Sacrobosco

Some of the most well known, influential textbooks used by scholars during the middle ages were authored by a man we know very little about. Johannes de Sacrobosco was probably English, though there is little evidence to support this claim.

For all the mystery surrounding the man, the legend his work has created is astonishing. He was a mathematician, with a flair for geometry, by the same token, he was an astronomer with a true gift for the mathematical computations that make much of modern astronomical study possible. Additionally, Sacrobosco is associated with some of the most iconic items in the astronomical community – the armillary sphere, the astrolabe and the humble sundial.

Sacrobosco's Work

Though little is known about the man himself, his work is widely acknowledged, recognised and understood to be some of the most significant in the field. Sacrobosco wrote four well-known books, which went on to serve as textbooks for great minds in a variety of sciences for over four centuries.

De Sphaera, Algorismus and Compotus are just three of the titles by Sacrobosco that proved popular with scholars from a variety of fields. Surprisingly, many copies of these works still exist today – allowing those able to access the tombs a unique glimpse into the past and perhaps even insight as to how that history has shaped the world today. He was critical of the Julian calendar, put forth the concept of latitude and thoroughly discussed two versions of the quadrans vetus, or old quadrant. Some surviving copies of Sacrobosco's works feature notes from scholars and lecturers of the period.

The Legacy of Sacrobosco's Work

As his texts were so widely studied, it should be no surprise to learn that Sacrobosco's legacy in the astronomical community is titanic. His books were reprinted through the seventeenth century, and often, the editions were expanded to include additional diagrams and postulations provided by his devotees.

Contrary to what many may think, Sacrobosco did not actually construct an armillary sphere – nor did he draw plans for one. However, he did make specific reference to the astrolabe, and set out instructions for making a quadrant. Sacrobosco's treatise De Sphaera made crafting accurate armillary spheres a less daunting task, as the four chapters of the book set out clear parameters for the structure of the universe, the rotation of the heavens, motion of planets and even the climates of the earth.

For those with an appreciation of the sundial, Sacorobosco's work, Tractatus de Quadrante, provides an interesting look at the technical aspects of building a quadrans vetus – an 'old quadrant'. The text discusses two variations on the instrument, both useful in finding the time. One was to be used in conjunction with tables that helped the user calculate the altitude of the noontime sun. The other, more advanced quadrant, featured a scale that indicated the solar altitude.