Al-Farghani

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. There is some debate about whether the two names for al-Farghani, Muhammad ibn Kath lr and Ahmad ibn Muhammad ibn Kat, mentioned in historical sources refer to two different people, but most historians argue that both names describe just one al-Farghani. ==Works==

is named after him. The most influential work produced by al-Farghani was his textbook Kitāb fī Jawāmiʿ ʿIlm al-Nujūm ( A Compendium of the Science of the Stars) or Elements of astronomy on the celestial motions, written sometime between about 833 and 857. Elements was a descriptive summary of Ptolemy's Almagest that included the findings and revised values of earlier Islamic astronomers. Among the revisions included in the book were corrections to calculations of the circumference of the Earth, the Earth's axial tilt, and the apsides of the Sun and the Moon. Al-Farghani's book was translated into Latin in the 12th century by John of Seville in 1135 and later by Gerard of Cremona prior to 1175. Elements was also translated into Hebrew by Jacob Anatoli sometime from 1231 to 1235. Al-Farghani also wrote several documents about astronomical instruments. His most famous is his treatise on the astrolabe, which is the oldest surviving document that details the theoretical construction and use of the tool. Al-Farghani's treatise on the astrolabe provides the mathematical basis for the construction of the astrolabe, along with tables containing thousands of data points enabling the construction of astrolabes that function at varying lines of longitude. In the 15th century, Christopher Columbus used al-Farghani's estimate for the Earth's circumference as the basis for his voyages to America. However, Columbus mistook al-Farghani's 7091-foot Arabic mile to be a 4856-foot Roman mile. This error caused him to underestimate the Earth's circumference, leading him to sail to North America while he believed that he was taking a shortcut to Asia. ==See also==