This paper surveys the results established so far by the on-going research on the planetary theories in Arabic astronomy. The most important results of the Maragha astronomers are gathered here for the first time, and new areas for future research are delineated. The conclusions reached demonstrate that the Arabic astronomical works mentioned here not only elaborate the connection between Arabic astronomy and Copernicus, but also that such activities, namely the continuous reformulation of Greek astronomy, were not limited to a specific (...) group of astronomers or to a specific geographical area. It is shown that such activities were spread over a period of more than seven hundred years, from the early eleventh till the sixteenth century, and over an area stretching from the Andalusian peninsula in the west to the farthest reaches of Central Asia in the east. (shrink)

This paper presents an analysis of the systematic astronomical observations performed by Muḥyī al-Dīn al-Maghribī at the Maragha observatory between 1262 and 1274 AD. In a treatise entitled Talkhīṣ al-majisṭī, preserved in a unique copy at Leiden, Universiteitsbibliotheek, Muḥyī al-Dīn explains his observations and measurements of the Sun, the Moon, the superior planets, and eight reference stars. His measurements of the meridian altitudes of the Sun, the superior planets, and the eight bright stars were made using the mural quadrant of (...) the observatory, and the times of their meridian transit using a water clock. The mean absolute error in the meridian altitudes of the Sun is ~ 3.1′, of the superior planets ~ 4.6′, and of the eight fixed stars ~ 6.2′. The clepsydras used by Muḥyī al-Dīn could apparently fix time intervals with a precision of ± 5 min. His estimation of the magnitudes of three lunar eclipses observed in Maragha in 1262, 1270, and 1274 AD is in close agreement with modern data. (shrink)

ArgumentIn theAlmagest, Ptolemy finds that the apogee of Mercury moves progressively at a speed equal to his value for the rate of precession, namely one degree per century, in the tropical reference system of the ecliptic coordinates. He generalizes this to the other planets, so that the motions of the apogees of all five planets are assumed to be equal, while the solar apsidal line is taken to be fixed. In medieval Islamic astronomy, one change in this general proposition took (...) place because of the discovery of the motion of the solar apogee in the ninth century, which gave rise to lengthy discussions on the speed of its motion. Initially Bīrūnī and later Ibn al-Zarqālluh assigned a proper motion to it, although at different rates. Nevertheless, appealing to the Ptolemaic generalization and interpreting it as a methodological axiom, the dominant idea became to extend it in order to include the motion of the solar apogee as well. Another change occurred after correctly making a distinction between the motion of the apogees and the rate of precession. Some Western Islamic astronomers generalized Ibn al-Zarqālluh's proper motion of the solar apogee to the apogees of the planets. Analogously, Ibn al-Shāṭir maintained that the motion of the apogees is faster than precession. Nevertheless, the Ptolemaic generalization in the case of the equality of the motions of the apogees remained untouchable, despite the notable development of planetary astronomy, in both theoretical and observational aspects, in the late Islamic period. (shrink)