Abu'l-Abbas Ahmad al-Farghani

Abu'l-Abbas Ahmad ibn Muhammad ibn Kathir al-Farghani is one of the most prominent and distinguished Arab astronomers.

He was born in Farghana and died in Egypt in 833. His most important work, written in the period between 833 and 857, is "Elements of Astronomy" (Kitab fi al-Harakat al-Samawiya wa Jawami Ilm al-Nujum, a thorough nonmathematical summary of Ptolemaic astronomy. Elements, which was translated into Latin language, exerted great influence upon European astronomy before Regiomontanus. Two treatises on astrolabes by Al-Farghani also survive.

Al Farghani adopted Ptolemy's theory and value of the precession, and reached the conclusion that it doesn't only affected the stars but also the planets. He determined the diameter of the earth to be 6,500 miles.

Ahmed al-Farghani was one of the Pleiad scientists, a member of the House of Wisdom founded by Caliph AL-Ma'mun in the 9th century. The House of Wisdom was also known at that time as the al-Ma'mun Academy. It was first in Mery, then in Baghdad that the scientists whom he invited from Khoresm, Sogdiana, Shash, Farab, Khorosan conducted their scientific. The two observatories were equipped with the most modern equipment at that time. It was there that astronomers from the al-Ma'mun Academy calculated the Earth's circumference, the degree length of the Earth's meridian, investigated the stars, compiled the "zibjes" (tables) and wrote scientific reports.

AI-Farghani was also invited to work along with these scientists. During the period he spent in Egypt, he created the famous "Cairo Nilemeter", a measuring device for the water in the Nile. This tool was an invention that has preserved its scientific value up till now.

Also Al-Farghani contributions in the science of engineering. According to Ibn Tughri Birdi, he supervised the construction of the Great Nilometer at al-Fustat (old Cairo). It was completed in 861, the year in which the Caliph al-Mutawakkil, who ordered the construction, died.

The Fihrist of Ibn al-Nadim, written in 987, ascribes two works to Al-Farghani: (1) "The Book of Chapters, a summary of the Almagest" (Kitab al-Fusul, Ikhtiyar al-Majisti) and (2) "Book on the Construction of Sun-dials" (Kitab 'Amal al-Rukhamat).

'The Elements' was Al- Farghani's major work and most important. Abd al-Aziz al-Qabisi (d. 967) wrote a commentary on it, which is preserved in the Istanbul manuscript, Aya Sofya 4832, fols. 97v-114v.

Two Latin translations of 'The Elements' were written in the 12th century, one by John of Seville in 1135 (revised by Regiomontanus* in the 1460's) and the other by Gerard of Cremona* before 1175, the latter work providing Dante* with the astronomical knowledge used in his 'La Vita Nuova'.

Together with these works, al-Farghani's summary was to a great extent influential in bringing Ptolemy's astronomy to Europe. Jacob Anatoli made a Hebrew translation of al-Farghani's book, and this became the basis for a third Latin version in 1590. Jacob Golius published a new Latin text, along with the Arabic original, in 1669.

Al-Farghani also wrote a book on the construction of sundials, and a treatise on the astrolabe (written around 857) which discussed the mathematical theory of the astrolabe and introduced features (not found on earlier instruments) such as the universal plate of horizons.