From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 455-457

Courtesy of

abash al‐āsib: Abū Jaʿfar Amad ibn ʿAbd Allāh al‐Marwazī

François Charette

Diedprobably Samarra, (Iraq), after 869

abash al‐āsib (literally, “abash the calculator,” with the intended meaning of “mathematical astronomer”) was one of the most original and most influential Muslim astronomers of the formative period of Islamic astronomy. The dates of his birth and death are not known, but according to the bibliographer Ibn al‐Nadīm he died as a centenarian. abash was closely associated with the ʿAbbāsid court; he was active in Baghdad during the reign of Caliph Maʾmūn (813–833). Later, he lived and worked in Samarra, which in 838, became the new administrative capital of the ʿAbbāsid Empire.

abash's biography is yet to be definitively established. The bibliographer Ibn al‐Nadīm (died: 995) mentions abash as a scientist active at the time of Maʾmūn, and Ibn al‐Qifī (died: 1248) adds that he also lived under the reign of al‐Muʿtaim. In his own account of the achievements of the aṣḥāb al‐mumtaan  – the group of scholars involved in the observational project sponsored by Caliph Maʾmūn whose objective was to check the parameters of Ptolemy's Almagestabash does not present himself as one of their protagonists, although he was certainly in close contact with them. The earliest certain date associated with him is given by Ibn Yūnus, who reports an observation conducted by abash in Baghdad in the year 829/830 (i. e., 4 years before the death of Maʾmūn). This is also the date associated with many other mumtaan observations and with the mumtaan star‐table.

Ibn al‐Qifī attributes a zīj (astronomical handbook) to abash. This was compiled when he was a young man in the tradition of the Indian Sindhind, and was based upon the zīj of Khwārizmī. Also ascribed to him is another smaller work, the Zīj al‐Shāh, probably following the same Pahlavi tradition as the eponym work by Fazārī. The composition of those two non‐Ptolemaic zījes must have occurred before 829/830, the year when the mumtaan observational program was inaugurated. But abash is best known to his contemporaries and successors for his authorship of a third zīj, whose content is almost entirely Ptolemaic, and which became known as “the” zīj of abash.

In the introduction to this latter zīj, abash informs his readers that after Maʾmūn's death he took upon himself the task of revising the observational data gathered by the “mumtaan astronomers.” Hence, inspired by Ptolemy's methodology, he conducted his own observations of the Sun and Moon, and also made repeated observations of the remaining planets at specific times. The latest dates associated with abash are recorded in his zīj – 22 April 849, 17 November 860, and 15 September 868. These dates coincide with the reigns of Caliph al‐Mutawakkil (reigned: 847–861) and of his third short‐lived successor al‐Muʿtazz (reigned: 866–869). We can assume that the zīj was finalized after the year 869 and represented abash's ultimate achievement. A further indication of this is the fact that abash uses an obliquity of the ecliptic of 23° 35, a value observed by the Banū Mūsā in Samarra in the year 868/869. He could not have been more than circa 75 years old at that time, which would then imply that he was not born before circa 796. The period 796–894, in fact, seems to be the most reasonable estimate for his life span, and this would make him belong to the same generation as Abū Maʿshar and Kindī. The usual modern references to him as flourishing circa 830 would seem to correspond in actuality to the earliest period of his life.

To summarize, we can divide abash's scientific career into the following four distinct periods:


The early, formative period in Baghdad (circa 815–829), during which he became acquainted with the Indian and Persian astronomical systems through the works of Fazārī and Khwārizmī, and composed two zījes based upon these systems.


The mumtaan period (829–834), during which he presumably had close contacts with the mumtaan group of astronomers in Baghdad and Damascus, and benefited from their new observations and insights. During this crucial period, the superiority of Ptolemy's system became gradually obvious to most specialists. With the resulting consensus in favor of Ptolemaic astronomy and the consequent abandonment of Persian and Indian theories, Islamic astronomy reached a new, stable phase of its development.


The post‐mumtaan period, beginning after the death of Maʾmūn in August 833, and possibly based in Damascus, during which abash pursued his own observational program following the mumtaan tradition.


The Samarra period, covering the last half of his career, during which he finalized his Ptolemaic zīj and composed most of his astronomical works that are now extant.

The Ptolemaic zīj of abash, the only one that is extant, is known under four different names – al‐Zīj al‐Mumtaan and al‐Zīj al‐Maʾmūnī (because it is based on the observational program of the mumtaan group under the sponsorship of Maʾmūn), al‐Zīj al‐Dimashqī (presumably because it was also based on observations conducted by abash in Damascus), and al‐Zīj al‐ʿArabī (because it is based on the Arabic Hijra calendar). There is absolutely no evidence to support the contention that the above appellations might refer to more than a single work. Every reference to “the zīj of abash” encountered in later sources (notably Bīrūnī and Ibn Yūnus) is in accord with the single version of the zīj by this author that is preserved for us. There is an instance where Bīrūnī mentions the zīj of abash in general terms, and later characterizes the same work with the epithet al‐mumtaan. This zīj is the earliest independently compiled Ptolemaic astronomical handbook in the Arabic language that is preserved in its entirety. Undoubtedly, it was also one of the most influential zījes of its generation. Indeed, Bīrūnī, in the early (Khwārizmian) period of his life, utilized it for his own astronomical practice. Although abash follows Ptolemy's models and procedures very closely, he does introduce several new, improved parameters as well as an impressive amount of original computational methods, some of them undoubtedly of Indian origin or inspiration. His zīj also contains a set of auxiliary trigonometric tables, called jadwal al‐taqwīm, which are of singular importance in the history of trigonometry.

Two copies of this zīj are available, one preserved in Istanbul, which preserves fairly well the original text, and a second one in Berlin. The latter is a recension of the original, mixed with materials due to various later astronomers. (A table of concordance with the Istanbul MS is appended to M. Debarnot's survey of the Istanbul MS.) Unfortunately, abash's zīj is yet to be published.

Another work of abash, his Book of Bodies and Distances, is in fact devoted to five different topics of scientific activity conducted under the patronage of Maʾmūn, including an interesting report on the geodetic expedition to determine the radius of the Earth (or equivalently the length of 1° of the meridian). abash also devoted several works to the topic of astronomical instrumentation. An important treatise on the construction of the melon astrolabe, which he probably invented and whose principle is based on an “azimuthal equidistant” mapping, has been published by E. Kennedy et al. (1999). An anonymous treatise on the construction of a highly original but still unexplained universal instrument for timekeeping with the stars, preserved in a unique and incomplete copy, has been published lately, and abash's authorship has been established. D. King recently suggested that this instrument could be a companion to the medieval European universal dial known as navicula de venetiis, which he hypothesizes to be, ultimately, of Islamic origin. abash also composed treatises on the use of the celestial globe, the spherical astrolabe, and the armillary sphere.

abash's graphical procedure (a so–called analemma construction) for determining the direction of Mecca (qibla) is preserved in a letter of Bīrūnī to an Abū Saʿīd (most probably Sijzī), in which the contents of abash's treatise – not extant in its original form but incorporated in his zīj – are summarized. Among several works of his that have not survived are treatises on the construction of the standard planispheric astrolabe, on the prediction of lunar crescent visibility, on the construction of sundials, and on some geometrical problem; also lost are his two critical reports on the observations conducted by the mumtaan group in Baghdad and Damascus.

Selected References

Al‐Hāshimī, ʿAlī ibn Sulaymān. The Book of the Reasons Behind Astronomical Tables (Kitāb fī ʿilal al‐zījāt). (A facsimile reproduction of the unique Arabic text contained in the Bodleian MS Arch. Seld. A.11 with a translation by Fuad I. Haddad and E. S. Kennedy and a commentary by David Pingree and E. S. Kennedy. Delmar, New York: Scholars' Facsimiles and Reprints, 1981.)

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

Ali, Jamil (trans.) (1967). The Determination of the Coordinates of Cities: Al‐Bīrūnī's Tadīd al‐Amākin. Beirut: American University of Beirut.

Berggren, J. L. (1980). “A Comparison of Four Analemmas for Determining the Azimuth of the Qibla.” Journal for the History of Arabic Science 4: 69–80.

——— (1991/1992). “abash's Analemma for Representing Azimuth Circles on the Astrolabe.” Zeitschrift für Geschichte der Arabisch‐Islamischen Wissenschaften 7: 23–30.

Caussin de Perceval, Jean Jacques (1804). “Le livre de la grande table hakémite, observée par … ebn Iounis.” Notices et extraits des manuscrits de la Bibliothèque nationale 7: 16–240.

Charette, François and Petra G. Schmidl (2001). “A Universal Plate for Timekeeping by the Stars by abash al‐āsib: Text, Translation and Preliminary Commentary.” Suhayl 2: 107–159.

Debarnot, Marie‐Thérèse (1987). “The Zīj of abash al‐āsib: A Survey of MS Istanbul Yeni Cami 784/2.” In From Deferent to Equant: A Volume of Studies in the History of Science in the Ancient and Medieval Near East in Honour of E. S. Kennedy, edited by David A. King and George Saliba, pp. 35–69. Annals of the New York Academy of Sciences, vol. 500. New York: National Academy of Sciences.

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.

Irani, R. A. K. (1956). “The ‘Jadwal al‐Taqwīm’ of abash al‐āsib.” Master's thesis, American University of Beirut, Mathematics Department.

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

Kennedy, E. S., et al. Edited by David A. King and Mary Helen Kennedy. Beirut: American University of Beirut, 1983. (Collection of previously published papers, including numerous studies devoted to detailed aspects of Ḥabash's astronomical achievements.)

Kennedy, E. S., P. Kunitzsch, and R. P. Lorch (1999). The Melon‐Shaped Astrolabe in Arabic Astronomy. Texts edited with translation and commentary. Stuttgart: Steiner.

King, David A. (1999). World‐Maps for Finding the Direction and Distance to Mecca. Leiden: E. J. Brill.

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

——— (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.

Langermann, Y. Tzvi (1985). “The Book of Bodies and Distances of abash al‐āsib.” Centaurus 28: 108–128.

Lorch, Richard and Paul Kunitzsch (1985). “abash al‐āsib's Book on the Sphere and Its Use.” Zeitschrift für Geschichte der Arabisch‐Islamischen Wissenschaften 2: 68–98.

Sayılı, Aydın (1955). “The Introductory Section of abash's Astronomical Tables Known as the ‘Damascene’ Zîj.” Ankara Üniversitesi Dil ve Tarih–Coğrafya Fakültesi Dergisi 13: 132–151.

——— (1960). The Observatory in Islam. Ankara: Turkish Historical Society.