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CONTENTS OF THE ''ALMAGEST'' The ''Almagest'' consists of thirteen books. Their subject matter can be summarized as follows:
Ptolemy's Cosmos 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.
Ptolemaic Planetary Models Ptolemy assigned the following order to the celestial spheres, beginning with the innermost: # Moon # Mercury # Venus # Sun # Mars # Jupiter # Saturn # Sphere of fixed stars Other classical writers suggested different sequences. Plato (c. 427-c. 347 BCE) made the Sun next in order after the Moon, while Martianus Capella (5th century CE) put Mercury and Venus in motion around the Sun. Ptolemy's authority was preferred by most 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 BCE) had introduced the Deferent And Epicycle and the eccentric deferent to astronomy. Hipparchus (2nd century BCE) 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. In the ''Almagest'', Ptolemy adopted Hipparchus' solar model, which consisted of a simple eccentric deferent. For the Moon, he began with Hipparchus' epicycle-on-deferent, then added a device that historians of astronomy refer to as a crank mechanism. He succeeded in creating models for the other planets, where Hipparchus had failed, by introducing a third device called the Equant . The ''Almagest'' was written by Ptolemy as a textbook of mathematical astronomy. It explained geometrical models of the planets based on combinations of circles, that 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 three-dimensional spheres or partial spheres. In contrast to the mathematical ''Almagest'', the ''Planetary Hypotheses'' is sometimes described as a book of cosmology. IMPACT OF THE ''ALMAGEST'' Ptolemy's comprehensive treatise of mathematical astronomy superceded most older texts of Greek astronomy.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 ''Almagest'' in the Middle Ages and Renaissance 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 retaining 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. Two translations of the Almagest have been published in English. The first was included in volume 16 of the Britannica Great Books series. A more recent translation, by G. J. Toomer , (ISBN 069100260600), is almost universally thought to be superior.
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