Almagest is the Latin form of the Arabic name (الكتاب المجسطي, alkitabulmijisti, in English The Great Book) of a mathematical and astronomical treatise proposing the complex motions of the stars and planetary paths, originally written in Greek as Μαθηματικἠ Σύνταξις (Mathematikē Sýntaxis, Mathematical Treatise; later titled Hē Megálē Sýntaxis, The Great Treatise) by Ptolemy of Alexandria, Egypt, written in the 2nd century. Its geocentric model was accepted as correct for more than a thousand years in Islamic and European societies through the Middle Ages and early Renaissance. The Almagest is the most important source of information on ancient Greek astronomy. The Almagest has also been valuable to students of mathematics because it documents the ancient Greek mathematician Hipparchus's work, which has been lost. Hipparchus wrote about trigonometry, but because his works have been lost mathematicians use Ptolemy's book as their source for Hipparchus' works and ancient Greek trigonometry in general.
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The date of Almagest has recently been more precisely established. Ptolemy set up a public inscription at Canopus, Egypt, in 147 or 148. The late N. T. Hamilton found that the version of Ptolemy's models set out in the Canopic Inscription was earlier than the version in the Almagest. Hence the Almagest cannot have been completed before about 150, a quarter century after Ptolemy began observing.(Reference: Introduction, Toomer's translation, Princeton University Press, 1998)
The Almagest consists of thirteen sections, called books, totalling 152 pages in a printed edition of 1515.^{[1]}
The cosmology of the Almagest includes five main points, each of which is the subject of a chapter in Book I. What follows is a close paraphrase of Ptolemy's own words from Toomer's translation.^{[citation needed]}
Ptolemy assigned the following order to the planetary spheres, beginning with the innermost:
Other classical writers suggested different sequences. Plato (c. 427 – c. 347 BC) placed the Sun second in order after the Moon. Martianus Capella (5th century A.D.) put Mercury and Venus in motion around the Sun. Ptolemy's authority was preferred by most medieval Islamic and late medieval European astronomers.
Ptolemy inherited from his Greek predecessors a geometrical toolbox and a partial set of models for predicting where the planets would appear in the sky. Apollonius of Perga (c. 262 – c. 190 BC) had introduced the deferent and epicycle and the eccentric deferent to astronomy. Hipparchus (2nd century BC) had crafted mathematical models of the motion of the Sun and Moon. Hipparchus had some knowledge of Mesopotamian astronomy, and he felt that Greek models should match those of the Babylonians in accuracy. He was unable to create accurate models for the remaining five planets.
The Almagest adopted Hipparchus' solar model, which consisted of a simple eccentric deferent. For the Moon, Ptolemy began with Hipparchus' epicycleondeferent, then added a device that historians of astronomy refer to as a "crank mechanism":^{[3]} He succeeded in creating models for the other planets, where Hipparchus had failed, by introducing a third device called the equant.
Ptolemy wrote the Almagest as a textbook of mathematical astronomy. It explained geometrical models of the planets based on combinations of circles, which could be used to predict the motions of celestial objects. In a later book, the Planetary Hypotheses, Ptolemy explained how to transform his geometrical models into threedimensional spheres or partial spheres. In contrast to the mathematical Almagest, the Planetary Hypotheses is sometimes described as a book of cosmology.
Ptolemy's comprehensive treatise of mathematical astronomy superseded most older texts of Greek astronomy. Some were more specialized and thus of less interest; others simply became outdated by the newer models. As a result, the older texts ceased to be copied and were gradually lost. Much of what we know about the work of astronomers like Hipparchus comes from references in the Almagest.
The first translations into Arabic were made in the 9th century, with two separate efforts, one sponsored by the caliph AlMa'mun. By this time, the Almagest was lost in Western 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, which was later translated into Latin under the patronage of Frederick II, Holy Roman Emperor. Gerard of Cremona translated the Almagest into Latin directly from the Arabic version. Gerard found the Arabic text in Toledo, Spain. Gerard of Cremona was unable to translate many technical terms; he even retained the Arabic Abrachir for Hipparchus.
In the 15th century, a Greek version appeared in Western Europe. The German astronomer Johannes Müller (known as Regiomontanus) made an abridged Latin version at the instigation of the Greek churchman Johannes, Cardinal Bessarion. Around the same time, George of Trebizond made a full translation accompanied by a commentary that was as long as the original text. George's translation, done under the patronage of Pope Nicholas V, was intended to supplant the old translation. The new translation was a great improvement; the new commentary was not, and aroused criticism.^{[citation needed]} The Pope declined the dedication of George's work,^{[citation needed]} and Regiomontanus's translation had the upper hand for over 100 years.
Commentaries on the Almagest were written by Theon of Alexandria (extant), Pappus of Alexandria (only fragments survive), and Ammonius Hermiae (lost).
Three translations of the Almagest into English have been published . The first, by R. Catesby Taliaferro of St. John's College in Annapolis, Maryland, was included in volume 16 of the Great Books of the Western World. G. J. Toomer's later translation, Ptolemy's Almagest, Princeton University Press, 1998 (ISBN 0691002606).^{[citation needed]} Bruce M. Perry, also a tutor at St. John's College, made the most recent translation.^{[citation needed]}
An older French translation (facing the Greek text), published in two volumes in 1813 and 1816 by Nicholas Halma, is available online at the Gallica web site [1] and [2]


