From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 1249-1250

Courtesy of

Ya ibn Abī Manūr: Abū ʿAlī Ya ibn Abī Manūr al‐Munajjim

Benno van Dalen

FlourishedBaghdad, (Iraq), circa 820

Diednear Aleppo, (Syria), 830

Yayā ibn Abī Manūr was the senior astronomer/astrologer at the court of the ʿAbbāsid caliph Maʾmūn. He is well‐known for his leading role in the earliest systematic astronomical observations in the Islamic world, which were carried out in Baghdad in 828–829, and for the astronomical handbook, al‐Zīj al‐mumtaan, that was written on the basis of these observations.

Yayā was of Persian descent and originally named Bizīst, son of Fīrūzān. Since his father, Abū Manūr Abān, was an astrologer in the service of the second ʿAbbāsid caliph al‐Manūr (754–775), we may assume that Yayā spent his youth in Baghdad. His first known position was as an astrologer for al‐Fal ibn Sahl, vizier of the Caliph Maʾmūn. After al‐Fal was assassinated in February 818, Yayā converted to Islam and adopted his Arabic name. He became a boon companion (Arabic: nadīm) of Maʾmūn, and is known to have made astrological predictions for the caliph on various occasions. He was also associated with the House of Wisdom and is mentioned as a teacher of the Banū Mūsā.

Maʾmūn strongly supported scientific activities, including the translation of Greek and Syriac scientific works into Arabic. In 828 and 829, he ordered astronomical observations to be carried out in the Shammāsiyya quarter of Baghdad with the purpose of verifying the parameters of the astronomical models of Ptolemy as found in his Almagest and Handy Tables. Yayā became one of the most important persons involved in these observations together with Jawharī, Sanad ibn ʿAlī, and Marwarrūdhī.

The observational activities at Baghdad did not last for more than one and a half years. In that period basic observations of the Sun and the Moon were made, but a determination of all planetary parameters was not possible. Some specific values that were found are: 23° 33' for the obliquity of the ecliptic (encountered only in the works of Yayā and incidentally in those of his later contemporary abash al‐āsib); a precession of the equinoxes of 1° in 66 Persian years (which may, however, have been influenced by Sasanian–Iranian measurements); a maximum solar equation of 1° 59'; and a maximum equation of center for Venus of 1° 59'. All four results constituted major improvements upon Ptolemy's outdated or incorrect values.

Yaya's name is associated with an astronomical handbook with tables dedicated to Maʾmūn. This work is known as al‐Zīj al‐Maʾmūnī or, more commonly, al‐Zīj al‐mumtaan, that is the Verified Zīj (Latin Tabulae probatae). A late recension of the Zīj is extant in the manuscript Escorial árabe 927, which contains, besides original material from Yayā, numerous chapters, treatises, and tables of later date. In particular, we find material from the important 10th‐century astronomers Ibn al‐Aʿlam, Būzjānī, and Kūshyār ibn Labbān. Furthermore, there are various tables specifically intended for a geographical latitude of 36°, which corresponds to Mosul rather than to Baghdad. In 2004 the manuscript Leipzig Vollers 821 was recognized to be a recension of the Mumtaan Zīj. In some respects it is similar to the one in the Escorial library, but with fewer later additions. This copy has various insertions originating from Battānī and was apparently used in present‐day southeastern Turkey.

Among the materials in the Escorial manuscript explicitly attributed to Yayā are the tables for the lunar equation and the theory of solar eclipses. The latter is a typical mixture of Indian, Sasanian, and Hellenistic influences. The Ptolemaic table for the solar equation, which is also found in abash's zīj, may not be original, since a table of a more primitive nature is attributed to Yayā in the 14th‐century Ashrafī Zīj. Whereas the planetary equations were directly copied from the Handy Tables, the tables for the latitudes of the Moon and the planets are of a simple sinusoidal type and based on otherwise unknown parameters. A table with longitudes and latitudes of 24 fixed stars is indicated to be for the year 829 and derived from the observations made at Shammāsiyya.

It is not known with certainty whether the original Mumtaan Zīj was a work by Yayā alone or a coproduction of the group of astronomers who were involved in the observations carried out on the order of Maʾmūn and who were referred to as aṣḥāb al‐mumtaan, “authors of the verified (tables).” It is also possible that various of these astronomers wrote their own works with the title Mumtaan Zīj. Similarly, it is unclear what Ibn al‐Nadīm (10th century), the earliest important biographer of Muslim scholars, meant by a “first” and “second” “copy” (Arabic: nuskha) of the work. In any case, the Mumtaan Zīj was very well‐known and frequently quoted. Thābit ibn Qurra (second half of the 9th century) wrote a treatise on the differences between the Mumtaan Zīj and Ptolemy's astronomical tables, which is unfortunately lost.

Very little is known about other works by Yayā. Ibn al‐Nadīm mentions a Maqāla fī ʿamal irtifāʿ suds sāʿa li‐ʿar Madīnat al‐Salām (Treatise on the determination of the altitude of [each] sixth of an hour for the latitude of Baghdad), as well as a Kitābun yatawī ʿalā arād lahu (Book containing his observations) and Rasāʾil ilā jamāʿa fī al‐arād (Letters to colleagues concerning observations). A small astrological work by Yayā entitled Kitāb al‐rujūʿwa‐ʾl‐hubū (Book on retrogradation and descent) is extant in the very late manuscript 173 of Kandilli Observatory in Istanbul. It appears that Yayā was also involved in the measurement of 1° on the meridian that was carried out on the order of Maʾmūn in the Sinjār plain (in northern Iraq). On the other hand, both the book Fī al‐ibāna ʿan al‐falak and a set of measurements of the obliquity made at Marv (mentioned by Bīrūnī in his geographical masterwork Tadīd) have been incorrectly attributed to Yayā by modern authors; in fact, they are associated with the Tahirid Governor of Khurāsān, Manūr ibn ala (circa 870).

Yayā died in the early summer of 830 during the first of Maʾmūn's expeditions against Tarsus in Asia Minor. He was buried in Aleppo, where his tomb could still be seen in the 13th century. Thus the astronomical observations carried out during the years 831 and 832 at the monastery of Dayr Murrān on Mount Qāsiyūn near Damascus and headed by Marwarrūdhī took place after Yayā's death. A number of Yayā's descendants were also boon companions of the ʿAbbāsid caliphs and well‐known scholars. One of his four sons, Abū al‐asan ʿAlī (died: 888), collected a huge library for al‐Fat ibn Khāqān, secretary of caliph al‐Mutawakkil (847–861), where, among others, the famous astrologer Abū Maʿshar is known to have studied. Yayā's grandson Yayā ibn ʿAlī was a famous theorist of music. His great‐great‐grandson Hārūn ibn ʿAlī (died: 987) was an able astronomer and likewise author of a zīj.

Selected References

Al‐Qifī, Jamāl al‐Dīn (1903). Taʾrīkh al‐ḥukamāʾ, edited by J. Lippert. Leipzig: Theodor Weicher.

Dalen, Benno van (1994). “A Table for the True Solar Longitude in the Jāmiʿ Zīj.” In Ad Radices: Festband zum fünfzigjährigen Bestehen des Instituts für Geschichte der Naturwissenschaften der Johann Wolfgang Goethe‐Universität Frankfurt am Main, edited by Anton von Gotstedter, pp. 171–190. Stuttgart: Franz Steiner.

——— (2004). “A Second Manuscript of the Mumtahan Zīj. ” Suhayl 4: 9–44.

Fleischhammer, M. (1993). “Munadjdjim, Banu ‘l‐.” In Encyclopaedia of Islam. 2nd ed. Vol. 7, pp. 558–561. Leiden: E. J. Brill.

Ibn al‐Nadīm (1970). The Fihrist of al‐Nadīm: A Tenth‐Century Survey of Muslim Culture, edited and translated by Bayard Dodge. 2 Vols. New York: Columbia University Press. (This and the biographical dictionaries of Ibn Khallikān and Ibn al‐Qifṭī provide all our information on Yaḥyā's life and relatives.)

Kennedy, E. S. (1956). “A Survey of Islamic Astronomical Tables.” Transactions of the American Philosophical Society, n.s., 46, pt. 2: 121–177, esp. 132 and 145–147. (Reprint, Philadelphia: American Philosophical Society, 1989.)

——— (1977). “The Solar Equation in the Zīj of Yaḥyā b. Abī Manṣūr.” In ΠρIΣMATA (Prismata). Naturwissenschaftsgeschichtliche Studien: Festschrift für Willy Hartner, edited by Y. Maeyama and W. G. Saltzer, pp. 183–186. Wiesbaden: Franz Steiner. (Reprinted in E. S. Kennedy, et al., Studies, pp. 136–139.)

Kennedy, E. S., et al. (1983). Studies in the Islamic Exact Sciences, edited by David A. King and Mary Helen Kennedy. Beirut: American University of Beirut.

Kennedy, E. S. and Nazim, Faris (1970). “The Solar Eclipse Technique of Yaḥyā b. Abī Manṣūr.” Journal for the History of Astronomy 1: 20–38. (Reprinted in E. S. Kennedy, et al., Studies, pp. 185–203.)

King, David A. (2000). “Too Many Cooks … A New Account of the Earliest Muslim Geodetic Measurements.” Suhayl 1: 207–241.

Salam, Hala and E. S. Kennedy (1967). “Solar and Lunar Tables in Early Islamic Astronomy.” Journal of the American Oriental Society 87: 492–497. (Reprinted in E. S. Kennedy, et al., Studies, pp. 108–113.)

Sayılı, Aydın (1960). The Observatory in Islam. Ankara: Turkish Historical Society, esp. pp. 50–87.

Sezgin, Fuat. Geschichte des arabischen Schrifttums. Vol.4, Mathematik (1974): 227; Vol. 6, Astronomie (1978): 136–137; Vol. 7, Astrologie–Meteorologie und Verwandtes (1979): 116. Leiden: E. J. Brill.

——— (ed.) (1986). The Verified Astronomical Tables for the Caliph al‐Maʾmūn. Al‐Zīj al‐Maʾmūnī al‐mumtahan by Yaḥyā ibn Abī Mansūr. Frankfurt am Main: Institute for the History of Arabic–Islamic Science. (Facsimile of the unique manuscript of Yaḥyā's zīj.)

Vernet, Juan (1956). “Las ‘Tabulae Probatae.' ” In Homenaje a Millás‐Vallicrosa. Vol. 2, pp. 501–522. Barcelona: Consejo Superior de Investigaciones Científicas. (Reprinted in Vernet, Estudios sobre historia de la ciencia medieval, pp. 191–212. Barcelona: Universidad de Barcelona, 1979.)

——— (1976). “Yaḥyā ibn Abī Manṣūr.” In Dictionary of Scientific Biography, edited by Charles Coulston Gillispie, Vol. 14, pp. 537–538. New York: Charles Scribner's Sons.

Viladrich, Mercè (1988). “The Planetary Latitude Tables in the Mumtahan Zīj.” Journal for the History of Astronomy 19: 257–268.