The Arabic title of the astronomical work of Claudius Ptolemy (flourished 150), entitled by him μαθηματική σύνταξις, in order to distinguish it from another σύνταξις of Ptolemy's, devoted to astrology. The Almagest contains a full account of the Ptolemaic theory of astronomy, by which the retrograde movement of the inner planets was explained by a system of cycles and epicycles. It also gives, in the eighth and ninth books, a list of the fixed stars, with their positions, still of use to the astronomer. It continued to be the classical text-book of astronomy up to the time of Copernicus, and even of Newton, and was the foundation of the astronomical knowledge of the Jews (who became acquainted with it through Arabic translations) in the Middle Ages. One of the earliest Arabic translations is said to have been by an Oriental Jew, Sahl Al-Tabari (about 800), but no trace of it can be found. From Ptolemy, too, were derived the conceptions of the spheres and the primum mobile, which had so much influence upon the Cabala. The Almagest was translated into Hebrew from the Arabic, with both Averroes' and Al-Fergani's compendiums of it, by Jacob Anatoli about 1230, the latter from the Latin version of Johannes Hispalensis. Commentaries on parts of it were written by David ibn Naḥmias of Toledo, Elijah Mizraḥi, and Samuel ben Judah of Marseilles (1331); only the latter's commentary is extant. From the Almagest the Jews received their conception of the number of the fixed stars as 1,022; the comparison of the universe to an onion with its successive skins, corresponding to the spheres; and their idea of the size of the earth—24,000 miles in circumference—which indirectly led to the search for the New World, by inducing Columbus to think that the way westward to India was not so far as to be beyond his reach.
- Steinschneider, Jew. Lit. pp. 184, 186;
- idem, Hebr. Uebers. pp. 520-525;
- Neubauer, Cat. Bodl. Hebr. MSS. Nos. 2010-2013.