کلیدواژهها
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Medieval Astronomy, Islamic Astronomy, Middle East, Mumtaḥan Zīj, Star
Table, Yaḥyā b. Abī Manṣūr, Ibn al-A‘lam, Īlkhānī Zīj, Ibn Yūnus
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چکیده
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The table of 24 stars in one of the two extant manuscripts of the Mumtaḥan
zīj is the earliest non-Ptolemaic star table in medieval Middle Eastern astronomy. Dated to
829 AD, it is a fruit of the two systematic observational programs carried out by a group of
astronomers in Baghdad and Damascus in the early ninth century. In this study, the accuracy
of this table is examined, showing the existence of an obvious systematic negative error in
the longitude values. The manuscripts also contain another table of 18 stars, all of which
also appear in the first table, in which the longitudes are updated for 1011 AD. This table is
further updated for 1231 AD in the Īlkhānī zīj, the official product of the observational
programs in the Maragha observatory, northwestern Iran, in the 1260s, where it is ascribed
to Ibn al-A‘lam (d. 985 AD). In this paper, some verifiable and convincing proofs are provided
for the hypothesis that the second Mumtaḥan star table is quite probably a refinement
of the first table made by Ibn al-A‘lam on the basis of a few stellar observations by himself
dated to about 976 AD. Firm evidence for one of these observations, namely of Regulus (α
Leo), is provided by his younger contemporary Ibn Yūnus (d. 1009 AD).
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