| From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 604-605 |
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Courtesy of 
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Jūzjānī: Abū ʿUbayd ʿAbd al‐Wāḥid ibn
Muḥammad
al‐Jūzjānī
Alnoor Dhanani
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.
Selected References
Al‐Bayhaqī,
Ẓāhir
al‐Dīn (1996). Tārīkh ḥukamāʾ al‐islām. Cairo: Maktabat
al‐thaqāfa al‐dīniyya.
Gohlman, William E. (1974). The Life of Ibn Sīnā:
A Critical Edition and Annotated Translation. Albany: State University
of New York Press.
Gutas, Dimitri (1988). Avicenna and the Aristotelian Tradition.
Leiden: E. J. Brill.
Ragep, F. J. (1993).
Naṣīr al‐Dīn
al‐Ṭūsī's Memoir
on Astronomy (al‐Tadhkira fī ʿilm al‐hayʾa).
2 Vols. New York: Springer‐Verlag.
Saliba, George (1994). “Ibn Sīnā and Abū ʿUbayd
al‐Jūzjānī: The Problem of the Ptolemaic Equant.” In
A History of Arabic Astronomy: Planetary Theories during the Golden Age
of Islam. New York: New York University Press, pp. 85–112. (Originally
published in Journal for the History of Arabic Science 4 [1980]: 376–403.)
——— (1994). “Arabic
Astronomy and Copernicus.” In A History of Arabic Astronomy: Planetary
Theories during the Golden Age of Islam. New York: New York University
Press, pp. 291–305. (Originally published in Zeitschrift für Geschichte
der Arabisch‐Islamischen Wissenschaften 1 [1984]: 73–87.)
Sezgin,
Fuat (1978). Geschichte des arabischen Schrifttums. Vol. 6, Astronomie, pp. 280–281. Leiden: E. J. Brill.