The Islamic Phase of the Copernican Revolution

The story of the European adaptation of a heliocentric universe is normally told through Western astronomers; Nicolous Copernicus (1473-1543) serves as the beginning of the tale in most cases, his *De revolutionibus orbium coelestium *of 1543 hailed as a revolutionary tome. Its ideas were primarily original, or at the very least a result of Western influence. Recent work by historians such as Noel Swerdlow, Otto Neugebauer, George Saliba, and F. Jamil Ragep have challenged this interpretation, however, suggesting instead that Copernicus was heavily influenced by a sect of Islamic astronomers known collectively as the Marāgha School.[1] The evidence for such an association is formidable. Many of Copernicus’s techniques, thought processes, and mathematical proofs are strikingly similar to those of his Islamic predecessors.

The most obvious evidence linking Copernicus’s work to that of the Marāgha School exists in the mathematical strategies both use to simplify the Greek, Ptolemaic model, a goal both entities had in common. Nasir al-Din al-Tūsī (1201-1274) proved a mathematical device, known as Tūsī’s Couple, and used it to describe lunar motion (by way of generating linear motion from multiple circular motions) in his 1260-61 *Tadhkira fi ‘ilm al-hay’a. *Copernicus uses the exact same theorem — and includes a proof of it in the same format, using the same letters, as his Islamic predecessor — in *De revolutionibus. [2] *Copernicus also makes use of a mathematical technique termed ‘Urḍī’s lemma, named after its inventor, Mu’ayyad al-Din al-‘Urḍī (1200-1266), to eliminate the need to use Ptolemy’s cumbersome equants to account for planetary motion of the upper celestial spheres. Scholars hypothesize that he was exposed to this approach via some rendition or commentary on Ibn al-Shātir’s work, Shātir (1304-1375) being one of the many astronomers who utilized ‘Urḍī’s lemma in his cosmology.[3]

Additional evidence can be found in more the subtle traces of Islamic logical processes extant in Copernicus’s work. Both Copernicus and his Islamic colleagues use comets as a way to explain the possibility of a moving earth in line with observational physics, and, as F. Jamil Ragep argues in an article on the subject, Islamic sources were commenting on the possibility of a moving earth if natural philosophical epistemologies could be produced to explain the physics behind such a notion — an idea that medieval Westerners viewed as impossible.[4] Thus, the groundwork for Copernicus’s theories appear to have been lain not by his Western predecessors but by his Islamic ones.

Based on this evidence, I believe that the Marāgha School, and in particular al-‘Urḍī, al-Tūsī, and al-Shātir, belong in the narrative of the Copernican Revolution, having laid important mathematical and intellectual groundwork for the advances Copernicus and his European colleagues would expand upon. A notable impediment to this interpretation is the lack of a solid connection between Copernicus and the Marāgha School, but more work is being done to elucidate this association, and hopefully new evidence will reveal more than just a methodological link between the two parties.

[1] George Saliba, “Islamic Science and Renaissance Europe: The Copernican Connection,” *Islamic Science and the Making of European Renaissance *(Cambridge: MIT Press, 2011).

[2] George Saliba, “Islamic Science and Renaissance Europe,” 197-199.

[3] Ibid, 204-205.

[4] F. Jamil Ragep, “Tūsī and Copernicus: The Earth’s Motion in Context,” *Science in Context *14 (2001): 160.