page of the Almagest

Detail from Book X, Chapter 7, of a 13th century translation of the Almagest made from Arabic to Latin in Spain in 1175 by Gerard of Cremona. This image illustrates Ptolemy's kinematic model for the motion of the superior planets – Mars, Jupiter, and Saturn.

The Almagest is the Arabic title of Ptolemy's Syntaxis, the writings in which he combined his own astronomical researches with those of others. Written in about 150 AD, the Almagest covered elements of spherical astronomy, solar, lunar, and planetary theory, eclipses, and the fixed stars. Although much of the work is inaccurate, even in premise, it remained the standard reference source in Europe until Nicolaus Copernicus published his results in the 16th century.