Zij

Zīj (Persian: زيج) is the generic name applied to Islamic astronomical books that tabulate parameters used for astronomical calculations of the positions of the Sun, Moon, stars, and planets. The name is derived from the Middle Persian term zih or zīg, meaning cord. The term is believed to refer to the arrangement of threads in weaving, which was transferred to the arrangement of rows and columns in tabulated data. In addition to the term zīj, some were called by the name qānūn, derived from the equivalent Greek word, κανών.

Some of the early zījes tabulated data from Indian planetary theory (known as the Sindhind) and from pre-Islamic Persian models, but most zījes presented data based on the Ptolemaic model. A small number of the zījes adopted their computations reflecting original observations but most only adopted their tables to reflect the use of a different calendar or geographic longitude as the basis for computations. Since most zījes generally followed earlier theory, their principle contributions reflected improved trigonometrical, computational and observational techniques.

The content of zījes were initially based on that of the Handy Tables (known in Arabic as al-Qānūn) by Egyptian astronomer Ptolemy, the Zij-i Shah compiled in Sassanid Persia, and the Indian Siddhantas by Aryabhata and Brahmagupta. Arabic zijes, however, were more extensive, and typically included materials on chronology, geographical latitudes and longitudes, star tables, trigonometrical functions, functions in spherical astronomy, the equation of time, planetary motions, computation of eclipses, tables for first visibility of the lunar crescent, astronomical and/or astrological computations, and instructions for astronomical calculations using epicyclic geocentric models. Some zījes go beyond this traditional content to explain or prove the theory or report the observations from which the tables were computed.

Over 200 different zījes have been identified that were produced by Islamic astronomers during the period from the eighth to the fifteenth centuries. The greatest centers of production of zījes were Baghdad under the Abassid caliphs in the 9th century, the Maragheh observatory in the 13th century, the Samarkand observatory in the 15th century, and the Istanbul observatory of Taqi al-Din in the 16th century. Nearly 100 more zijes were also produced in India between the 16th and 18th centuries.

List of zijes

• Az-Zīj ‛alā Sinī al-‛Arab — by Ibrahim al-Fazari (d. 777) and Muhammad al-Fazari (d. 796/806)
• Az-Zīj al-Mahlul min as-Sindhind li-Darajat Daraja — by Yaqūb ibn Tāriq (d. 796)
• Zīj al-Sindhind — by al-Khwarizmi (c. 780-850)
• Az-Zij as-Sabi — by Muhammad ibn Jābir al-Harrānī al-Battānī (Albatenius) (853-929)
• Zij al-Safa'ih (Tables of the disks of the astrolabe) — by Abū Ja'far al-Khāzin (900-971)
• Book of Fixed Stars (964) — by Abd al-Rahman al-Sufi (Azophi) (903-986)
• Zij al-Kabir al-Hakimi — by Ibn Yunus (c. 950-1009)
• Az-Zīj al-Jamī wal-Baligh (The Comprehensive and Mature Tables) — by Kushyar ibn Labban (971-1029)
• Almanac of Azarqueil (1088) — by Abū Ishāq Ibrāhīm al-Zarqālī (Azarqueil) (1028–1087)
• Tables of Toledo — based on Abū Ishāq Ibrāhīm al-Zarqālī (Azarqueil) (1028–1087)
• Az-Zīj As-Sanjarī (Sinjaric Tables) — by al-Khazini (fl. 1115-1130)
• Zij-i Ilkhani — by Nasīr al-Dīn al-Tūsī (1201–1274)
• Khaqani Zij — by Jamshīd al-Kāshī (1380–1429)
• Zij-i-Sultani (1437) — by Ulugh Beg
• Unbored Pearl (1579–1580) — by Taqi al-Din

References

• E. S. Kennedy. A Survey of Islamic Astronomical Tables, (Transactions of the American Philosophical Society, New Series, 46, 2.) Philadelphia, 1956. (A revised version in preparation by Benno van Dalen will include over 200 zijes).