Abū al-Fath Abd al-Rahman Mansūr al-Khāzini or simply al-Khāzini (أبوالفتح عبدالرحمن منصور الخازنی (Persian), flourished 1115–1130) was an Iranian^[1][2] astronomer, during the Seljuk Empire.^[3] His astronomical tables written under the patronage of Sultan Sanjar (Zīj al-Sanjarī, 1115) is considered to be one of the major works in mathematical astronomy of the medieval period.^[4]: 107 He provided the positions of fixed stars, and for oblique ascensions and time-equations for the latitude of Marv in which he was based.^[5]: 197 He also wrote extensively on various calendrical systems and on the various manipulations of the calendars.^[4] He was the author of an encyclopedia on scales and water-balances.^[6]

Al-Khazini was an emancipated slave in Marv,^{[5]: 197 [7]} which was then one of the most important cities of Khorasan. He got his name from his master (Abu‘l Husayn ‘Alī ibn Muhammad al-Khāzin al-Marwazī) who was the treasurer of Marv.^[4]: 107 The term khāzin was simply the title of the royal treasurer since the early Islamic period.^[8] His master made provisions so that al-Khazini could obtain a first-class education.^[4] Some believe that al-Khazini was a pupil of Omar Khayyam.^[7] While this is not known, he wrote about Khayyam, in particular, he gave a description of the water-balance invented by him (and improved upon by Al-Isfizari).^[5]: 176 And according to some sources, he collaborated with him on the reformation of the Persian calendar in 1079.^[9]: 199

Al-Khazini was known for being a humble man. He refused thousands of Dinar for his works, saying he did not need much to live on because it was only his cat and himself in his household.^[6] Al-Khazini was one of only about twenty astronomers of the Islamic era who performed original observations.^[6] His works reached Byzantium in the 14th century, in particular, they were studied by George Chrysococces and later by Theodore Meliteniotes.^[4]: 107

Al Khazini seems to have been a high government official under Sanjar ibn Malikshah and the sultan of the Seljuk Empire. He did most of his work in Merv, where they are known for their libraries.^[6] His best-known works are "The Book of the Balance of Wisdom", "Treatise on Astronomical Wisdom", and "The Astronomical Tables for Sanjar".^[6]

"The Book of the Balance of Wisdom" is an encyclopedia of medieval mechanics and hydrostatics composed of eight books with fifty chapters.^[6] It is a study of the hydrostatic balance and the ideas behind statics and hydrostatics, it also covers other unrelated topics.^[6] There are four different manuscripts of "The Book of the Balance of Wisdom" that have survived.^[6] The balance al-Khazini built for Sanjar's treasury was modeled after the balance al-Asfizari, who was a generation older than al-Khazini, built.^[6] Sanjar's treasurer out of fear destroyed al-Asfizari's balance; he was filled with grief when he heard the news.^[6] Al-Khazini called his balance "combined balance" to show honor towards Al-Asfizari.^[6] The meaning of the balance was a "balance of true judgment".^[6] The job of this balance was to help the treasury see what metals were precious and which gems were real or fake.^[6] In "The Book of the Balance of Wisdom" al-Khazini states many different examples from the Koran ways that his balance fits into religion.^[6] When al-Khazini explains the advantages of his balance he says that it "performs the functions of skilled craftsmen", its benefits are theoretical and practical precision.^[6]

The "Treatise on Astronomical Wisdom" is a relatively short work.^[6] It has seven parts and each part is assigned to a different scientific instrument.^[6] The seven instruments include: a triquetrum, a dioptra, a "triangular instrument," a quadrant, devices involving reflection, an astrolabe, and simple tips for viewing things with the naked eye.^[6] The treatise describes each instrument and its uses.^[6]

"The Astronomical Tables for Sanjar" is said to have been composed for Sultan Sanjar, the ruler of Merv and his balance was made for Sanjar's treasury.^[6] The tables in "The Astronomical Tables for Sanjar" are tables of holidays, fasts, etc.^[6] The tables are said to have the latitudes and longitudes of forty-three different stars, along with their magnitudes and (astrological) temperaments.^[6] It is said that al-Khazini's observations for this work were probably done in Merv in various observatories with high quality instruments.^[6]

• Al-Khazini, Book of the Balance of Wisdom (Eng). A Wikimedia pdf of the English translation by Khanikoff and the editors of the Journal of the Oriental Society in 1859 from a single Arabic manuscript which is also reproduced. In 2015, the only available English translation.
• Al-Khazini, Book of the Balance of Wisdom (English). A link to the same at the Internet Archive (see page 1 following).