De Sphaera mundi by Johannes de Sacrobosco

Contained in this manuscript is the basic introduction to the principles of medieval astronomy, De Sphaera mundi. The text was composed in the first part of the thirteenth century by the Englishman Johannes de Sacrobosco (John of Holywood in English) who was an influential scholar, writer and monk working at the University of Paris. The immense popularity and use of this text in the medieval period is evident from the fact that it has survived in hundreds of manuscript copies, and it seems to have been the most successfully received textbook on astronomy of the time, and even in centuries that followed. Its contents are based on both Ptolemy's work and Islamic astronomy. While its primary focus is on the structure and working of the universe, Sacrobosco describes the Earth as a sphere, which goes against the popular misconception (and modern invention) that medieval society believed the world to be flat.