Al-Farghani

Abu al-Abbas Ahmad ibn Muhammad ibn Kathir al-Farghani — known in medieval Europe by the Latin name Alfraganus — was one of the leading astronomers working under the early Abbasid caliphs. His nisba (the surname marking origin) points to Farghana, in what is now Uzbekistan, though his exact birthplace and dates are not securely documented; he is usually placed around 800-870 CE, and sources describe him variously as Arab or Persian. He flourished mid-ninth century, which is the one date frame the sources treat as firm.

He took part in the program of astronomical observation sponsored by the caliph al-Ma'mun (died 833), associated with measuring a degree of the Earth's meridian to estimate its size. His best-known work, the Kitab fi Jawami ilm al-nujum ("Compendium of the Science of the Stars"), written between roughly 833 and 857, is a clear, largely non-mathematical summary of Ptolemy's astronomy. Translated into Latin and Hebrew, it was read across Europe for centuries and is reported to have influenced figures such as Dante.

Al-Farghani later worked in Egypt, where he is credited with the New Nilometer on Rawda Island near Fustat (old Cairo), completed in 861, used to gauge the Nile's flood. Sources also report that he was given a canal-digging project at al-Ja'fariyya near Samarra under al-Mutawakkil and miscalculated its depth — an episode preserved in the biographical tradition. He is said to have died in Egypt after 861.