The stars, the moon, and the shadowed earth: Viennese astronomy in the fifteenth century

This dissertation is a study of astronomy at the University of Vienna from the beginning of the fifteenth century through the career of Johannes Regiomontanus (d. 1476), the university's most celebrated astronomer. Regiomontanus and his mentor Georg Peurbach (d. 1461) established a framework for the practice of astronomy, including the linkage of cosmology to astronomy, attempts to correct the errors and ambiguities of the medieval astronomical tradition, a renewed interest in Ptolemy's Almagest, and a program of observations intended as a basis for the reform of planetary tables and models, that remained in place for the more celebrated astronomical achievements of the following century. This study traces the roots of this framework to astronomical teaching at the University of Vienna in the first half of the fifteenth century, as well as its expansion by Regiomontanus as he moved from Vienna to Italy, Hungary, and Germany.; Chapter One provides background for the reader unfamiliar with medieval, Ptolemaic astronomy, and also argues that the shift described in the next chapter was, in part, motivated by astrological concerns. Chapter Two demonstrates that, by the middle of the fifteenth century, Viennese astronomy had come to incorporate a significant element of Aristotelian cosmology. Chapter Three examines fourteenth- and fifteenth-century responses to the Theorica planetarum, the most common astronomical teaching text at medieval universities, arguing that university astronomers were capable of identifying and addressing problems with the Theorica in a sophisticated manner. Chapter Four argues that the seemingly contradictory aspects of Regiomontanus's astronomical career can be understood as all contributing to a program of reform that encompassed both the correction of astronomical tables on the basis of new and comprehensive observations as well as the construction of homocentric planetary models to replace the venerable Ptolemaic system. Chapter Five shows that Regiomontanus, in order to promote and carry out his program of reform, borrowed humanist rhetorical and critical techniques, navigated a variety of patronage environments, and capitalized on the new technology of print, establishing a vision of mathematics as on par with, and amenable to the same critical techniques as, the core humanist disciplines.