عنوان مجله
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JOURNAL FOR THE HISTORY OF ASTRONOMY
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کلیدواژهها
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Maragha observatory, Īlkhānī zīj, Islamic astronomy, medieval astronomy, star table,
Ptolemy, Almagest
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چکیده
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The Īlkhānī zīj compiled by Naṣīr al-Dīn al-Ṭūsī and his colleagues in the first period
of the astronomical activities (the 1260s and early 1270s) in the Maragha observatory
includes a star table collecting important observations of Islamic astronomers from the
early ninth century through the third quarter of the thirteenth century, including the
Mumtaḥan astronomers, Ibn al-A‘lam, Ibn Yūnus, as well as the Maragha astronomers
themselves. This table gives the ecliptical coordinates of 18 bright stars in comparison
with Ptolemy’s corresponding values. This medieval bright star table is especially
interesting for two reasons: first, it provides reliable evidence for the examination of the
accuracy of the observations made and the instruments employed (notably, an armillary
sphere) in the Maragha observatory. Second, it facilitates a comparative study of the
accuracy of stellar observations in medieval Middle Eastern astronomy in the period in
question. We have obtained the result that the Maragha astronomers observed more
accurate star longitudes than did their predecessors, while for the latitudes, all Islamic
observers appear to have gained about the same degree of accuracy. We also discuss
two delicate matters raised by this table: first, the problem of the use of the two
different values for the rate of precession by the Maragha astronomers in order to
convert earlier star longitudes to the epoch of the Īlkhānī zīj (1°/66 years for Ptolemy’s
longitudes and 1°/70 years for those measured by their Islamic predecessors); second,
the change in the star latitudes essentially related to the various values measured by
Ptolemy and the Islamic astronomers represented side-by-side in it. Finally, we briefly
discuss a small celestial globe designed by the son of Mu’ayyad al-Dīn al-‘Urḍī, the
instrument-maker of the Maragha observatory.
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