| From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 623-624 |
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Khafrī: Shams al‐Dīn Muḥammad ibn Aḥmad
al‐Khafrī al‐Kāshī
Glen M. Cooper
Born probably Khafr
near Shiraz, (Iran), circa 1470
Died probably (Iran),
after 1525
Khafrī
was an Iranian theoretical astronomer who produced innovative planetary theories
at a time well beyond the supposed period of the decline of Islamic science.
Little is known about his life. Various Shīʿī writers
claim Khafrī as one of their own religious scholars, and the sources
assert that he was influential in the program of the Safavid Shāh Ismāʿīl
(died: 1524) to make Shīʿism the official Islamic sect of Iran. The
fact that Khafrī wrote works in the fields of both religion and astronomy
seems to indicate that at his time and place Islamic religious scholars saw
no insuperable conflict between science and religion. This appears contrary
to the traditional view that science and religion were constantly at odds
in Islamic society, and that, long before the lifetime of Khafrī, religious
scholars effectively squelched the scientific impulse in Islam. Other examples
of Islamic scientists who also were religious scholars include Bahāʾ
al‐Dīn al‐ʿĀmilī and Niẓām
al‐Dīn al‐Nīsābūrī.
Khafrī's
fame as an astronomer rests mainly on his astronomical treatise al‐Takmila
fī sharḥ “al‐Tadhkira” (The
completion of the commentary on the Tadhkira). This was a commentary
on Naṣīr
al‐Dīn al‐Ṭūsī's important astronomical
treatise, al‐Tadhkira fī ʿilm
al‐hayʾa (Memoir on astronomy). As was the custom of the time,
in both the Arabic and Latin worlds, a scholar often presented his own theories
within the context of a commentary on the work of an esteemed author.
Consistent
with the Islamic tradition in theoretical astronomy, in which astronomers
had sought to reform Ptolemaic astronomy by revising Ptolemy's
planetary models into physically consistent forms, Khafrī presented new
models. Ptolemy had devised models of planetary motion involving spheres that
were required to rotate with nonuniform velocity with respect to poles (the
most notorious being the equant) other than their centers. In particular,
Khafrī presented new models for the motions of the Moon, the upper planets,
and Mercury, some more successful than others in meeting the criticisms of
earlier astronomers such as Ibn al‐Haytham.
Khafrī's
model for the lunar motion combined the best features of two previous theories,
namely those of Muʾayyad al‐Dīn
al‐ʿUrḍī and Quṭb
al‐Dīn al‐Shīrāzī. He managed to employ
only spheres that moved uniformly around their own centers, the basic criterion
for physical consistency in Islamic astronomy. Khafrī discussed various
solutions to the irregular lunar motions, including those of Ṭūsī, Shīrāzī, and himself. However, there
are some problems with his model. Because he attempted to make the predictions
of his model coincide as closely as possible with the Ptolemaic lunar model,
especially at the critical points including quadrature, his model replicated
certain errors of Ptolemy's model, including the absurd prediction that the
Moon should appear twice its actual size. Ibn
al‐Shāṭir
had solved this problem, but Khafrī seems to have been unaware of his
work. The fact that Khafrī adheres so closely to Ptolemy's observations
and reproduces one of the major predictive failings of Ptolemaic theory suggests
that Khafrī was more of a theorist than an observational astronomer.
Khafrī
solved the equant problem for the upper planets, Mars, Jupiter, and Saturn,
by following ʿUrḍī's
model with a few adjustments, such as introducing a second deferent as well
as an “epicyclet,” i. e., an epicycle on an epicycle. Again, this model
essentially duplicates all of the Ptolemaic planetary positions while preserving
a physically consistent model.
Khafrī
described four such models for Mercury's motion, one devised by ʿAlī
Qūshjī and three by him. Khafrī
employed all of the techniques and theoretical mechanisms devised in the Islamic
tradition of mathematical astronomy (the Ṭūsī Couple, epicyclets, etc.)
and, in each case, the result was a physically consistent model.
The
work of Khafrī raises the important question of the status of theoretical
models in science. In the Takmila, Khafrī offered several possible
models for the motion of Mercury, each of which was essentially equivalent
in predictive power. This seems to imply that for Khafrī, the model apparently
was simply a tool for predicting planetary positions. If so, then Khafrī
made a significant departure from his predecessors in the entire Graeco–Islamic
tradition. Alternatively, Khafrī may have been attempting to find all
the possible solutions to a scientific problem, from which the scientist must
employ observational criteria to choose the most correct configuration. In
any case, it is not yet known what impact, if any, the work of Khafrī
had or whether it led to any broad reassessment of the aims of science in
Islam.
Two other
works by Khafrī are mentioned in several sources, but have yet to be
studied: Muntahā al‐idrāk fī al‐hayʾa
(The ultimate comprehension of astronomy), written as a refutation or a commentary
on the Nihāyat al‐idrāk fī dirāyat al‐aflāk
(The ultimate understanding of the knowledge of the orbs) of Shīrāzī;
and Ḥall
mā lā yanḥall (Resolution of that not [yet] solved).
Selected References
Al‐Khafrī, Shams al‐Dīn (1994). al‐Takmila
fī sharḥ al‐tadhkira. (This work has been neither edited
nor published in Arabic or English translation. The following manuscripts
were consulted by Saliba (1994): Zāhiriyya Library, Damascus, MSS. 6727
and 6782; India Office Library, London, Arabic MS. 747; and Bibliothèque Nationale,
Paris MS. Arabe 6085.)
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. (Perhaps the most significant study to emerge thus
far in the historiography of astronomy in Islam, in which al‐Ṭūsī's treatise
was pivotal.)
Rosenfeld, B. A. and Ekmeleddin Ihsanoğlu (2003). Mathematicians,
Astronomers, and Other Scholars of Islamic Civilization and Their Works (7th–19th
c.). Istanbul: IRCICA, pp. 313–314.
Saliba, George (1994). A History of Arabic Astronomy: Planetary
Theories during the Golden Age of Islam. New York: New York University
Press. (This is a collection of articles that are useful in that they probe
deeply into several discrete figures and issues from the history of Islamic
astronomy. Saliba provides helpful clarifications of a number of historical
issues, including the nature of the apparent connection between the work of
Islamic astronomers of the “Marāgha School” and the achievement of Nicolaus
Copernicus.)
——— (1994). “A Sixteenth‐century Arabic Critique of Ptolemaic
Astronomy: The Work of Shams al‐Dīn al‐Khafrī.” Journal
for the History of Astronomy 25: 15–38. (Detailed survey of the al‐Takmila
fī sharḥ al‐tadhkira from which the remarks of the present
article were derived.)
——— (1996). “Arabic
Planetary Theories after the Eleventh Century AD.” In Encyclopedia of the
History of Arabic Science, edited by Roshdi Rashed, pp. 58–127. London:
Routledge. (Important survey of the later period of theoretical astronomy
in Islam. Presents many helpful descriptions and diagrams of planetary models,
and traces the often subtle theoretical modifications from one model to the
next.)
——— (1997). “A Redeployment
of Mathematics in a 16th‐Century Arabic Critique of Ptolemaic Astronomy.”
In Perspectives arabes et médiévales
sur la tradition scientifique et philosophique grecque, edited by Ahmad
Hasnawi, pp. 105–122. Paris:
Peeters. (A speculative description of a possibly significant shift in understanding
of the role of mathematical modeling in scientific theory which occurred late
in the history of Islamic astronomy, in the work of Khafrī.)