Tractatus de sphaera of Johannes de Sacrobosco
During the first half of the thirteenth century in Paris, Johannes de Sacrobosco compiled a new and original tract entitled Tractatus de sphaera. The handwritten text, of which several contemporary copies have survived, is an elementary text on geocentric cosmology. It is a simple, late medieval description of the geocentric cosmos in the form of a synthesis of the Aristotelian and Ptolemaic worldviews. The original text also inherited relevant aspects from a series of astronomic works compiled earlier by Arabic scholars, like al-Farghani and Thābit ibn Qurra.
The Sphere of Sacrobosco does not show the typical structure of a late medieval commentary: both new and older scholars are cited, but not commented on. The compilation of this treatise is in fact the consequence of an emerging intellectual need for new knowledge; it demonstrates a cultural demand that evolved during the thirteenth century for acquiring knowledge in astronomy and cosmology on a qualitative and descriptive basis, and in the framework of the university network while it was establishing itself.
Although The Sphere was not a commentary, it soon began undergoing a process of transformation by means of the practice of commenting, and it became mandatory reading in all European universities up until the seventeenth century—well beyond the publication of Nicolaus Copernicus’ De revolutionibus orbium coelestiums in 1543, which proposed a heliocentric structure of the cosmos.
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