A Zij (Persian: “cord”, “table”) is a collection of astronomical parameters and tables used as the basis for complex astrological calculations. The complex data are either compiled from the generic data of the esoteric Sindhind summa of Brahmagupta, pre-Islamic Babylonian tables or the Handy Tables of Ptolemy. Empirical observations form only a minor contribution, although most zij are adapted to a specific geographical latitude. The majority of lesser zij were produced in Baghdad during the 9th century of the Abbasid caliphate but later adaptions to local conditions also occurred in the western Caliphate at Toledo in particular.
At it’s simplest, the tables of a zij constitute a tractatus on Artes Liberales (astronomy). Some more comprehensive texts on astronomy are also respectfully referred to as zij, even though their tables may be only a small component of the work. Many later Arabic versions contain additional material to aid in various astronomical endeavours, including the equivalent of additional tractati on specific astronomical topics, commentaries on the tables and multiple formulae for astrological inceptions – particularly formulaes identifying the correct times for prayer and determining the direction of Mecca (see Art & Academe, p69-74).
A zij provides a +2 Shape & Material bonus to measuring time and astrology. If used at the correct latitude for which it is written by a character that has read its contents, a zij provides a +2 bonus for calculating astrological inceptions.
Az-Zīj ‛alā Sinī al-‛Arab — by Ibrahim al-Fazari (d. 777) and Muhammad al-Fazari (d. 796/806). A translation of the great Sanskrit Siddhanta by the mystical Brahmagupta but suffering from a much reduced quality due to difficulty with translation and cultural familiarity. Although corrected to the latitude of Baghdad, it remains difficult to use and provides no bonus to calculations in itself. Level 5, Quality 7.
Az-Zīj al-Mahlul min as-Sindhind li-Darajat Daraja — by Yaqūb ibn Tāriq (d. 796). This work is essentially a variant of the first text above, but with some corrections added by one of the initial assistant translators allowing its correct use at the latitude of Baghdad. It has a Level 5, Quality 8.
Zīj al-Sindhind — by al-Khwarizmi (c. 780-850). A simplification of Brahmagupta’s great work, this text is the model for many later zij based on the latitude of Baghdad and referred to by many later astronomical texts of the Arab tradition. Level 3, Quality 11. Later corrected using data from Ptolemy and adapted to the latitude of Cordoba by al-Majriti (Almerithi, circa 1000).
Az-Zij as-Sabi — by Muhammad ibn Jābir al-Harrānī al-Battānī (Albatenius) (853-929). One of the first zij to draw exclusively on Ptolemy’s works rather than the work of Brahmagupta, it is corrected for use at the latitude of Raqqah. Quality 8.
Zij al-Safa’ih (Tables of the disks of the astrolabe) — by Abū Ja’far al-Khāzin (900-971). This work deals primarily with the practical uses of tables and astrolabes. It is considered one of the best works in the field by his successors. It is corrected for use at the latitude of Ray and is primarily a Summa Artes Liberales (astrolabes) rather than Astronomy. Level 3, Quality 12.
Book of Fixed Stars (964) — by Abd al-Rahman al-Sufi (Azophi) (903-986) contains the basic elements of a zij corrected for use at the latitude of Isfahan but is a more comprehensive text on Artes Liberales (astronomy) in general, combining Ptolemaic theory with the anwa or native Arab astronomical tradition. Arabic Summae, Level 6, Quality 7.
Zij al-Kabir al-Hakimi — by Ibn Yunus (c. 950-1009). Constructed with the aid of precise measurements using very large astronomical instruments corrected to the latitude of Cairo, Quality 9.
Az-Zīj al-Jamī wal-Baligh (The comprehensive and mature tables) — by Kushyar ibn Labban (971-1029). For use at the latitude of Baghdad. Quality 7.
Kitab al-Zij (Book of Tables) — Abū Ishāq Ibrāhīm al-Zarqālī (Arzachel) (1028-1087). Corrected the Ptolemaic tables for the latitude of Toledo. Quality 10. Later translated into Latin as the Toledo Tables (reduced Quality of 9), it becomes famous throughout Mythic Europe and a basis for European astronomy.
Az-Zīj As-Sanjarī (Sinjaric Tables) — by al-Khazini (fl. 1115-1130). A set of tables corrected to the latitude of Merv. Quality 7.