Islamic Astronomers to whom Copernicus was indebted Refinements and limitations of the Ptolemaic system

Medieval Islamic scholars, while adhering to the geocentric Ptolemaic model, developed sophisticated planetary motion geometries that eventually contributed to the astronomical innovations of early modern Europe. However, like the theological cosmology of Christian Europe, Islamic astronomy was also deeply intertwined with a religious epistemology that regarded perfect circular orbits as evidence of a divine celestial order. The intellectual heritage of ancient Greece, transmitted through Byzantium, was translated into Syriac and Persian and, following the rise of Islam, further into Arabic. During this process, the reinterpretation of ancient texts and the integration of contemporary knowledge were transmitted to Europe through Latin translations from al-Andalus in Iberia and southern Italy. After the fall of Byzantium in 1453, astronomical knowledge translated from Arabic into Greek found its way to Renaissance Europe, exerting both direct and indirect influence on Nicolaus Copernicus. In his De revolutionibus (1543), Copernicus explicitly referenced five Islamic astronomers—al-Battani, al-Zarqālī, Ibn Qura, Ibn Rushd, and al-Bitruji—while also drawing upon the models of figures like al-Tūsī, al-‘Urḍī, and al-Shāṭir, whose influence, though unmentioned by name, is evident in his work. Particularly, Book III of De revolutionibus is dedicated to the geometric models of planetary motion developed by Islamic scholars. Thus, Copernican astronomy was not an entirely original endeavor but rather the culmination of investigations that stood on the shoulders of Ptolemy and medieval Islamic scholars. Although Copernicus introduced a simple heliocentric model in his Commentariolus (1514), his later De revolutionibus of 1543 became more complex, requiring a greater number of epicycles to address the problem of non-uniform planetary motion along circular orbits. This complexity was ultimately resolved by Johannes Kepler’s discovery of elliptical orbits, which eliminated the necessity of epicycles.