| From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 1153-1155 |
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Ṭūsī: Abū Jaʿfar Muḥammad ibn Muḥammad ibn al‐Ḥasan Naṣīr
al‐Dīn al‐Ṭūsī
F. Jamil Ragep
Born Ṭūs (northeast Iran), 17 February
1201
Died Baghdad (Iraq),
25 June 1274
Naṣīr
al‐Dīn al‐Ṭūsī's
major scientific writings in astronomy, in which he worked to reform Ptolemaic
theoretical astronomy, had an enormous influence upon late medieval Islamic
astronomy as well as the work of early‐modern European astronomers,
including Nicholas
Copernicus. Ṭūsī wrote over 150 works, in Arabic and Persian, that dealt
with the ancient mathematical sciences, the Greek philosophical tradition,
and the religious sciences (law [fiqh], dialectical theology [kalām],
and Sufism). He thereby acquired the honorific titles of khwāja
(distinguished scholar and teacher), ustādh al‐bashar (teacher
of mankind), and al‐muʿallim
al‐thālith (the third teacher, the first two being Aristotle
and Fārābī). In addition,
Ṭūsī was the director of the first major astronomical observatory,
which was located in Marāgha (Iran).
Ṭūsī was born into a family
of Imāmī (Twelver) Shīʿa.
His education began first at home; both Ṭūsī's
father and his uncles were scholars who encouraged him to pursue al‐ʿulūm al‐sharʿiyya (the Islamic religious
sciences) as well as the ʿulūm
al‐awāʾil (the rational sciences of the ancients).
He studied the branches of philosophy (ḥikma) and especially mathematics
in Ṭūs, but eventually traveled to Nīshāpūr (after
1213) in order to continue his education in the ancient sciences, medicine,
and philosophy with several noted scholars; among the things he studied were
the works of Ibn Sīnā, who
became an important formative influence. Ṭūsī
then traveled to Iraq where his studies included legal theory; in Mosul (sometime
between 1223 and 1232), one of his teachers was Kamāl al‐Dīn
ibn Yūnus (died: 1242), a legal scholar who was also renowned for his
expertise in astronomy and mathematics.
In the early 1230s, after completing his education, Ṭūsī found patrons at the Ismāʿīlī
courts in eastern Iran; he eventually relocated to Alamūt, the Ismāʿīlī
capital, and witnessed its fall to the Mongols in 1256. Ṭūsī then served under the
Mongols as an advisor to Īlkhānid ruler Hūlāgū Khan,
becoming court astrologer as well as minister of religious endowments (awqāf).
One major outcome was that Ṭūsī oversaw the construction of an astronomical observatory
and its instruments in Marāgha, the Mongol headquarters in Azerbaijan,
and he became its first director. The Marāgha Observatory also comprised
a library and school. It was one of the most ambitious scientific institutions
established up to that time and may be considered the first full‐scale
observatory. It attracted many famous and talented scientists and students
from the Islamic world and even from as far away as China. The observatory
lasted only about 50 years, but its intellectual legacy would have repercussions
from China to Europe for centuries to come. Indeed, it is said that Ulugh
Beg's childhood memory of
visiting the remnants of the Marāgha Observatory as a youth contributed
to his decision to build the Samarqand Observatory. Mughal observatories in
India, such as those built by Jai
Singh in the 18th century, clearly show the influence of these earlier
observatories, and it has been suggested that Tycho
Brahe might have been influenced by them as well. In 1274 Ṭūsī
left Marāgha with a group of his students for Baghdad.
Ṭūsī's writings are both synthetic
and original. His recensions (taḥārīr) of Greek
and early Islamic scientific works, which included his original commentaries,
became the standard in a variety of disciplines. These works included Euclid's
Elements, Ptolemy's
Almagest, and the so called mutawassiṭāt (the �Intermediate Books� that were to be studied
between Euclid's Elements and Ptolemy's Almagest) with treatises
by Euclid, Theodosius,
Hypsicles,
Autolycus,
Aristarchus,
Archimedes,
Menelaus,
Thābit ibn Qurra, and the
Banū Mūsā. In mathematics,
Ṭūsī published a sophisticated �proof� of Euclid's parallels
postulate that was important for the development of non‐Euclidian geometry,
and he treated trigonometry as a discipline independent of astronomy, which
was in many ways similar to what was accomplished later in Europe by Johann
M�ller (Regiomontanus). Other important and influential works include
books on logic, ethics, and a famous commentary on a philosophical work of
Ibn Sīnā.
In astronomy,
Ṭūsī wrote several treatises
on practical astronomy (taqwīm), instruments, astrology, and cosmography/theoretical
astronomy (ʿilm al‐hayʾa). He also compiled a major astronomical handbook (in
Persian) entitled Zīj‐i Īlkhānī for his Mongol
patrons in Marāgha. Virtually all these works were the subject of commentaries
and supercommentaries, and many of his Persian works were translated into
Arabic. They were influential for centuries, some still being used into the
20th century.
Ṭūsī's work in practical astronomy,
as well as his Zīj‐i Īlkhānī,
were not particularly original or innovative. This was not the case with his
work in planetary theory. There he sought to rid the Ptolemaic system of its
inconsistencies, in particular its violations of the fundamental principle
of uniform circular motion in the heavens. Ṭūsī
set forth an astronomical device (now known as the Ṭūsī‐couple)
that consisted of two circles, the smaller of which was internally tangent
to the other that was twice as large. The smaller rotated twice as fast as
the larger and in the opposite direction. Ṭūsī was able to prove that
a given point on the smaller sphere would oscillate along a straight line.
By incorporating this device into his lunar and planetary models, Ṭūsī reproduced Ptolemaic
accuracy while preserving uniform circular motion. A second version of this
couple could produce (approximately) oscillation on a great circle arc, allowing
Ṭūsī to deal with irregularities
in Ptolemy's latitude theories and lunar model.
These models were first found in Ṭūsī's Persian treatise Ḥall‐i mushkilāt‐i
Muʿīniyya (Solution of the difficulties
in the Muʿīniyya), written for his Ismāʿīlī
patrons, and were further developed and incorporated years later in his famous
Arabic work al‐Tadhkira fī ʿilm
al‐hayʾa (Memoir on astronomy), composed during his years with
the Mongols. Ṭūsī's devices are of major significance for several reasons.
First, they produced models that adhered to both physical and mathematical
requirements; the two versions of the Ṭūsī couple, from the perspective
of mathematical astronomy, allowed for a separation of the effect of distance
of the planet from its speed (which had been tied together in the Ptolemaic
models). Ṭūsī was thus able, for example,
to circumvent Ptolemy's reliance on a circular motion to produce a rectilinear,
latitudinal effect. Second, Ṭūsī's new models greatly encouraged and influenced the work
of Islamic astronomers, such as his student Quṭb
al‐Dīn al‐Shīrāzī and Ibn
al‐Shāṭir (14th century) as
well as the work of early‐modern European astronomers such as Copernicus.
The Ṭūsī couple also appears in Sanskrit and Byzantine texts.
Ṭūsī also influenced his
astronomical and cosmological successors with his discussion of the Earth's
motion. Although he remained committed to a geocentric universe, Ṭūsī
criticized Ptolemy's reliance on observational proofs to demonstrate the Earth's
stasis, noting that such proofs were not decisive. Recent research has revealed
a striking similarity between Ṭūsī's arguments and those
of Copernicus.
Ṭūsī was committed to
pursing knowledge in all its forms, and he tried to reconcile the intellectual
traditions of late Greek Antiquity with his Islamic faith. As was the case
with many Islamic scientists, he held that the certitude of the exact mathematical
sciences, especially astronomy and pure mathematics, was a means toward understanding
God's creation.
Selected References
Al‐Ṭūsī, Naṣīr al‐Dīn
(1998). Contemplation and Action (Risālah‐i Sayr wa sulūk),
edited and translated by S. J. Badakhchani. London: I. B. Tauris.
Kusuba, Takanori and David Pingree (2002). Arabic Astronomy
in Sanskrit: Al‐Birjandī on Tadhkira II, Chapter 11 and
Its Sanskrit Translation. Leiden: E. J. Brill. (For the translation of
a part of a commentary on Tūsī's Tadhkira into Sanskrit.)
Ragep, F. Jamil (1987).
�The Two Versions of the Tūsī Couple.� In From Deferent to Equant:
A Volume of Studies in the History of Science in the Ancient and Medieval
Near East in Honor of E. S. Kennedy, edited by David A. King and George
Saliba, pp. 329�356. Annals of the New York Academy of Sciences, Vol. 500.
New York: New York Academy of Sciences.
��� (1993). Naṣīr
al‐Dīn al‐Ṭūsī's Memoir on Astronomy
(al‐Tadhkira fī ʿilm
al‐hayʾa). 2 Vols. New York:
Springer‐Verlag.
��� (2000). �The Persian
Context of the Tūsī Couple.� In Naṣīr al‐Dīn
al‐Ṭūsī: Philosophe et savant du XIIIe si�cle, edited
by N. Pourjavady and �. Vesel, pp. 113�130. Tehran: Institut fran�ais de recherche en
Iran/Presses universitaires d'Iran.
��� (2000). �Al‐Ṭūsī,
Naṣīr al‐Dīn: As scientist.� In Encyclopaedia of
Islam. 2nd ed. Vol. 10, pp. 750�752. Leiden: E. J. Brill.
��� (2001). �Ṭūsī
and Copernicus: The Earth's Motion in Context.� Science in Context
14: 145�163.
��� (2004). �Copernicus
and His Islamic Predecessors: Some Historical Remarks.� Filozofski vestnik
25: 125�142.
Ridawī, M. M. (1976). Aḥwāl wa‐āthār�
Naṣīr al‐Dīn. Tehran: Farhang Iran.
Rosenfeld, B. A. and Ekmeleddin Ihsanoğlu (2003). Mathematicians,
Astronomers, and Other Scholars of Islamic Civilization and Their Works (7th�19th
c.). Istanbul: IRCICA, pp. 211�219.
Sayılı A. (1960). The Observatory in Islam.
Ankara: Turkish Historical Society. (On the Marāgha Observatory, see
pp. 187�223.)