Claudius Ptolemy was born in Egypt in about 85 A.D. He was one of the most infuential Greek astromomers, geographers and mathematicians of his time.He had access to knowledge left by the great scientists before him.
Of the many written works of Ptolemy, the Almagest and the Geography are the best known. Almagest is still in use today. Divided into 13 sections, each section deals with a different astronomical concept. As Ptolemy continued to study and observe the heavens, he formulated his geocentric theory (Earth Centered) known as the Ptolemaic System. The Ptolemaic System shows the Earth as the center of the system followed outward by the moon, Mercury, Venus, Sun, Mars, Jupiter and Saturn. This system was accepted by all until 1543 when Nicholaus Copernicus discovered the heliocentric (sun centered)system.
For his accomplishments, Ptolemy has both a Mars crater and a lunar crater named for him.