Nicolaus Copernicus’s claim that the sun was the center of the universe, first articulated in a manuscript circulated early in the sixteenth century, now known as the Commentariolus, and elaborated in his 1543 work On the Revolutions, has loomed large in the historiography of the West for initiating what is commonly called the scientific revolution. Yet we have few sources that suggest what led to this claim. This has resulted in much speculation about the cause: historians have suggested, for example, opposition to Ptolemy’s use of mathematical fictions, uncertainty about the order of the planets, and support of Aristotelian physics. The editors of this volume, which contains papers from a 2009 workshop in Montreal looking at a variety of developments during the period prior to the appearance of the Commentariolus, decry the attempt of scholars “to reduce the ‘Copernican question’ to one of finding the univocal explanation that somehow supersedes all others” (5) and seek a broader outlook.

Christopher Celenza concentrates on the importance of travel in the fifteenth century. The Polish Copernicus spent seven formative years in Italy, which exposed him to new contacts and ideas. Not only did he live and work with the astronomer Domenico Maria Novara in Bologna, but Celenza points out that the curriculum there encouraged questioning authority. Edith Dudley Sylla, on the other hand, focuses on the intellectual background to the study of astronomy in Cracow, where Copernicus first attended the university. Georg von Peurbach’s Theoricae novae planetarum from the mid-fifteenth century was the principal textbook of astronomy, but Sylla shows how much it had in common with Abū ‘Alī al-Ḥasan ibn al-Haytham (Alhazen)’s eleventh-century work On the Configuration of the World. Michael Shank looks at Peurbach’s collaborator Regiomontanus, who finished the very influential Epitome of the Almagest; he emphasizes astronomical controversies in the second half of the fifteenth century and, in particular, Regiomontanus’s hope for a cosmology of concentric spheres without the Ptolemaic complexities. Raz Chen-Morris and Rivka Feldhay treat the issues of appearances and of the visible and invisible in the work of Leon Battista Alberti and Nicholas of Cusa, which could have led Copernicus to accept the earth’s motion.

It is not surprising that a volume coedited by Jamil Ragep would emphasize the continuing influence of the Islamic world beyond the period preceding the twelfth-century translations into Latin acknowledged by Copernicus. Even Sylla, whose chapter concentrates on golden age astronomy, claims that the cessation of translations “does not mean that other modes of transmission had to end, let alone that astronomical activity in Islamic areas ceased to progress because European interest in it declined” (47). Indeed, Sally Ragep shows how vibrant the practice of astronomy in the fifteenth-century Islamic world was: she finds 489 surviving treatises by 203 authors on many facets of its study despite subsequent upheavals and invasions. But do those numbers mean that such studies found their way to Christian Europe? Nancy Bisaha notes that cross-cultural exchanges continued, but the hostility of Christian Europe toward Islam impeded acknowledgment of debt to Islamic contributions. Robert Morrison shows how Jews were important intermediaries between the Islamic world and Christian Europe in the fifteenth century. Learned Jews connected the West with the Ottoman Empire, and the Judeo-Arabic astronomical text The Light of the World by Joseph ibn Naḥmias contained ideas and techniques from Islamic astronomers and was known among Renaissance astronomers. This work contains a figure similar to the form of the Ṭūsī couple used by Copernicus. Jamil Ragep uses the two different forms of the Ṭūsī couple, a combination of circles to illustrate epicyclic motion formulated by the thirteenth-century astronomer Naṣir al-Din al-Ṭūsī, to trace the movement of the figure around the Islamic and Christian worlds and to bolster the claim that Christian scholars were borrowing from more recent Islamic work.

In presenting different aspects of the fifteenth century, the authors in this volume have enriched our understanding of the cultural milieu of the fifteenth century and astronomy’s place in it. They have suggested new and different ways to approach the problem of the path to the heliocentric universe.