The Medieval Cosmos: Sacrobosco's De sphaera

Nothing is known about Johannes de Sacrobosco's early life, but it is commonly held that he was educated at Oxford and then entered the Order of St. Augustine at the Monastery of Holywood in Nithsdale, Scotland. Around the year 1220 he went to Paris, where he became professor of mathematics at the university and promoted the new classical and Arabic learning that was causing such ferment in Europe. Arabic scholars had not only preserved classical treatises on mathematics, but had developed their own simpler number system and algebra.

De sphaera, Sacrobosco's most important work, first appeared in 1220 and was used as an astronomy textbook at the University of Paris. It remained the textbook for astronomy throughout Europe for the next 450 years. This is one of the many surviving manuscript copies of the work; its gold illumination and fine vellum made it far too expensive a book for a student to own. Its representation of the medieval cosmos is characteristic of illustrations that persisted until well into the 17th century. At the center of the chart showing the solar system as concentric circles is the imperfect sphere of the Earth, surrounded by the spheres of water, air, and fire, and then the concentric circles representing the spheres of the known planets and the fixed stars. The last concentric circle represents the Primum Mobile or Prime Mover, i.e., God, the First Cause.


Johannes de Sacrobosco. Computus, Quadrans, De sphaera, Algorismus, Cautelae [Chronological Calculation, Quadrant, On the Sphere, Arithmetic, Tricks]. In Latin; hand-painting and illumination on vellum. France, ca. 1260.
The New York Public Library, Manuscripts and Archives Division.


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