Yaḥyā ibn
Abī Manṣūr: Abū ʿAlī Yaḥyā ibn Abī Manṣūr al‐Munajjim
Benno van Dalen
Flourished Baghdad, (Iraq),
circa 820
Died near Aleppo,
(Syria), 830
Yaḥyā
ibn Abī Manṣūr 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‐mumtaḥan,
that was written on the basis of these observations.
Yaḥyā
was of Persian descent and originally named Bizīst, son of Fīrūzān.
Since his father, Abū Manṣūr Abān, was an astrologer in the service of the
second ʿAbbāsid
caliph al‐Manṣūr
(754–775), we may assume that Yaḥyā spent his youth in Baghdad. His first known position
was as an astrologer for al‐Faḍl ibn Sahl, vizier of the Caliph
Maʾmūn. After al‐Faḍl
was assassinated in February 818, Yaḥyā 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. Yaḥyā
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
Yaḥyā and incidentally in
those of his later contemporary Ḥabash
al‐Ḥāsib); 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major improvements upon Ptolemy's outdated or incorrect values.
Yaḥya'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‐mumtaḥan, 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 Yaḥyā,
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 Mumtaḥan
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 Yaḥyā 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 Ḥabash's zīj, may not be original, since a table of a more
primitive nature is attributed to Yaḥyā
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 Mumtaḥan Zīj was a work by
Yaḥyā 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‐mumtaḥan,
“authors of the verified (tables).” It is also possible that various of
these astronomers wrote their own works with the title Mumtaḥan 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 Mumtaḥan 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 Mumtaḥan Zīj and Ptolemy's
astronomical tables, which is unfortunately lost.
Very little is known about other works by Yaḥyā. Ibn al‐Nadīm mentions a Maqāla
fī ʿamal
irtifāʿ suds sāʿa li‐ʿarḍ
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 yaḥtawī ʿalā
arṣād lahu
(Book containing his observations) and Rasāʾil ilā jamāʿa fī al‐arṣād (Letters to colleagues concerning
observations). A small astrological work by Yaḥyā entitled Kitāb
al‐rujūʿwa‐ʾl‐hubūṭ (Book on retrogradation
and descent) is extant in the very late manuscript 173 of Kandilli Observatory
in Istanbul. It appears that Yaḥyā
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 Taḥdīd) have been incorrectly attributed to Yaḥyā
by modern authors; in fact, they are associated with the Tahirid Governor
of Khurāsān, Manṣūr ibn Ṭalḥa
(circa 870).
Yaḥyā
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 Yaḥyā's death. A number of
Yaḥyā's descendants
were also boon companions of the ʿAbbāsid
caliphs and well‐known scholars. One of his four sons, Abū al‐Ḥasan ʿAlī (died: 888), collected a huge library for al‐Fatḥ ibn Khāqān, secretary of caliph al‐Mutawakkil
(847–861), where, among others, the famous astrologer Abū
Maʿshar is known to have studied.
Yaḥyā's grandson
Yaḥyā 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‐Qifṭī,
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.