Claudius Ptolemy was a famed Greek scholar whose work in astronomyand geometryhelped form the basis of trigonometry.Ptolemy's earliest and most famous work was the Almagest, which focused on astronomy. In it, he developed geometrical proofs, which included the first notable value for since Archimedes' time, to explain the motion of the sun, the moon, and the planets. Although his geocentric theoryof astronomy mistakenly identified the Earth instead of the sun as the center of the solar system, this work served as the authoritative text on astronomy for over 1,400 years. Ptolemy also wrote works on music, optics, and astrology. His treatise, Geography, survived for centuries as a primary reference source and included the first practical use of parallels and longitudes.

Ptolemy and his life remain a mystery outside of his scientific written works. Estimates of the era in which he lived are based on his recorded astronomical...