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date: 26 January 2021


, mathematical writer
  • G. J. Toomer
  •  and Alexander Jones


Ptolemy wrote at *Alexandria (1), between 146 ce and c.170, definitive works in many of the mathematical sciences (see mathematics), including *astronomy and *geography. Ptolemy's earliest work, the Canobic Inscription, is a (manuscript) list of astronomical constants dedicated by him in 146/7. Most of these are identical with those of the Almagest, but a few were corrected in the latter, which must have been published c.150. This, entitled μαθηματικὴ σύνταξις (‘mathematical systematic treatise’: the name ‘Almagest’ derives from the Arabic form of ἡ μεγίστη sc. σύνταξις), is a complete textbook of astronomy in thirteen books. Starting from first principles and using carefully selected observations, Ptolemy develops the theories and tables necessary for describing and computing the positions of sun, moon, the five planets and the fixed stars. The mathematical basis is the traditional epicyclic/eccentric model. In logical order, Ptolemy treats: the features of the geocentric universe and trigonometric theory and practice (book 1); spherical astronomy as related to the observer's location on earth (2); solar theory (3); lunar theory, including parallax (4 and 5); eclipses (6); the fixed stars, including a catalogue of all important stars visible from *Alexandria (1) (7 and 8); the theory of the planets in longitude (9–11); planetary stations and retrogradations (12) and planetary latitudes (13).

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