ABSTRACT
In the early thirteenth century the beginning student of astronomy had Sacrobosco's Tractatus de spera as a text to lead him through the elements of celestial motion. Sacrobosco sets out a simple and complete conceptual geometry of the heavenly bodies, wherein successive definitions of the elements of astronomy introduce all the parts of the picture in an ordered and integrative manner. Two centuries earlier at the death of Gerbert, in the age of Fulbert of Chartres and Notker Labeo of St. Gallen - there was no such text and no such clear and conceptually complete pattern of understanding. Instead the students of astronomy found the theoretical tradition represented essentially by Book VIII of Martianus Capella's De nuptiis philologiae et Mercurii and its commentaries 1 plus a set of illustrated astronomical excerpts from Pliny's Naturalis Historia. 2 These materials embedded an unintegrated and incomplete set of formal understandings in terminological preciosity and unnecessary grammatical obscurity. The wave of the future in the early eleventh century lay more with the new texts from the Arabic on the construction and use of the astrolabe than with the flawed theoretical materials of the previous two centuries. 3 Indeed, the learning involved in the mastery of these practical astrolabe texts, which required the actual drawing and manipulation of the circles and arcs of stereographic projection for stellar and planetary positions of all sorts, brought the practitioner much closer to a formal, or abstract, comprehension of heavenly motions than the astronomical texts of the preceding era. It is only in the light of the character of astronomical knowledge at the beginning of the ninth century that we can appreciate the teachings offered by the Capellan and Plinian materials and more especially by a set of astronomical diagrams added to the Plinian excerpts for instructional purposes.
