Muḥyī al-Dīn al-Maghribī’s Measurements of Mars at the Maragha Observatory

Muḥyī al-Dīn al-Maghribī (d. 1283 AD) carried out a systematic observational programme at the Maragha observatory in northwestern Iran in order to provide new measurements of solar, lunar, and planetary parameters, as he explains in his treatise Talkhīṣ al-majisṭī (Compendium of the Almagest). His project produces a new and consistent set of parameters. On the basis of his four documented observations of Mars, carried out in 1264, 1266, 1270, and 1271 AD, he measured the unprecedented values for the radius of the epicycle, the longitude of the apogee, and the mean motion in longitude of the planet and also confirmed that Ptolemy’s value for its eccentricity was correct for his time. This paper presents a detailed, critical account of Muḥyī al-Dīn’s measurements. Using a criterion described below, we compare the accuracy of his values for the structural parameters of Mars with that of other historically important values known for these parameters from medieval Middle Eastern astronomy from the early eighth to the late fifteenth century. Muḥyī al-Dīn attained a higher degree of precision in his theory of Mars established at Maragha than the majority of his predecessors; the results were also more accurate than those established in his earlier zīj written in Damascus in 1258 AD and used in the official astronomical tables produced at the Maragha observatory, the Īlkhānī zīj