Ibn al-Shatir

Ala al-Din Ali ibn Ibrahim ibn al-Shatir al-Ansari al-Dimashqi was born in 1304 CE in Damascus, Syria, and spent almost his entire life in that city, becoming one of the chief astronomers and timekeepers of the Umayyad Mosque. His official title was muwaqqit, or timekeeper, a position that carried responsibility for determining the times of the five daily prayers through careful astronomical observation and calculation.

Ibn al-Shatir was the last and arguably the greatest of the medieval Islamic astronomers who systematically reformed the Ptolemaic model of the universe. He was deeply troubled by the inconsistencies within Ptolemaic astronomy, particularly the use of the equant point, a mathematical device that violated Aristotelian principles of uniform circular motion. His response was to develop a new planetary model using only small epicycles and deferent circles, eliminating the need for the equant entirely.

His model of the solar system was a radical departure from Ptolemy, achieving the same predictive accuracy while using only mathematically and physically consistent mechanisms. Most remarkably, the lunar and planetary models that Ibn al-Shatir developed in the fourteenth century are mathematically identical to those later proposed by Nicolaus Copernicus in his revolutionary work of 1543. Historians of science have debated intensely how Copernicus came to use the same models, with many concluding that knowledge of Ibn al-Shatir's work reached Europe through intermediate channels.

In addition to his theoretical astronomy, Ibn al-Shatir was a master instrument maker who designed and built elaborate sundials, astronomical compendiums, and the first known universal astrolabe. He also constructed a large horizontal sundial for the Umayyad Mosque that incorporated his corrected astronomical tables. He died in Damascus in 1375 CE, leaving behind a body of work that constitutes one of the most original contributions to pre-Copernican astronomy.