Ibn al-Shatir

Key Accomplishments

• Developed planetary models that eliminated the Ptolemaic equant through combinations of uniform circular motions
• Constructed mathematical models for the Moon and Mercury that closely match those later used by Copernicus
• Served as chief muwaqqit (timekeeper) at the Umayyad Mosque in Damascus
• Built an elaborate sundial for the Umayyad Mosque, considered one of the finest medieval sundials
• Advanced the tradition of non-Ptolemaic astronomy begun at the Maragheh observatory

The Full Story

Ala al-Din Abu al-Hasan Ali ibn Ibrahim ibn al-Shatir was born in Damascus in 1304 during the Mamluk Sultanate. Orphaned at a young age, he was raised by his grandfather and later apprenticed to an ivory inlayer, a craft at which he became skilled. He developed a passion for astronomy and mathematics, studying under the leading scholars of Mamluk Syria, and eventually became the chief muwaqqit (timekeeper) at the Umayyad Mosque in Damascus - a position of considerable scientific responsibility, as it involved determining prayer times and the direction of the qibla through precise astronomical observation.

Ibn al-Shatir's most significant achievement was his reform of Ptolemaic planetary theory. For over a millennium, Ptolemy's astronomical models had relied on the equant - a mathematical device that violated the principle of uniform circular motion by allowing planets to move at varying speeds around a point. This had troubled astronomers since antiquity. Building on the mathematical device known as the "Tusi couple," developed by Nasir al-Din al-Tusi at the Maragheh observatory a century earlier, Ibn al-Shatir constructed new planetary models that eliminated the equant entirely while accurately predicting planetary positions. His models achieved this through combinations of uniformly rotating circles - an elegant solution to a problem that had vexed astronomers for centuries.

The striking similarity between Ibn al-Shatir's models and those published by Nicolaus Copernicus in "De Revolutionibus" (1543) - particularly for the lunar and Mercury models - was first noticed by scholars in the 1950s and 1960s, notably E.S. Kennedy and Victor Roberts. While Copernicus placed the Sun at the center and Ibn al-Shatir retained a geocentric framework, the underlying mathematical constructions are virtually identical. The question of whether Copernicus had direct or indirect access to Ibn al-Shatir's work, possibly through Byzantine Greek intermediaries or Italian translations, remains one of the most debated questions in the history of science.

Beyond theoretical astronomy, Ibn al-Shatir was a skilled instrument maker. He constructed a magnificent sundial for the minaret of the Umayyad Mosque, the finest of its kind, and designed several innovative astronomical instruments. His work represents the culmination of a long tradition of critical revision of Ptolemaic astronomy in the Islamic world, stretching from Ibn al-Haytham's "Doubts Concerning Ptolemy" through the Maragheh school to his own solutions in Mamluk Damascus.

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Connected Figures

Sources

• [1]Saliba, George. Islamic Science and the Making of the European Renaissance (MIT Press, 2007)
• [2]Kennedy, E.S. and Victor Roberts. "The Planetary Theory of Ibn al-Shatir." Isis, Vol. 50, No. 3, 1959
• [3]Saliba, George. "Arabic Planetary Theories after the Eleventh Century." in Encyclopedia of the History of Arabic Science, Vol. 1 (Routledge, 1996)
• [4]King, David A. In Synchrony with the Heavens, Vol. 2 (Brill, 2005)