Almagest

The Almagest, originally titled The Mathematical Syntaxis and attributed to Claudius Ptolemy, is a comprehensive treatise on astronomy compiled in the 2nd century CE. It became known in the Islamic world as al-Majisti and later acquired the Latinized name Almagest. The work presents a geocentric model of the heavens, detailing the probable positions and motions of the Sun, Moon, planets, and stars, and providing mathematical methods for astronomical calculation. It was the dominant astronomical authority in both the medieval and early modern periods.

Central to the Almagest is the Ptolemaic system, which explains planetary motions through a system of deferents and epicycles, with circular motions and the controversial equant to account for observed speeds. It describes retrograde motion and offers a framework for predicting celestial positions. The text also contains extensive mathematical tools, including tables of chords used for trigonometric calculations, and a star catalog listing roughly 1,022 stars with their longitudes and latitudes.

The work’s influence extends beyond its own era. It was translated into Arabic in the 9th–10th centuries, where it was studied, preserved, and often refined by Islamic astronomers. In the 12th century, Latin translations by scholars such as Gerard of Cremona reintroduced the Almagest to Western Europe, where it shaped astronomical practice for centuries and informed astrology, navigation, and scientific thought until the Copernican revolution.

Manuscripts of the Almagest survive in various forms, and it has been supplemented by related texts, including the Planetary Hypotheses in some editions. Its historical significance lies in its systematic approach to celestial mechanics and its long-standing authority in both the Islamic and Christian worlds.