The Greek astronomer, astrologer, and geographer Claudius Ptolemy (ca. 100-ca. 170) established the system of mathematical astronomy that remained standard in Christian and Moslem countries until the 16th century.

Ptolemy is known to have made astronomical observations at Alexandria in Egypt between 127 and 141, and he probably lived on into the reign of Marcus Aurelius (161-180). Beyond the fact that his On the Faculty of Judgment indicates his adherence to Stoic doctrine, nothing more of his biography is available.

The Almagest

The earliest and most influential of Ptolemy's major writings is the Almagest. In 13 books it establishes the kinematic models (purely mathematical and nonphysical) used to explain solar, lunar, and planetary motion and determines the parameters which quantify these models and permit the computation of longitudes and latitudes; of the times, durations, and magnitudes of lunar and solar eclipses; and of the times of heliacal risings and settings. Ptolemy also...