On the Sphere: Grosseteste’s On the Sphere was composed, we think, between 1215 and 1220. This was a turbulent period, especially in English history – for a summary listen to this podcast by Giles Gasper. Another treatise with the same name had been composed, very probably before Grosseteste’s version (although there is some scholarly disagreement on this), by another English scholar John Sacrobosco or Hollywood. Sacrobosco’s treatise deals with many, although not all, of the same themes, but in a different order and in a very different style.
While Grosseteste’s On the Sphere was popular – we have over 50 surviving manuscripts, this is well and truly eclipsed by the number of copies of Sacrabosco’s work. They may have written for different audiences, Sacrobosco’s possibly for university students (possibly at Paris, possibly at Oxford); Grosseteste’s may have been different. What this emphasises is the care needed in thinking through the treatise and its implications. We have here five talks, by expert members of the Ordered Universe, on particular aspects of the text.
First, the historical context: when was On the Sphere written, who for, and where? What were the circumstances in which it was composed. Giles Gasper introduces these questions:
Second, the structure, shape, design, and purpose of the On the Sphere. Sigbjørn Sønnesyn takes you through how to approach the text, what you should expect from the text, what knowledge does Grosseteste assume? All of these and more below.
Third, we move to the astronomical features of the treatise. A particularly interesting one, as Tom McLeish explains, is that of trepidation – something which Grosseteste takes pains to explain.
Fourth, a perceptual issue, which Grosseteste alludes to, but which Rebekah White explains in detail, the moon illusion. This is an example of how modern understanding of the phenomena described by medieval authors can help sharpen our interpretations of the past.
Fifth, an intriguing element to the treatise is the illustrations – many of the manuscript copies have single image, many have none, but a small number have complex and lavish images. Laura Cleaver takes you through these, and the wider context of visual evidence for the practice of astronomy in the Middle Ages.