دستاوردهاي ابن سينا در اخترشناسي ادوار ميانه اسلامي

Avicennaʹs Achievments in Astronomy in Medieval Islamic periods

This paper gives a critical review of Avicennaʹs Astronomy in theoretical and observational aspects. Theoretically, it investigates his model for the prime and second motions of the heavens, which have been propounded in his Danishnama cAlaʹT as well as in al-Najat. In this model, he geometrically and with the strict insistence on the Aristotelian dogma in the configuration of the planetsʹ orbs, i.e. the application of the only uniform circular motion, explains that how the Prime Mover is pertinent to the Firmament and the minor orbs of the planets. In the second aspect, the only observational quantity measured by him, that is, his magnitude, 23°;33,30, for total declination, is mentioned, which with accompany of the other magnitudes gained by his Greek and Muslim predecessors had made him to believe in changing total declination. Another aspect of his work, that is, the synthesis of two aforementioned aspects appears in his Solar Model, described in the astronomical part of d\-Shija\ where he attempted to construct a theoretical model for the solar motion by the combination of five orbs so that it is able to justifyj the observational evidence of the change in total declination.