From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 604-605
Jūzjānī: Abū ʿUbayd ʿAbd al‐Wāḥid ibn Muḥammad al‐Jūzjānī
Flourished (Iran), 11th century
Jūzjānī was one of the earliest Islamic scientists to provide an alternative to Ptolemy's equant model. Very little is known about his life. He probably was already a jurist ( faqīh) in Jurjān when he met Ibn Sīnā in 1012. He became one of his students and tells us that he studied Ptolemy's Almagest and logic with Ibn Sīnā. He aided Ibn Sīnā with the compilation of the Cure (al‐Shifāʾ) and added the sections on geometry, arithmetic, astronomy, and music from Ibn Sīnā's earlier works to the Salvation (al‐Najāt) as well as the Philosophy for ʿAlā al‐dawla (Dānishnāme‐I ʿAlāʾī ). Jūzjānī commented on the difficult passages of Ibn Sīnā's Canon of Medicine (al‐Qānūn fī al‐ṭibb) and translated the “Book on Animals” of the Cure from Arabic into Persian. He completed Ibn Sīnā's Autobiography after his death. Jūzjānī is also the author of The Manner of Arrangement of the Spheres (Kitāb Kayfiyyat tarkīb al‐aflāk), which has not survived, as well as a surviving Summary (Mulakhkhaṣ) of this work. Finally, he is the author of Summary of the Arrangement of the Spheres (Khilāṣ tarkīb al‐aflāk), which is a commentary on Farghānī's influential Elements of Astronomy and Celestial Motions (Jawāmiʿ ʿilm al‐nujūm wa‐ʾl‐ḥarakāt al‐samāwiyya).
In his Summary of The Manner of Arrangement of the Spheres, Jūzjānī tells us of his abiding interest in astronomy and his difficulty comprehending the equant and the components of motion in latitude (inclination, twisting, and slant of the epicycle). He turned to Ibn Sīnā for guidance and was told: “I came to understand the problem after great effort and much toil and I will not teach it to anybody. Apply yourself to it and it may be revealed to you as it was revealed to me.” Jūzjānī was skeptical of Ibn Sīnā's claim for he states: “I suspect I was the first to achieve an understanding of these problems.” Jūzjānī's issue with the equant is that “we know that the motions of celestial bodies cannot be nonuniform, so that they are at times faster and at times slower. This has been demonstrated in physics (al‐ʿilm al‐ṭabīʿī).” Jūzjānī proposes to “solve” the equant problem with a model in which all spheres (the deferent, the epicycle, and a secondary epicycle) move at uniform speeds around their centers. However, the model is unworkable.
The significance of Jūzjānī's critique of the equant does not lie in his unworkable solution but rather in the fact that his contribution is independent of the critique of the equant in the work of his elder contemporary Ibn al‐Haytham entitled Doubts against Ptolemy (Shukūk ʿalā Baṭlamyūs). These represent the earliest known critiques of Ptolemy's equant hypothesis, which ultimately led to alternative models formulated by Naṣīr al‐Dīn al‐Ṭūsī and others (sometimes referred to as the “Marāgha School”) regarding planetary motion that did not resort to the equant. While Ibn al‐Haytham's critique seems to have been more influential, the Marāgha astronomers were aware of Jūzjānī's contribution. In his polemical You Did It, So Don't Blame Me! (Faʿalta fa‐lā talum), Quṭb al‐Dīn al‐Shīrāzī preserves an extensive reference to Jūzjānī's effort.
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