| From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 1129-1130 |
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Courtesy of 
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Thābit ibn Qurra
JoAnn Palmeri
Born near Ḥarrān, upper Mesopotamia, (Turkey),
circa 830
Died Baghdad, (Iraq),
18 February 901
As
a member of the Banū Mūsā
circle of scholars in 9th‐century Baghdad, Thābit ibn Qurra contributed
significantly to the development of astronomy and other sciences through his
translations and commentaries of Greek and Hellenistic works and through his
original treatises. Notable astronomical contributions include a translation
of Ptolemy's
Almagest and treatises on the motion of the Sun and the Moon. More
generally, Thābit's significance lies in the influence of his work on
the development of the exact sciences in Islam.
Thābit
was a member of the Sabian religious sect. His heritage was steeped in traditions
of Hellenistic culture and pagan veneration of the stars. This background,
and in particular, his knowledge of Greek and Arabic, made him an attractive
prospect for inclusion in one particular community of scholars – the Banū
Mūsā and their circle in Baghdad. Thābit seems to have been
asked to join this circle by a family member, the mathematician Muḥammad
ibn Mūsā ibn Shākir, who recognized his talents and potential.
Thābit
remained mainly in Baghdad, becoming a noted translator, physician, and renowned
scholar in a variety of disciplines. As in the case of his mentors and teachers,
Thābit was part of a family tradition of scholarly activity, with son
Sinān ibn Thābit and grandson Ibrāhīm
ibn Sinān Thābit ibn Qurra also making contributions to
medicine and the exact sciences.
Thābit
is credited with dozens of treatises, covering a wide range of fields and
topics. While some were written in his native Syriac, most were composed in
Arabic. Thabit was trilingual, a skill that enabled him to play a key role
in the translation movement of 9th‐century Baghdad. He translated works
from both Syriac and Greek into Arabic, creating Arabic versions of important
Hellenistic and Greek writings. Several of Thābit's Arabic translations
are the only extant versions of important ancient works.
A
large percentage of Thābit's corpus is devoted to mathematics. This includes
translations of Books V–VII of Apollonius's
On Conics and Archimedes'
Lemmata and On Triangles. His work in mathematics also includes
original treatises, with contributions in the many areas of geometry and number
theory. His original contributions include proofs of the Pythagorean theorem,
a proof of Menelaus's theorem, proofs of Euclid's fifth postulate, and work
on composite ratios.
Thābit's
achievements in astronomy are closely linked to his work in mathematics. The
application of his mathematical work (e. g., his theories of
composite ratios) to the examination and development of Ptolemaic astronomy,
as Morelon emphasizes, helped establish a tradition of mathematical astronomy
in Islamic culture. Discussion of Thābit's ideas is found in the work
of later astronomers, including Khāzinī
and Naṣīr
al‐Dīn al‐Ṭūsī.
Thābit's
revision of Ḥunayn ibn Isḥāq's translation of the Almagest
survives in manuscript. In addition, something less than a dozen astronomical
treatises by Thābit have survived, about a fourth of the number he is
credited with composing. Two of these present the basics of Ptolemaic astronomy,
including the structure of the cosmos according to Ptolemy's Planetary
Hypotheses, a work whose Arabic translation Thābit revised. In the
other extant treatises, Thābit addresses the problem of the unequal motion
of the Sun, the motion of the Moon, the determination of crescent visibility,
and the theory of sundials.
Two
treatises traditionally attributed to Thābit are almost certainly not
by him. One of these that survives only in Latin translation is De motu
octave spere (On the motion of the eighth sphere); the misattribution
may be due to the fact that a related treatise was written by his grandson
Ibrāhīm Ibn Sinān. The author of De motu addresses a
type of problem that astronomers in the centuries following Ptolemy have all
had to confront – changes in astronomical parameters as a consequence of elapsed
time. A new model for the precession of the equinoxes is presented in order
to account for such changes. Two time‐related changes that this model
addresses are the increase in the rate of precession and the decrease in the
value of the obliquity of the equinox since the time of the Almagest.
In addition, a theory of oscillation or periodicity of these motions (“trepidation”)
is proposed.
The
other misattributed treatise deals with the solar year. The author of this
work attempts to show why adopting a sidereal year is preferable to accepting
Ptolemy's tropical year as the basic time‐unit for solar motion.
In
addition to his works in mathematical astronomy, Thābit also wrote on
philosophical and cosmological topics, questioning some of the fundamentals
of the Aristotelian cosmos. He rejected Aristotle's
concept of the essence as immobile, a position Rosenfeld and Grigorian suggest
is in keeping with his anti‐Aristotelian stance of allowing the use
of motion in mathematics. Thābit also wrote important treatises related
to Archimedean problems in statics and mechanics.
Thābit's
efforts provided a foundation for continuing work in the investigation and
reformation of Ptolemaic astronomy. His life is illustrative of the fact that
individuals from a wide range of backgrounds and religions contributed to
the flourishing of sciences like astronomy in Islamic culture.
Selected References
Carmody, Francis J. (1960). The Astronomical Works of Thabit
b. Qurra. Berkeley: University of California Press.
Goldstein, Bernard
R. (1964). “On the Theory of Trepidation.” Centaurus 10: 232–247.
Morelon,
Régis (1994). “Ṯābit
b. Qurra and Arab Astronomy in the 9th Century.” Arabic Sciences and Philosophy
4: 111–139.
——— (1996). “Eastern
Arabic Astronomy between the Eighth and the Eleventh Centuries.” In Encyclopedia
of the History of Arabic Science, edited by Roshdi Rashed. Vol. 1, pp.
20–57. London: Routledge.
Neugebauer, Otto (1962). Review of The Astronomical Works
of Thabit b. Qurra, by Francis Carmody. Speculum 37: 99–103.
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. (For a discussion of trepidation and the authorship
of De motu octave spere.)
Rosenfeld, B. A. and A. T. Grigorian (1976). “Thābit ibn
Qurra.” In Dictionary of Scientific Biography, edited by Charles Coulson
Gillispie. Vol. 13, pp. 288–195. New York: Charles Scribner's Sons.
Thābit
ibn Qurra (1987). Oeuvres d'astronomie, edited by Régis Morelon. Paris:
Les Belles Lettres.