabited them.  His tables, stating the location of places in terms of latitude and longitude, gave a false impression of precision. 

In a book called Analemma he discussed methods of finding the angles needed to construct a sundial, which involves the projection of points on the celestial sphere.  In Planisphaerium he is concerned with stereographic projection of the celestial sphere onto a plane.