| From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 569-570 |
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Ibn al‐Shāṭir: ʿAlāʾ al‐Dīn ʿAlī ibn Ibrāhīm
David A. King
Born Damascus (Syria),
circa 1305
Died Damascus (Syria),
circa 1375
Ibn
al‐Shāṭir
was the most distinguished Muslim astronomer of the 14th century. Although
he was head muwaqqit at the Umayyad mosque in Damascus, responsible
for the regulation of the astronomically defined times of prayer, his works
on astronomical timekeeping are considerably less significant than those of
his colleague Khalīlī. On the
other hand, Ibn al‐Shāṭir, continuing the tradition
of Ibn al‐Sarrāj, made substantial advances in the design of astronomical
instruments. Nevertheless, his most significant contribution to astronomy
was his planetary theory.
In
his planetary models, Ibn al‐Shāṭir incorporated various ingenious
modifications of those of Ptolemy.
Also, with the reservation that they are geocentric, his models are the same
as a number used by Nicolaus
Copernicus. Ibn al‐Shāṭir's planetary theory was investigated
for the first time in the 1950s, and the discovery that his models were mathematically
identical to those of Copernicus raised the very interesting question of a
possible transmission of his planetary theory to Europe. This question has
since been the subject of a number of investigations, but research on the
astronomy of Ibn al‐Shāṭir
and of his sources, let alone on the later influence of his planetary theory
in the Islamic world or Europe, is still at a preliminary stage. It is known,
however, that Copernicus' Mercury model is that of Ibn al‐Shāṭir
and that Copernicus did not properly understand it.
Ibn
al‐Shāṭir
appears to have begun his work on planetary astronomy by preparing a zīj,
an astronomical handbook with tables. This work, which was based on strictly
Ptolemaic planetary theory, has not survived. In a later treatise entitled
Taʿlīq al‐arṣād
(Comments on observations), he described the observations and procedures with
which he had constructed his new planetary models and derived new parameters.
No copy of this treatise is known to exist in the manuscript sources. Later,
in Nihāyat al‐suʾl fī taṣḥīḥ
al‐uṣūl
(A final inquiry concerning the rectification of planetary theory), Ibn al‐Shāṭir presented the reasoning behind
his new planetary models. This work has survived. Finally, Ibn al‐Shāṭir's al‐Zīj al‐jadīd
(The new astronomical handbook), extant in several manuscript copies, contains
a new set of planetary tables based on his new theory and parameters.
Several
works by the scholars of the mid‐13th century observatory at Marāgha
are mentioned in Ibn al‐Shāṭir's introduction to this treatise,
and it is clear that these were the main sources of inspiration for his own
non‐Ptolemaic planetary models.
The
essence of Ibn al‐Shāṭir's planetary theory is the
apparent removal of the eccentric deferent and equant of the Ptolemaic models,
with secondary epicycles used instead. The motivation for this was at first
sight aesthetic rather than scientific, but his major work on observations
is not available to us, so this is not really verifiable. In any case, the
ultimate object was to produce a planetary theory composed of uniform motions
in circular orbits rather than to improve the bases of practical astronomy.
In the case of the Sun, no apparent advantage was gained by the additional
epicycle. In the case of the Moon, the new configuration to some extent corrected
the major defect of the Ptolemaic lunar theory, since it considerably reduced
the variation of the lunar distance. In the case of the planets, the relative
sizes of the primary and secondary epicycles were chosen so that the models
were mathematically equivalent to those of Ptolemy.
Ibn
al‐Shāṭir
also compiled a set of tables displaying the values of certain spherical astronomical
functions relating to the times of prayer. The latitude used for these tables
was 34°, corresponding to an unspecified locality just north of Damascus.
These tables display such functions as the duration of morning and evening
twilight and the time of the afternoon prayer, as well as standard spherical
astronomical functions.
Ibn
al‐Shāṭir
designed and constructed a magnificent horizontal sundial that was erected
on the northern minaret of the Umayyad Mosque in Damascus. The instrument
now on the minaret is an exact copy made in the late 19th century. Fragments
of the original instrument are preserved in the garden of the National Museum,
Damascus. Ibn al‐Shāṭir's sundial, made of marble
and a monumental 2 m × 1 m in size, bore a complex system of curves engraved
on the marble that enabled the muwaqqit to read the time of day in
equinoctial hours since sunrise or before sunset or with respect to either
midday or the time of the afternoon prayer, as well as with respect to daybreak
and nightfall. The gnomon is aligned toward the celestial pole, a development
in gnomonics usually ascribed to European astronomers.
A much
smaller sundial forms part of a compendium made by Ibn al‐Shāṭir,
now preserved in Aleppo. It is contained in a box called ṣandūq al‐yawāqīt (jewel box), measuring 12 cm × 12
cm × 3 cm. It could be used to find the times (al‐mawāqīt)
of the midday and afternoon prayers, as well as to establish the local meridian
and the direction of Mecca.
Ibn
al‐Shāṭir
wrote on the ordinary planispheric astrolabe and designed an astrolabe that
he called al‐āla al‐jāmiʿa
(the universal instrument). He also wrote on the two most commonly used quadrants,
the astrolabic and the trigonometric varieties. Two special quadrants that
he designed were modifications of the simpler and ultimately more useful sine
quadrant. One astrolabe and one universal instrument actually made by Ibn
al‐Shāṭir
survive.
A
contemporary historian reported that he visited Ibn al‐Shāṭir
in 1343 and inspected an “astrolabe” that the latter had constructed. His
account is difficult to understand, but it appears that the instrument was
shaped like an arch, measured three‐quarters of a cubit in length, and
was fixed perpendicular to a wall. Part of the instrument rotated once in
24 hours and somehow displayed both the equinoctial and the seasonal hours.
The driving mechanism was not visible and probably was built into the wall.
Apart from this obscure reference we have no contemporary record of any continuation
of the sophisticated tradition of mechanical devices that flourished in Syria
some 200 years before his time.
Later astronomers
in Damascus and Cairo, none of whom appear to have been particularly interested
in Ibn al‐Shāṭir's non‐Ptolemaic models,
prepared commentaries on, and new versions of, his zīj. In its
original form and in various recensions, this work was used in both cities
for several centuries. His principal treatises on instruments remained popular
for several centuries in Syria, Egypt, and Turkey, the three centers of astronomical
timekeeping in the Islamic world. Thus Ibn al‐Shāṭir's
influence in later Islamic astronomy was widespread but, as far as we can
tell, unfruitful. On the other hand, the reappearance of his planetary models
in the writings of Copernicus, especially his misunderstood Mercury model,
is clear evidence of the transmission of some details of these models beyond
the frontiers of Islam.
Selected References
Hartner, Willy
(1971). “Trepidation and Planetary Theories: Common Features in Late Islamic
and Early Renaissance Astronomy.” In Oriente e occidente nel medioevo, pp. 609–629. Fondazione Alessandro
Volta, Atti dei convegni, 13. Rome: Accademia Nazionale dei Lincei.
Ibn
al‐Shāṭir. al‐Zīj al‐jadīd.
Oxford, Bodleian Library MS A30.
Janin, Louis
(1972). “Le Cadran Solaire de la Mosquée Umayyade à Damas.” Centaurus 16:
285–298. (Reprinted in Kennedy and Ghanem,
pp. 107–121.)
Janin,
Louis and D. A. King (1977). “Ibn al‐Shāṭir's
Ṣandūq al‐yawāqīt:
An Astronomical ‘Compendium.'” Journal for the History of Arabic
Science 1: 187–256. (Reprinted in King, Islamic Astronomical Instruments,
XII. London: Variorum Reprints, 1987; Reprint, Aldershot:
Variorum, 1995.)
Kennedy, E. S. (1956). “A Survey
of Islamic Astronomical Tables.” Transactions of the American Philosophical
Society, n.s., 46, pt. 2: 121–177.
Kennedy, E. S. and
Imad Ghanem (eds.) (1976).
The Life and Work of Ibn al‐Shāṭir, an Arab Astronomer of the Fourteenth Century.
Aleppo: Institute for History of Arabic Science.
——— et al. (1983). Studies
in the Islamic Exact Sciences, edited by David A. King and Mary Helen
Kennedy. Beirut: American University of Beirut. (Contains
reprints of all of the early studies of Ibn al‐Shāṭir's planetary theory.)
King, David A. (1975).“Ibn al‐Shāṭir.”
In Dictionary of Scientific Biography, edited by Charles Coulston Gillispie. Vol. 12, pp.
357–364. New York: Charles Scribner's Sons.
——— (1983). “The Astronomy of the
Mamluks.” Isis 74: 531–555. (Reprinted in King, Islamic
Mathematical Astronomy, III. London: Variorum
Reprints, 1986; 2nd rev. ed., Aldershot: Variorum, 1993.)
——— (1993).
“L'astronomie en Syrie à l'époque islamique.” In Syrie, mémoire et civilization
[exhibition catalogue] edited by Sophie Cluzan, Eric Delpont, and Jeanne Mouliérac,
pp. 391–392, 435, 439. Paris: Institut du monde arabe and Flammarion.
——— (2004). In Synchrony with
the Heavens: Studies in Astronomical Timekeeping and Instrumentation in Medieval
Islamic Civilization. Vol. 1, The Call
of the Muezzin (Studies I–IX), Leiden: E. J.
Brill, II–9.3.
——— (2005). In Synchrony with
the Heavens: Studies in Astronomical Timekeeping and Instrumentation in Medieval
Islamic Civilization. Vol 2, Instruments
of Mass Calculation, XIVb–4 and 8.
Saliba, George
(1987). “Theory and Observation in Islamic Astronomy: The Work of Ibn al‐ Shāṭir
of Damascus.” Journal for the History of Astronomy 18: 35–43. (Reprinted
in Saliba, A History of Arabic Astronomy: Planetary
Theories during the Golden Age of Islam. New York: New York University
Press, 1994, pp. 233–241.)
Schmalzl, Peter
(1929). Zur Geschichte des Quadranten bei den Arabern. Munich: Salesianische
Offizin. (Partly reprinted in
Kennedy and Ghanem, pp. 27–35.)