| From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 1161-1162 |
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ʿUrḍī: Muʾayyad
(al‐Milla wa‐)
al‐Dīn (Muʾayyad
ibn Barīk [Burayk]) al‐ʿUrḍī (al‐ʿĀmirī al‐Dimashqī)
Petra G. Schmidl
Born probably ʿUrḍ
between Palmyra and Ruṣāfa, (Syria), circa 1200
Died Marāgha,
(Iran), circa 1266
ʿUrḍī was one of the major figures of Islamic astronomy in the 13th
century, and participated in a number of important scientific innovations
and developments. Sometime before 1239, ʿUrḍī moved to Damascus, where he worked as an engineer, a teacher
of geometry. and, possibly, of astronomy as well. In 1252/1253, as he says
in his Risālat al‐Raṣd, he built the socalled
perfect instrument for al‐Malik al‐Manṣūr, Lord of Ḥimṣ. In the 1250s Naṣīr al‐Dīn al‐Ṭūsī asked him to come to
Marāgha in Azerbaijān (now in northwest Iran) to help in the building
of an observatory under the patronage of the Mongol ruler Hülegü. The observatory,
one of the most important ever built in the Islamic world and arguably the
first full‐scale observatory in the modern sense, was founded in 1259,
and ʿUrḍī
arrived in Marāgha in that year (or shortly before). He took part in
building the observatory outside the city and erected special devices and
water wheels to raise the water to the observatory hill; he also participated
in the construction of a mosque and a special building for Hülegü's residence.
At the observatory in Marāgha, ʿUrḍī probably joined in the observations for Ṭūsī's Īlkhānī Zīj and was mentioned
in this treatise. Though a noted astronomer and instrument maker, his participation
in the observatory was limited to its early years, in as much as he constructed
instruments there only before 1261/1262. Several instruments for which ʿUrḍī tells us he prepared models were actually seen by later visitors,
further suggesting that he was not the only instrument maker at Marāgha.
His son Muḥammad, also
a member of the observatory staff, made a copy of his father's Kitāb
al‐Hayʾa and constructed a celestial globe, now preserved in
Dresden, which was used at the observatory. ʿUrḍī,
as well as Ṭūsī, was a member of the
so called School of Marāgha, which also included Quṭb
al‐Dīn al‐Shīrāzi and a number of other
astronomers.
ʿUrḍī's
Risāla fī Kayfiyyat al‐arṣād (or simply Risālat
al‐Raṣd) is a rich and informative
treatise on observational instruments, preserved in a unique manuscript in
Paris. Some of the instruments mentioned in this treatise were well known,
others were invented by ʿUrḍī himself. The treatise mentions the instruments built before
and up to 1261/1262. The introduction describes the determination of the meridian
by means of an “Indian circle.” ʿUrḍī tells us the place and time of the erection of the instruments,
and he also outlines his relationship to Ṭūsī. The following instruments
are mentioned: a mural quadrant, that seems to be used in general for altitude
measurement, as well as for a careful determination of the latitude of Marāgha
and the obliquity of the ecliptic; an armillary sphere for the measurement
of the ecliptic longitude and latitude; a solstitial armilla for the determination
of the obliquity of the ecliptic; an equinoctial armilla for the determination
of the entry of the Sun into the equatorial plane and the path of the Sun
at the equinoxes; a so called dioptrical ruler of Hipparchus
for the measurements of the apparent diameters of the Sun and the Moon and
the observation of eclipses; an azimuth ring for the determination of the
altitude and the azimuth; and several other rulers and instruments, such as
the “perfect instrument” for the measurement of the azimuth. ʿUrḍī
ends with a critique of the parallactical ruler described by Ptolemy.
As for the size of the instruments, ʿUrḍī
remarks that the instruments should be as large as possible to have the required
division of the scales.
ʿUrḍī's Kitāb al‐Hayʾa, written sometime before
ʿUrḍī reached Marāgha in 1259, is a work on theoretical astronomy
that includes a critique of Ptolemy's Almagest and his Planetary
Hypotheses. There exist two versions of ʿUrḍī's
treatise: an earlier one compiled sometime between 1235 and 1245 and a later
version in which he edited whole chapters of his original text to make the
arguments more consistent. In the Kitāb al‐Hayʾa ʿUrḍī
introduces the reader to Ptolemaic astronomy and then explains the difficulties
arising from some of Ptolemy's methods and techniques. He then presents his
own astronomical models as an alternative. For ʿUrḍī,
as well as for other astronomers of the so called School of Marāgha,
the main problem in Ptolemaic astronomy was the lack of consistency between
the mathematical models and the principles of natural philosophy. Examples
occurred in the prosneusis point for the Moon, the deferent in the lunar model,
the equant in the model for the superior planets, the inconsistencies in the
planetary distances, and the inclination and deviation of the spheres of Mercury
and Venus that were meant to account for latitude. In ʿUrḍī's
opinion, these inconsistencies violated the essential consistency between
the theoretical mathematical models and the accepted natural and physical
axioms. ʿUrḍī held to the basic principles of Greek astronomy, especially
the circular and uniform motion of the heavenly bodies, and the Earth as the
unmovable center of the Universe; he also appreciated the validity of the
Ptolemaic planetary observations as quoted in the Almagest. But he
objected to the mathematical models that Ptolemy had devised to describe the
motions of the planets. ʿUrḍī
tried to find astronomical models that would preserve Ptolemy's observations,
and which would also be consistent mathematically as well as physically. To
this end, he devised the ʿUrḍī
lemma, a developed form of the theorem by Apollonius
that transformed eccentric models into epicyclic ones. ʿUrḍī
stated that if we construct two equal lines on the same side of any straight
line so that they make two equal angles with that straight line, be they corresponding
or interior, and if their endpoints are connected, then the line resulting
from connecting them will be parallel to the line upon which they were erected
(Kitāb al‐Hayʾa, p. 220). The new technique of bisecting
the Ptolemaic eccentricity allowed him to preserve Ptolemy's deferent, while
preserving the uniform, circular motions of the celestial orbs that revolve
on their own centers, thus avoiding the apparent contradictions in Ptolemy's
model. ʿUrḍī's
Kitāb al‐Hayʾa was written within a tradition of astronomical
literature that was critical of Ptolemy, but it apparently did not depend
upon the work of Ṭūsī,
who also presented alternative models in several of his works (many of which
were based upon the Ṭūsī couple that transforms
circular motion into linear motion). ʿUrḍī's
work was quoted by Ibn al‐Shāṭir, and influenced Bar
Hebraeus and Quṭb al‐Dīn al‐Shīrāzī.
Furthermore, there are many similarities to Nicholaus
Copernicus's work. ʿUrḍī's
technical alternative to Ptolemy's model for the upper planets is essentially
the same as that in Copernicus's De revolutionibus.
ʿUrḍī also wrote some minor treatises: a commentary on Kharaqī's
astronomical treatise Kitāb al‐Tabṣira
fī ʿilm
al‐hayʾa, that closely follows Kharaqī's wording (extant
in a unique manuscript in Madrid); a supplement to a problem in the Almagest,
probably preserved in Mashhad and Ankara; a short treatise on the determination
of the solar eccentricity, preserved in Ankara and Istanbul; and a Risālat
al‐ʿAmal
fī al‐kura al‐kāmila on the armillary sphere,
mentioned in ʿUrḍī's
Risālat al‐Raṣd
as well as in his Kitāb al‐Hayʾa, which seems no longer
extant. In addition, ʿUrḍī himself, or his son, copied in 1252/1253 the recension of the
Almagest by Ṭūsī, which is preserved in
Cairo.
Both of
ʿUrḍī's
main works, the Risālat al‐Raṣd and the Kitāb
al‐Hayʾa, are characterized by improvement and refinement.
On the one hand, he tried to make precise instruments – some standard, others
of his own invention – that would result in the best observations possible.
The Risālat al‐Raṣd
gives the reader a rare insight into the equipment of a medieval Islamic observatory.
On the other hand, he attempted to make the Ptolemaic astronomy more consistent
by developing new and highly sophisticated planetary theories, some of them
mathematically identical to Copernicus's non‐Ptolemaic models.
Selected References
Drechsler, Adolph (1873). Der Arabische Himmels‐Globus
angefertigt 1279 zu Maragha von Muhammed bin Muwajid Elardhi zugehörig dem
Königl. Mathematisch‐physikalischen Salon zu Dresden. Dresden: Königl.
Hofbuchhandlung von Hermann Burdach. (2nd edition reprinted in Sezgin, Astronomische
Instrumente, Vol. 4, pp. 215–241; (reprinted in Sezgin, School of Marāgha,
Vol. 1, pp. 261–289; and reprinted in Sezgin, Astronomical Instruments,
Vol. 4, pp. 215–241.) (On the celestial globe made by ʿUrḍī's
son.)
Frank, Josef (1929). “Review
of ‘Hugo J. Seemann, Die Instrumente der Sternwarte zu Marâgha nach den
Mitteilungen von al‐ʿUrdî.'” Zeitschrift
für Instrumentenkunde 49: 356–367. (Reprinted in Sezgin, Astronomische
Instrumente, Vol. 6, pp. 130–141; reprinted in Sezgin, School of Marāgha,
Vol. 2, pp. 194–205; and reprinted in Sezgin, Astronomical Instruments,
Vol. 6, pp. 130–141.) (On ʿUrḍī's Risālat
al‐Raṣd.)
Saliba, George (1979). “The First Non‐Ptolemaic Astronomy
at the Maraghah School.” Isis 70: 571–576. (Reprinted in Saliba, History
of Arabic Astronomy, pp. 113–118.)
——— (1979). “The Original
Source of Quṭb al‐Dīn al‐Shīrāzī's Planetary
Model.” Journal for the History of Arabic Science 3: 3–18. (Reprinted
in Saliba, History of Arabic Astronomy, pp. 119–134.)
——— (1985). “The Determination
of the Solar Eccentricity and Apogee According to Muʾayyad al‐Dīn
al‐ʿUrḍī
(d. 1266 A.D.). ” Zeitschrift für die Geschichte der Arabisch–Islamischen
Wissenschaften 2: 47–67. (Reprinted in Saliba, History of Arabic Astronomy,
pp. 187–207.)
——— (1987). “The Height
of the Atmosphere According to Muʾayyad al‐Dīn al‐ʿUrḍī, Quṭb
al‐Dīn al‐Shīrāzī, and Ibn Muʿādh.” 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. 445–465. Annals of the New York Academy of Sciences. Vol.
500. New York: New York Academy of Sciences.
——— (1987). “The Rôle
of Maragha in the Development of Islamic Astronomy: A Scientific Revolution
before the Renaissance.” Revue de synthèse 108: 361–373. (Reprinted
in Saliba, History of Arabic Astronomy, pp. 245–257.)
——— (1989). “A Medieval Arabic Reform of the Ptolemaic Lunar
Model.” Journal for the History of Astronomy 20: 157–164. (Reprinted
in Saliba, History of Arabic Astronomy, pp. 135–142.)
——— (1990): The Astronomical
Work of Muʾayyad al‐Dīn al‐ʿUrḍī
(Kitāb al‐Hayʾa): A Thirteenth Century Reform of Ptolemaic
Astronomy (in Arabic with
English introduction). Bayrūt: Markaz dirāsat al‐wahda al‐ʿarabiyya.
(On ʿUrdī's
Kitāb al‐Hayʾa.)
——— (1991). “The Astronomical
Tradition of Marāgha: A Historical Survey and Prospects for Future Research.”
Arabic Sciences and Astronomy 1: 67–99. (Reprinted in Saliba, History
of Arabic Astronomy, pp. 258–290.)
——— (1994). A History
of Arabic Astronomy: Planetary Theories during the Golden Age of Islam.
New York: New York University Press.
Sayılı, Aydın (1960). The Observatory in Islam.
Ankara: Turkish Historical Society.
Seemann,
Hugo J. (1928). “Die Instrumente der Sternwarte zu Marâgha nach den Mitteilungen
von al ʿUrdî.”
Sitzungsberichte der Physikalisch–medizinischen Sozietät zu Erlangen
60: 15–126. (Reprinted in Sezgin, School of Marāgha. Vol. 2, pp.
81–192 and reprinted in Sezgin, Astronomical Instruments. Vol. 6, pp.
17–129.)
Sezgin, Fuat (ed.) (1990/91). Astronomische Instrumente in
orientalistischenStudien. Vol 4 and 6. Frankfurt: Institute
for the History of Arabic‐Islamic Science.
Sezgin, Fuat (ed.) (1998). The School of Marāgha and
Its Achievements. Vols. 1 and 2. Islamic Mathematics and Astronomy.
Vols. 50 and 51. Frankfurt.
——— (1998). Astronomical
Instruments and Observatories in the Islamic World. Vols. 4 and 6. Islamic
Mathematics and Astronomy. Vols. 88 and 90. Frankfurt.
Tekeli, Sevim (1970). “‘The Article on the Quality of Observations'
by al‐ʿUrdī.” Araztima 8: 157–169.