Almagest

The work known as the Almagest (/ˈælməˌdʒɛst/), named "Μαθηματικὴ Σύνταξις" (Mathēmatikē Syntaxis) in Ancient Greek, and also called Syntaxis Mathematica or Almagestum in Latin, is a 2nd-century Greek-language mathematical and astronomical treatise on the apparent motions of the stars and planetary paths, written by Claudius Ptolemy (c. AD 100 – c. 170). One of the most influential scientific texts of all time, its geocentric model was accepted for more than 1200 years from its origin in Hellenistic Alexandria, in the medieval Byzantine and Islamic worlds, and in Western Europe through the Middle Ages and early Renaissance until Copernicus.

The Almagest is the critical source of information on ancient Greek astronomy. It 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 appear to have been lost, mathematicians use Ptolemy's book as their source for Hipparchus's work and ancient Greek trigonometry in general.

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