Al-Urdi (full name: Moayad Al-Din Al-Urdi Al-Amiri Al-Dimashqi)
() (d. 1266) was a medieval
Syrian
Syrians () are the majority inhabitants of Syria, indigenous to the Levant, most of whom have Arabic, especially its Levantine and Mesopotamian dialects, as a mother tongue. The cultural and linguistic heritage of the Syrian people is a blend ...
Arab astronomer and
geometer.
Born circa 1200, presumably (from the
nisba ''al‐ʿUrḍī'') in the village of ''ʿUrḍ'' in the
Syrian desert
The Syrian Desert ( ''Bādiyat Ash-Shām''), also known as the North Arabian Desert, the Jordanian steppe, or the Badiya, is a region of desert, semi-desert, and steppe, covering about of West Asia, including parts of northern Saudi Arabia, ea ...
between
Palmyra
Palmyra ( ; Palmyrene dialect, Palmyrene: (), romanized: ''Tadmor''; ) is an ancient city in central Syria. It is located in the eastern part of the Levant, and archaeological finds date back to the Neolithic period, and documents first menti ...
and
Resafa
Resafa (), sometimes spelled Rusafa, and known in the Byzantine era as Sergiopolis ( or , ) and briefly as Anastasiopolis (, ), was a city located in the Roman province of Euphratensis, in modern-day Syria. It is an archaeological site situated so ...
, he moved to
Damascus
Damascus ( , ; ) is the capital and List of largest cities in the Levant region by population, largest city of Syria. It is the oldest capital in the world and, according to some, the fourth Holiest sites in Islam, holiest city in Islam. Kno ...
at some point before 1239, where he worked as an engineer and teacher of geometry, and built instruments for
al-Malik al-Mansur of
Hims. In 1259 he moved to
Maragha
Maragheh () is a city in the Central District of Maragheh County, East Azerbaijan province, Iran, serving as capital of both the county and the district. Maragheh is on the bank of the river Sufi Chay. It is from Tabriz, the largest city ...
in northwestern Iran, after being asked by
Nasir al-Din al-Tusi
Muḥammad ibn Muḥammad ibn al-Ḥasan al-Ṭūsī (1201 – 1274), also known as Naṣīr al-Dīn al-Ṭūsī (; ) or simply as (al-)Tusi, was a Persians, Persian polymath, architect, Early Islamic philosophy, philosopher, Islamic medicine, phy ...
to help establish the
Maragha observatory under the patronage of
Hulagu
Hulegu Khan, also known as Hülegü or Hulagu; ; ; ; ( 8 February 1265), was a Mongol ruler who conquered much of Western Asia. As a son of Tolui and the Keraite princess Sorghaghtani Beki, he was a grandson of Genghis Khan and brother of Ar ...
.
PDF version
Al-Urdi's most notable works are ''Risālat al-Raṣd'', a treatise on observational instruments, and ''Kitāb al-Hayʾa'' (كتاب الهيئة), a work on theoretical astronomy. His influence can be seen on
Bar Hebraeus and
Qutb al-Din al-Shirazi
Qotb al-Din Mahmoud b. Zia al-Din Mas'ud b. Mosleh Shirazi (; 1236–1311) was a 13th-century Persian polymath and poet who made contributions to astronomy, mathematics, medicine, physics, music theory, philosophy and Sufism.Sayyed ʿAbd-Allā ...
, in addition to being quoted by
Ibn al-Shatir
ʿAbu al-Ḥasan Alāʾ al‐Dīn bin Alī bin Ibrāhīm bin Muhammad bin al-Matam al-Ansari, known as Ibn al-Shatir or Ibn ash-Shatir (; 1304–1375) was an Arab astronomer, mathematician and engineer. He worked as '' muwaqqit'' (موقت, timek ...
.
Al-Urdi contributed to the construction of the observatory outside of the city, constructing special devices and water wheels in order to supply the observatory, which was built on a hill, with drinking water. He also constructed some of the instruments used in the observatory, in the year 1261/2.
Al-Urdi's son, who also worked in the observatory, made a copy of his father's ''Kitāb al‐Hayʾa'' and also constructed a
celestial globe
Celestial globes show the apparent positions of the stars in the sky. They omit the Sun, Moon, and planets because the positions of these bodies vary relative to those of the stars, but the ecliptic, along which the Sun moves, is indicated.
...
in 1279.
Al-Urdi is a member of the group of Islamic astronomers of the 13th and 14th centuries who were active in the criticism of the astronomical model presented in
Ptolemy
Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...
's ''
Almagest
The ''Almagest'' ( ) is a 2nd-century Greek mathematics, mathematical and Greek astronomy, astronomical treatise on the apparent motions of the stars and planetary paths, written by Ptolemy, Claudius Ptolemy ( ) in Koine Greek. One of the most i ...
''. Saliba (1979) identified
Bodleian ms. Marsh
In ecology, a marsh is a wetland that is dominated by herbaceous plants rather than by woody plants.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p More in genera ...
621 as a copy of Al-Urdi's ''Kitāb al-Hayʾa'', based on which he argued that Al-Urdi's contributions predated
Al-Tusi.
Otto E. Neugebauer
Otto Eduard Neugebauer (May 26, 1899 – February 19, 1990) was an Austrian-American mathematician and historian of science who became known for his research on the history of astronomy and the other exact sciences as they were practiced in a ...
in 1957 argued that the works of this group of astronomers, perhaps via
Ibn al-Shatir
ʿAbu al-Ḥasan Alāʾ al‐Dīn bin Alī bin Ibrāhīm bin Muhammad bin al-Matam al-Ansari, known as Ibn al-Shatir or Ibn ash-Shatir (; 1304–1375) was an Arab astronomer, mathematician and engineer. He worked as '' muwaqqit'' (موقت, timek ...
, must have been received in 15th-century Europe and ultimately influenced the works of
Copernicus
Nicolaus Copernicus (19 February 1473 – 24 May 1543) was a Renaissance polymath who formulated a mathematical model, model of Celestial spheres#Renaissance, the universe that placed heliocentrism, the Sun rather than Earth at its cen ...
.
This concerns the "Urdi lemma" in particular, an extension of
Apollonius' theorem
In geometry, Apollonius's theorem is a theorem relating the length of a median of a triangle to the lengths of its sides. It states that the sum of the squares of any two sides of any triangle equals twice the square on half the third side, toge ...
that allowed an
equant
Equant (or punctum aequans) is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of the planets. The equant is used to explain the observed speed change in different stages of the plane ...
in an astronomic model to be replaced with an equivalent
epicycle
In the Hipparchian, Ptolemaic, and Copernican systems of astronomy, the epicycle (, meaning "circle moving on another circle") was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, ...
that moved around a deferent centered at half the distance to the equant point.
See also
*
Zij-i Ilkhani
''Zīj-i Īlkhānī'' () or ''Ilkhanic Tables'' (literal translation: "The Ilkhan Stars", after ilkhan Hulagu, who was the patron of the author at that time) is a ''Zij'' book with Ephemeris, astronomical tables of planetary movements. It was com ...
References
Further reading
*
George Saliba (1979). "The First Non-Ptolemaic Astronomy at the Maraghah School", ''
Isis
Isis was a major goddess in ancient Egyptian religion whose worship spread throughout the Greco-Roman world. Isis was first mentioned in the Old Kingdom () as one of the main characters of the Osiris myth, in which she resurrects her sla ...
'' 70 (4), p. 571-576.
*
George Saliba (1990). ''The Astronomical Work of Mu'ayyad al-Din al-'Urdi (d. 1266): A Thirteenth Century Reform of Ptolemaic Astronomy'', Markaz dirasat al-Wahda al-'Arabiya, Beirut.
{{DEFAULTSORT:Urdi
Year of birth unknown
1266 deaths
13th-century astronomers
Medieval Syrian astronomers
Medieval Syrian mathematicians
13th-century Syrian people