Knowra Almagest Almagest The Almagest is Claudius Ptolemy’s second-century astronomical treatise, presenting a geocentric cosmos through mathematical models of celestial motion and extensive observational tables.
Geocentrism : A model placing Earth at the center of the universe, with celestial bodies moving around it. The treatise organizes its account of the cosmos around Earth-centered motion.
Ptolemaic system : A geocentric astronomical system using combinations of circles to represent the motions of the Sun, Moon, and planets. It is the complete cosmological model developed through the treatise’s mathematical chapters.
Claudius Ptolemy : A second-century Alexandrian scholar whose works shaped ancient astronomy, geography, and astrology. He composed the astronomical treatise and its mathematical models.
Islamic astronomy : Astronomical scholarship developed across medieval societies under Islamic rule, drawing on Greek, Persian, and Indian traditions. Astronomers translated, criticized, and extended the Almagest’s methods and tables.
Aristotelian cosmology : A physical account of the cosmos in which Earth rests at the center and celestial bodies move in perfect spheres. It supplies a physical picture that differs from the Almagest’s chiefly mathematical treatment.
Deferent and epicycle : A geometric model in which a planet moves on a small circle whose center travels around a larger circle. These circles represent planetary paths within Ptolemy’s computational system.
Ptolemy's planetary model : A system of deferents, epicycles, and equants used to calculate the apparent motions of planets from Earth. This model accounts for planetary positions and apparent changes in speed.
Hipparchus : A Greek astronomer of the second century BCE known for star observations, mathematical astronomy, and a star catalogue. Ptolemy drew on earlier Greek observations and methods associated with Hipparchus.
Medieval European astronomy : The study of celestial motions in medieval Europe, shaped by translated ancient works and university instruction. The treatise became a central authority in medieval European astronomy.
De revolutionibus orbium coelestium : Nicolaus Copernicus’s 1543 treatise arguing for a Sun-centered arrangement of the planets. It offers a competing mathematical order for planetary motions.
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