عنوان مجله
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JOURNAL FOR THE HISTORY OF ASTRONOMY
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کلیدواژهها
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Ibn al-Shātir, Jadīd zīj, medieval islamic astronomy, observational astronomy, star tables, stellar astronomy
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چکیده
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Ibn al-Shāṭir’s (1306–1375/1376 AD) star table in his Jadīd zīj, comprising of the equatorial
coordinates and magnitudes of 89 stars, is edited and analyzed in this paper on the
basis of the extant manuscripts going back to the late 14th and early 15th centuries.
It established a new tradition of arranging the celestial coordinates in the star tables
in Egypt and Syria after him. The right ascensions (mean absolute error MAE = 20.0′,
mean error μ = –2.8′, standard deviation σ = 29.1′) and the declinations (MAE = 21.1′,
μ = –3.2′, σ = 29.3′) are nearly of the same degree of precision. The stars in the region
RA ~ 120°–180° generally have the least errors in both declination and right ascension.
The declinations of the southern stars were measured more precisely than those of the
northern ones. The values for the declinations of the stars in the region δ ~ –30°–0°
(the middle of the sky towards the south of the horizon of Damascus) are significantly
the most accurate. A systematic northward shift can be seen in the declinations of
the southern stars. The declinations of 15 of 18 stars spreading out in RA ~ 67°–121°
show a southerly, downward shift. More than 65% of the stars have the errors in both
the declination and right ascension less than 32′. No outlier in the tabular coordinates
exceeds ±98′. Also, Ibn al-Shāṭir measured the magnitudes of, at least, a few stars:
he assigned a correct magnitude of +4 to λ Ori, a component of the star cluster in
the Orion that was considered a nebulous object in the Almagest star catalogue, and
presented more precise values for the magnitudes of α Sco, α Oph, β Cas, κ Ori, γ
Gem, and β CMi than Ptolemy and al-Ṣūfi.
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