Derivation of the inclination of mars’ orbit in the Almagest

Abstract

Ptolemy published the inclination of Mars’ orbit as 1.0° in the Almagest, which is smaller than the actual value of 1.9°. It is suggested that such a small value was obtained using inappropriate procedures from two values of the observed ecliptic latitudes of Mars that had errors of ~0.3°, and it is shown that a more precise value could have been obtained from the same observational values using another procedure.