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Al-Farghani wrote books on astrolabe (ustarlab), sundials (rukhmat) and astronomical tables.
Al-Farghani wrote a very influential book on astronomy called the Jawami ilm al-najum wal harakat al-samawiyya. It was widely circulated in the West from the early 12th century onwards, and greatly influenced the medieval European astronomers. Al-Farghani was known to the Europeans as Alfraganus.
Abul Abbas Ahmad ibn Muhammad ibn Kathir al-Farghani was a native of Farghana in Central Asia. He lived during the reigns of Caliphs, al-Mamun and al-Mutawakkil. After completing his education with specialisation in astronomy and engineering, he went to Baghdad during the reign of al-Mamun. On account of his proficiency in astronomy, he was included in the team of astronomers set up by al-Mamun to undertake important astronomical observations. He wrote the Jawami ilm al-najum wal harakat al-samawiyya, after the death of al-Mamun (d. 833 AD). Caliph al-Mutawakkil who succeeded al-Mamun sent him to Cairo to supervise the construction of the Great Nilometer (al-miqyas al-kabir), also known as the New Nilometer (al-miqyas al-jadid), which was completed in 247 AH/ 861 AD. The Nilometer was erected to measure the flow of water in the Nile and, thereby, to ascertain the extent of flooding. Al-Farghani was also in charge of the construction of the Jafariya Canal in the new city of al-Jafariya, north of Baghdad. But the result was not satisfactory as enough water did not flow through the length of the canal except when the Dajla/Tigris was high. He died after 247 AH/ 861 AD.
Al-Farghani wrote books on astrolabe (ustarlab), sundials (rukhmat) and astronomical tables, in addition to the Jawami, which is his most important book. It has 30 chapters dealing with various aspects of astronomy. Some of the topics covered are: Egyptian, Greek, Roman, Russian and Arab calendars and their differences; basics of Ptolemaic astronomy; inclination of the ecliptic; the circumference and the diameter of the earth as measured by al-Mamun’s astronomers, ascension of the signs of the zodiac in the direct and oblique spheres (al-aflak al-mustaqim and al-aflak al-maila) and equal and unequal hours; description of the planets, their motions and distances from the earth, movements of the sun, moon and fixed stars, retrograde motions of the wandering planets; magnitudes, eccentricities and epicycles, lunar mansions, comparative sizes of the planets and the earth; parallax and eclipses. Al-Farghani made a comprehensive study of astronomy based on Ptolemy’s Almagest, improved upon Ptolemaic astronomy, presented a few of his own ideas and employed an easy and organised pattern to present the complex subject of astronomy which made his book popular for a long time.
Some of the ideas presented by al-Farghani are: inclination of the ecliptic - 23°33' for 214 AH/ 829 AD at Baghdad against Ptolemy’s 23°51'; circumference of the earth - 20,400 miles and diameter of the earth - approximately 6,500 miles; the slow eastward motion of the sphere of the fixed stars about the poles of the ecliptic through one degree every 100 years, is common to spheres of the sun, moon and the five planets.
The Jawami was translated into Latin in 1135 AD, 1175 and 1590, and into Hebrew before 1590. It was printed in Europe in 1493, 1537, 1546, 1556, 1564, 1590, 1618, 1669, 1910, and 1943.
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