The first two paragraph of Chapter 1 of a book titled "De sphaera of Johannes de Sacrobosco in the Early Modern Period":

"Commentaries on the Sphaera of Johannes de Sacrobosco (died ca. 1256) constitute a peculiar genre in the mare magnum of medieval and early modern scientific commentaries. They are peculiar for a number of reasons. First and foremost, they do not comment on an ancient text but rather on a late medieval textbook, compiled for coursework at the University of Paris (Thorndike 1949, 76–142). Sacrobosco’s work, a short qualitative introduction to geocentric cosmology, was not ambitious in its treatment of mathematical astronomy. It is actually best defined as a manual for using a scientific instrument, namely, the armillary sphere. It is a piece of deictic writing and it was probably used for deictic teaching—its main purpose was to make students familiar with this specific instrument. A second peculiarity of these commentaries is the fact that their history of publication, the precise run of editions between the thirteenth and the mid-seventeenth century, exhibits such exceptional continuity that the usual historical periodization that divides the Middle Ages from the early modern period does not seem significant in the least.

The original text does not introduce any relevant innovation from the point of view of cosmological knowledge. It is clearly based on the geocentric conception of the universe found in Ptolemy’s Almagest, but it is also influenced by later works, especially from the Islamic scientific tradition, as Lynn Thorndike has clearly shown (Thorndike 1949, 1–75). Nevertheless, the textbook cannot be considered a simple paraphrase or abridgment, first of all because it contains a short but significant passage at the end to contextualize it in the general frame of Christian theology, and secondly because it has an original textual structure—it was designed to function in a particular context: the newly conceived university, built around the scheme of the quadrivium."

From Wikipedia:

"De sphaera mundi (Latin title meaning On the Sphere of the World, sometimes rendered The Sphere of the Cosmos; the Latin title is also given as Tractatus de sphaera, Textus de sphaera, or simply De sphaera) is a medieval introduction to the basic elements of astronomy written by Johannes de Sacrobosco (John of Holywood) c. 1230. Based heavily on Ptolemy's Almagest, and drawing additional ideas from Islamic astronomy, it was one of the most influential works of pre-Copernican astronomy in Europe.

The 'sphere of the world' is not the earth but the heavens, and Sacrobosco quotes Theodosius saying it is a solid body. It is divided into nine parts: the "first moved" (primum mobile), the sphere of the fixed stars (the firmament), and the seven planets, Saturn, Jupiter, Mars, the sun, Venus, Mercury and the moon. There is a 'right' sphere and an oblique sphere: the right sphere is only observed by those at the equator (if there are such people), everyone else sees the oblique sphere. There are two movements: one of the heavens from east to west on its axis through the Arctic and Antarctic poles, the other of the inferior spheres at 23° in the opposite direction on their own axes.

The world, or universe, is divided into two parts: the elementary and the ethereal. The elementary consists of four parts: the earth, about which is water, then air, then fire, reaching up to the moon. Above this is the ethereal which is immutable and called the 'fifth essence' by the philosophers. All are mobile except heavy earth which is the center of the world.

Sacrobosco spoke of the universe as the machina mundi, the machine of the world, suggesting that the reported eclipse of the Sun at the crucifixion of Jesus was a disturbance of the order of that machine. This concept is similar to the clockwork universe analogy that became very popular centuries later, during the Enlightenment.

Though principally about the universe, De sphaera 1230 A.D. contains a clear description of the Earth as a sphere which agrees with widespread opinion in Europe during the higher Middle Ages, in contrast to statements of some 19th- and 20th-century historians that medieval scholars thought the Earth was flat.  As evidence for the Earth being a sphere, in Chapter One he cites the observation that stars rise and set sooner for those in the east ("Orientals"), and lunar eclipses happen earlier; that stars near the North Pole are visible to those further north and those in the south can see different ones; that at sea one can see further by climbing up the mast; and that water seeks its natural shape which is round, as a drop."

De sphaera of Johannes de Sacrobosco in the Early Modern Period       (file size: about 12 MB)