Michael H. Shank

Models and Machines in European Astronomy (13th – 15th Centuries)

When historians compare Medieval and early modern science, a favorite contrast remains the Medieval separation of astronomy and physics/natural philosophy (versus their unification in Copernicus, Kepler, or Newton, depending on the argument in question). To disrupt this excessive polarity, this paper uses brief case studies to draw attention to a thread of notable interactions between theoretical work and various forms of mechanical thinking in late-Medieval European astronomy. In several notable instances, the theoretical possibility of constructing models and sometimes the actual construction of devices emerge as recurrent concerns in late Medieval astronomy, variously as a test of physical possibility, as an embodiment of natural philosophical assumptions, or as common ground between mathematics and natural philosophy.

The translation of al-Bitrujis Principles of Astronomy in the early 13th-century was one of the first works to build a tradition eager to keep physical concerns in conversation with mathematical astronomy. For proponents and opponents alike, this work made an impact on late Medieval astronomy by focusing the debate about the origins of celestial motion and the value/existence of epicycles and eccentrics. Between the 13th through the 15th centuries, Robertus Anglicus testifies to astronomers interest in the work of clockmakers, Guido de Marchia criticizes al-Bitruji and designs an instrument intertwined with cosmological speculations about planetary rings in a fluid heaven, and Giovanni de Dondi constructs an astrarium that he sees as vindicating epicycles and eccentrics. Similar trends culminate in the work Regiomontanus. Although a mathematical astronomer who admired Ptolemy, he nevertheless criticized the Almagest for taking a two-dimensional, and therefore fictitious approach to astronomy. He hoped to eliminated epicycles and eccentrics and proposed homocentric models for the Sun and Moon, improved versions of al-Bitrujis that display mechanical sophistication. It is therefore not surprising that Regiomontanus was both building an astrarium of his own. Mechanical thinking thus constitutes a significant undercurrent across the late-Medieval spectrum of astronomy, from mathematical to natural philosophical.