Ibn al-Fahhād and the great conjunction of 1166 AD (Q2313951)

Through ``experimental examination of the theories of his predecessor'' and by ``testing of the synodic phenomena as derived from the theories developed in the classical period of medieval Middle Eastern astronomy against his own observations'' Farīd al-Dīn Abu al-Ḥasan 'Alī b. al-Fahhād, in his \textit{Alā'īzīj} (1172 AD) (Greek translation in the 1290s) evaluated al-Battānī's \textit{Ṣābi' zīj} (died 929 AD) and al-Khāzinī's \textit{Sanjarī zīj} (fl. 1115 AD) predictive work regarding the conjunction between Jupiter and Saturn in 1166 AD. He found ``errors of, respectively, about 35 and 10 days in the times predicted, which are verified by a recalculation on the basis of these works and modern theories.'' He also surveyed and inspected ``the four solar theories established by his Islamic predecessors with respect to the quantitative differences between their predicted times for the occurrence of the vernal equinoxes. His calculation of the parameters of the solar and lunar eclipses in April 1176'' is found to have ``the errors of up to 1 h in the time and one digit in the magnitude.''