The Sphere of Sacrobosco

The Sphere of Sacrobosco is a short Latin textbook of elementary astronomy and cosmology written around 1230 by Johannes de Sacrobosco, probably an Englishman known as John of Holywood, who taught at the University of Paris. Drawing on Ptolemy and on Arabic authors such as al-Farghani, it explains in four chapters the structure of the universe as a set of concentric spheres with the earth at the centre, the sphericity of the earth, the celestial circles such as the equator, ecliptic, tropics and colures, the zodiac, the rising and setting of signs, the climates, and the motions of the sun and planets, ending with a discussion of eclipses. It became the standard introduction to astronomy in medieval and early modern universities, was the subject of many commentaries, and went through hundreds of printed editions until the seventeenth century. For the history of esotericism the Sphere is important because it provided the shared cosmological vocabulary on which astrology, astral magic and the grimoires depended: the planetary spheres, the zodiac and the timing of operations all assume its picture of the heavens. One of its commentators, Cecco d'Ascoli, was burned in Florence in 1327 partly for astrological and demonological claims in his commentary. The archive presents Lynn Thorndike's English translation from his 1949 volume The Sphere of Sacrobosco and Its Commentators. Recent work led by Matteo Valleriani has mapped the text's enormous early modern printing history.

What it contains

• Definition of the sphere and structure of the universe
• Sphericity and centrality of the earth
• Celestial circles: equator, ecliptic, tropics and colures
• The zodiac, risings and settings of the signs
• Climates of the inhabited earth
• Motions of the sun and planets and eclipses