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((short description|Book by Sacrobosco))
((italic title))
((refimprove|date=August 2020))
[[Image:Sacrobosco Lunar eclipse.jpg|thumb|A [[volvelle]] from a sixteenth-century edition of [[Johannes de Sacrobosco|Sacrobosco]]'s ''De Sphaera'']]
'''''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 Revolution|Copernican]] astronomy in Europe.

==Reception==
Sacrobosco's ''De sphaera mundi'' was the most successful of several competing thirteenth-century textbooks on this topic. It was used in [[university|universities]] for hundreds of years and the [[manuscript]] copied many times before the invention of the [[printing press]]; hundreds of manuscript copies have survived. The first printed edition appeared in 1472 in [[Ferrara]], and at least 84 editions were printed in the next two hundred years. The work was frequently supplemented with commentaries on the original text. The number of copies and commentaries reflects its importance as a university text.<ref>Olaf Pedersen, "In Quest of Sacrobosco", ''Journal for the History of Astronomy'', 16 (1985): 175-221.  Pedersen identifies 35 printings in Venice, another 35 in Paris, and more in 14 other cities throughout Europe.</ref>

==Content==
The 'sphere of the world' is not the earth but the heavens, and Sacrobosco quotes [[Theodosius of Bithynia|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 (planet)|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 [[North Pole|Arctic]] and [[South Pole|Antarctic poles]], the other of the inferior spheres at 23° in the opposite direction on their own axes.((fact|date=August 2020))

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 '[[Aether (classical element)|fifth essence]]' by the philosophers. All are mobile except heavy earth which is the center of the world.((fact|date=August 2020))

===The universe as a machine===
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 [[Age of Enlightenment|Enlightenment]].<ref>((cite book | first = Edward | last = Grant | title = A Source Book in Medieval Science | location = Cambridge | publisher = Harvard University Press | year = 1974))</ref>((Rp|465|quote=John of Sacrobosco is quoted in this reference.))

===Spherical Earth===
[[Image:Sacrobosco-1550-B3r-detail01.jpg|thumb|upright=1.2|Picture from a 1550 edition of ''De sphaera'', showing how the curvature of the Earth makes the mast of an approaching ship appear first]]
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 [[Myth of the Flat Earth|Earth was flat]].<ref>((cite book | first = Jeffrey Burton | last = Russell | author-link = Jeffrey Burton Russell | title = [[Inventing the Flat Earth]] | location = New York | publisher = Praeger | year = 1991 | isbn  = 0-275-93956-1))</ref>((Rp|19, 26((hyphen))27)) 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.

==See also==
*[[Armillary sphere]]
*[[Orrery]]

==References==
((reflist))

==Sources==
* ((cite journal | last = Pedersen | first = Olaf | title = The ''Corpus Astronomicum'' and the Traditions of Medieval Latin Astronomy: A Tentative Interpretation |   pages = 59–76 | editor1-first = Owen | editor1-last = Gingerich | editor1-link = Owen Gingerich | editor2-first = Jerzy | editor2-last = Dobrzycki | journal = Colloquia Copernicana III | location =  Wrocław | publisher = Ossolineum | year = 1975 ))
* ((cite book | last = Thorndike | first = Lynn | url = http://hdl.handle.net/2027/mdp.39015025028716  | title = The ''Sphere'' of Sacrobosco and its Commentators | series = Corpus of mediaeval scientific texts sponsored jointly by the Mediaeval Academy of America and the University of Chicago ;v. 2 | location = Chicago | publisher = Univ. of Chicago Press | year = 1949 | hdl = 2027/mdp.39015025028716 ))

==External links==
* ((Commonscatinline|De sphaera mundi|''De sphaera mundi''))
* [http://www.hps.cam.ac.uk/starry/sacroarmill.html Summary of the contents of each chapter]
* [http://www.esotericarchives.com/solomon/sphere.htm Sacrobosco's ''De Sphaera'' – complete treatise in English translation]
* Book, [http://babel.hathitrust.org/cgi/pt?id=mdp.39015025028716;view=1up;seq=11 ''The ''Sphere'' of Sacrobosco and its Commentators''], by Lynn Thorndike, year 1949. Text in Latin, English translation, and commentary. 
* ((YouTube|id=xOAd-Tic7IQ|title=Treasures of the RAS: The Sphere by John of Hollywood ))
* [http://www.cppdigitallibrary.org/items/browse?advanced%5B0%5D%5Belement_id%5D=48&advanced%5B0%5D%5Btype%5D=contains&advanced%5B0%5D%5Bterms%5D=Sacro+Bosco%2C+Joannes+de%2C+active+1230.+Sphaera+mundi Selected images from ''Sphaera mundi''] From The College of Physicians of Philadelphia Digital Library
((Authority control))
[[Category:1230s books]]
[[Category:Astronomy books]]
[[Category:Astrological texts]]
[[Category:13th-century books in Latin]]
[[Category:Treatises]]
[[pt:Johannes de Sacrobosco]]

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