Almagest is the Arabic name of an astronomical/astrological treatise proposing the complex motions of the stars and planetary paths, originally written in Greek as Hè Megalè Syntaxis by Ptolemy of Alexandria, Egypt, sometime around the 2nd century. Its geocentric model was accepted as correct for over a thousand years in Arabic and European societies.

The first translations into Arabic were made in the 9th century, with two separate efforts, one sponsored by the caliph Al-Ma'mun. By this time, the work was lost in Europe, or only dimly remembered in astrological lore. Consequently, Western Europe rediscovered Ptolemy from translations of Arabic versions. In the twelfth century a Spanish version was produced, later turned into Latin under the patronage of Emperor Frederick II. Another Latin version, this time directly from the Arabic, was produced by Gerard of Cremona, who found his text in Toledo in Spain. Gerard of Cremona was unable to translate many technical terms, even retained the Arabic Abrachir for Hipparchus.

In the 15th century, a Greek version appeared in Western Europe, and Johannes Müller, better known as Regiomontanus, made an abridged Latin version at the instigation of the brilliant Greek churchman Johannes, Cardinal Bessarion. At the same time, a full translation was made by George of Trebizond. It included a commentary that was as long as the original. The work of translation, done under the patronage of Pope Nicholas V was intended to supplant the old translation. The new manuscripts were a great improvement; the new commentary was not, and aroused much heated criticism. The Pope declined the dedication of the translation, and Regiomontanus' translation had the upper hand for the next century and more.

• Commentaries on Almagest were written by Theon of Alexandria (extant), Pappus (fragments), and Ammonius (lost).

External links

• On-Line copy of the Almagest's star catalog