Ptolemy was Roman Citizen that lived in Alexandria, Egypt in the 2nd Century AD. He was a mathematician, astronomer, geographer, and also an astrologer. He wrote critical books that defined the world around him with the first book providing a new model for the universe called the geocentric model and other books providing geographic and astrology information.
- With all of the travel during the growing period of the Roman Empire, travelers needed to know how to navigate by the stars and the movement of the planets. Ptolemy used 800 years of past knowledge possibly from the Library in Alexandria to develop a new mathematical model of the universe which provided accurate predictions on the locations of stars and planets. This improved had Earth as a sphere that was in the center of the universe with the Sun, Moon, and all the other stars and planets revolving around the Earth.
- Ptolemy used past history to provide new information in an easy to use set of tables which allowed the reader to compute the future or past positions of the planets and constellations. He wrote that the Earth as a sphere and the also calculated the distance to the Sun and other planets using what he believed to be the radius distance of the Earth.
- Ptolemy's geocentric model and tables were used to prepare astrological charts for over 1,500 years. His work was translated into Latin and Arabic and was accepted as the standard for science until the 16th century. His model also provided the concept of elliptical orbits for the planets which mathematically enabled his tables to correctly predict future planet movements.