Ahmad ibn Muhammad ibn Kathīr al-Farghānī

Abū al-ʿAbbās Aḥmad ibn Muḥammad ibn Kathīr al-Farghānī () also known as Alfraganus in the West (870), was an astronomer in the Abbasid court in Baghdad, and one of the most famous astronomers in the 9th century. Al-Farghani composed several works on astronomy and astronomical equipment that were widely distributed in Arabic and Latin and were influential to many scientists. His best known work, Kitāb fī Jawāmiʿ ʿIlm al-Nujūmi (whose name translates to Elements of astronomy on the celestial motions), was an extensive summary of Ptolemy's Almagest containing revised and more accurate experimental data. Christopher Columbus used Al Farghani's calculations for his voyages to America (but mistakenly interpreted Arabic miles as Roman miles). In addition to making substantial contributions to astronomy, al-Farghani also worked as an engineer, supervising construction projects on rivers in Cairo, Egypt. The lunar crater Alfraganus is named after him.

==Life== Al-Farghani was born sometime in the early 9th century, and his last name suggests that his birthplace was most likely in Quva city, Farghana, Uzbekistan. He has been described as Arab or Persian. He was involved in the calculation of the diameter of the Earth by the measurement of the meridian arc length, together with a team of scientists under the patronage of the ʿAbbāsid caliph al-Ma'mūn in Baghdad. Later he moved to Cairo, where he composed a treatise on the astrolabe around 856. There, he also supervised the construction of the large Nilometer, called the New Nilometer, on the Rawda Island (in Old Cairo) at the behest of the ʿAbbāsid caliph al-Mutawakkil, which was completed in the year 861. This instrument allowed the height of the Nile to be measured in the event of a flood. Also in Cairo, al-Farghani was tasked with building a canal, called al-Ja‘fari, by the two brothers Muhammad and Ahmad ibn Musa, who were themselves ordered by al-Mutawakkil to oversee the construction of the canal. Reports indicate that al-Farghani made a critical mistake in the design of the canal, and had the entrance of the canal dug too deep for water to enter the rest of the canal without unusually high water levels. Al-Mutawakkil was enraged when he heard of the mistake, and so he sent Sanad ibn ‘Ali to assess the culpability of the brothers Muhammad and Ahmad who contracted al-Fraghani to build it. Sanad ibn ‘Ali ultimately reported (deceitfully) to al-Mutawakkil that there was no mistake in the design of the canal created by al-Farghani, which delayed any consequences long enough for the controversy to cease abruptly after the assassination of al-Mutawakkil in 861 that resulted in the canal remaining unfinished. Al-Farghani died in Egypt sometime after 861.