عنوان مجله
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ARCHIVE FOR HISTORY OF EXACT SCIENCES
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چکیده
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This paper analyses a kinematic model for the solar motion by Qut.b al-
D¯ın al-Sh¯ır¯az¯ı, a thirteenth-century Iranian astronomer at the Mar¯agha observatory in
northwestern Iran. The purpose of this model is to account for the continuous decrease
of the obliquity of the ecliptic and the solar eccentricity since the time of Ptolemy.
Sh¯ır¯az¯ı puts forward different versions of the model in his three major cosmographical
works. In the final version, in his Tuh.
fa, the mean ecliptic is defined by an eccentric
of fixed mean eccentricity and a mean obliquity fixed with respect to the celestial
equator, and the center of the epicycle, which is inclined to the eccentric, moves on
the eccentric with an annual period. By an additional slow motion of the sun on the
epicycle, the true eccentricity of the solar deferent, defined by the annual motion of
the sun, and the sun’s extreme declination from the equator change, accounting for the
reduction of the eccentricity and the obliquity of the ecliptic since the time of Ptolemy.
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