Abu al-Abbas Ahmad ibn Muhammad ibn Kathir al-Farghani, also known in the West as Alfraganus, was a Persian Muslim astronomer. He is one of the most famous astronomers of the 9th century. The "Alfraganus" crater on the Moon is named in his honor.
It is accepted that al-Farghani was born in the early 9th century, was alive in 861, and died shortly thereafter.
He pursued his education in Fergana, the cultural center of the time. He then went to Baghdad. Making a name for himself in a short time, al-Farghani established his reputation in the fields of astronomy and mathematics. He carried out important scholarly research and wrote many works during the reigns of the Abbasid caliphs al-Ma'mun, al-Mu'tasim, al-Wathiq, and al-Mutawakkil. Caliph al-Mutawakkil sent al-Farghani, an authority in his field, to Egypt in 861 to direct the construction of the nilometer on the island of Rawda and to supervise the measurement work carried out along the Nile.
Al-Farghani was among the first to criticize an astronomy that was not in accordance with the principles of reason. He did not accept that the celestial bodies were, as Ptolemy and his followers claimed, certain irrational spiritual beings. He proved that they had motions in the form of rational, definite, homocentric, and eccentric circles. He examined the volumes and sizes of the universe and the planets and their distances from one another. His calculations were accepted as unchanging measures in Western astronomy until Copernicus and were used for centuries. Al-Farghani stated that the length of the Sun's radius was 3,250 Arab miles. This was equal to 6,410,000 meters and 3,990 English miles.
Al-Farghani is the scholar who first discovered in the history of science that the Sun too is in motion relative to itself. Until his time, the motion of celestial bodies was known. However, al-Farghani was the scholar who first discovered that the Sun too has an orbit and rotates about its own axis from west to east. Moreover, in his astronomical studies, which continued for 41 years, he calculated the distance between the latitudes (parallels).