Mirror of the Celestial Spheres: Towards Understanding Circles in Islamic Astronomy

By Maryam Patton
Submitted to Session P5928 (Towards a History and Interpretations of the "Circle" in the Scientific and Visual Cultures of the Middle East, 2020 Annual Meeting
Hist
Mediterranean Countries;
13th-18th Centuries;
LCD Projector without Audio;
In the Aristotelian cosmos, circles and spheres represented the most perfect geometrical shape in nature. All of the celestial bodies situated beyond the Earth and its orbit were understood to be made of an exalted, ethereal substance which could only move in perfect, crystalline spheres. In the third century CE, Ptolemaic cosmology devised epicycles—circles within circles—to reconcile the Aristotelian requirement of perfect spheres with the observed reality that stars and planets do not actually move this way. Since the time of Ptolemy, Islamic astronomers have grappled with Ptolemy's epicycles, improved on his models, and offered their own alternatives—such as doing away with epicycles entirely and drawing on yet another form of circular motion, the Tusi couple. In this paper I trace the history of some of the attempts made by Islamic astronomers to reconcile the notion of a circular cosmos with the reality of natural observations. This paper culminates in 17th century Ottoman accounts of astronomy, the role of geo- or heliocentrism, and the rejection and adoption of certain alternative circular cosmologies. This study also reveals how increased exposure to European astronomical developments only partially impacted Ottoman and Islamic views of the circular cosmos, who posited their own versions of circular cosmology intertwined with beliefs about the role of planetary conjunctions, astrological prognostication, and mastery over time itself.