Al-Farghani

Abu al-Abbas Ahmad ibn Muhammad ibn Kathir al-Farghani was a ninth-century astronomer and engineer, known in Europe by the Latinised name Alfraganus. His year of birth is not known for certain: Uzbek scholars place it around 797–798, and in 1998 the 1200th anniversary of his birth was marked under the auspices of UNESCO. The nisba “al-Farghani” points to the Fergana Valley; Uzbek tradition names Quva as his birthplace. Nothing is known of his family or early years.

His career belongs to the scholarly centres of the Abbasid Caliphate. The eleventh-century Andalusian scholar Said al-Andalusi counts him among the astronomers of the caliph al-Ma’mun (813–833), and many sources link him with the House of Wisdom (Bayt al-Hikma) in Baghdad; Uzbek historians believe he came to Baghdad from Merv with al-Ma’mun’s court in 819. Other scholars date his work to the period when the caliphs resided at Samarra (after 836).

His principal work, “The Compendium of the Science of the Stars” (“Jawami‘ ‘ilm al-nujum”), was written some time between about 833 and 857. In thirty chapters it sets out Ptolemaic astronomy in plain language and without heavy mathematics: the calendars of different peoples, the celestial spheres, the seven climes and their cities, the motions of the Sun, the Moon and the planets, the fixed stars, the distances and sizes of the heavenly bodies, and eclipses. It records the result of the measurement of a degree of the meridian carried out on al-Ma’mun’s orders — 56⅔ Arabic miles.

Al-Farghani wrote one of the oldest surviving treatises on the theory of the astrolabe, setting out the geometrical and computational basis of the instrument together with tables for drawing its circles. He also wrote a commentary on the astronomical tables of al-Khwarizmi; it is lost, but later astronomers, al-Biruni among them, drew on it. The sources also mention his books on the celestial spheres and on sundials.

He worked as an engineer as well. Under the caliph al-Mutawakkil (847–861), the sons of Musa ibn Shakir, Muhammad and Ahmad, entrusted him with digging a canal for the new city of al-Ja‘fariyya near Samarra, but an error in the design meant that too little water entered the canal. In Egypt, on Rawda Island in Cairo, the Nilometer used to measure the level of the Nile was built under his direction (some sources say restored); it was completed in 861 and survives to this day.

The year 861 is the last firm date in al-Farghani’s life. He died in Egypt some time after it (Uzbek sources give 865) and is believed to have been buried in Cairo; his grave has not survived.

In the twelfth century his main work was translated into Latin twice, and in the thirteenth into Hebrew; it became the standard textbook of Ptolemaic astronomy in medieval Europe and was printed at Ferrara in 1493. The lunar crater Alfraganus is named after him. In 1998 a symbolic grave was created for him in Quva, the central park of Fergana bears his name, and in 2007 a monument to him was unveiled beside the Nilometer in Cairo.