Astronomy appears to have been always a favourite science with the Arabs from the earliest times. In A.D. 772 there appeared at the court of the Khalif Mansur (A.D. 754-775), Muhammad bin Ibrahim bin Habib al Fezari, the astronomer, who brought with him the tables called Sind Hind, in which the motions of the stars were calculated according to degrees. They contained other observations on solar eclipses and the rising of the signs of the zodiac, extracted by him from the tables ascribed to the Indian king, Figar. The Khalif Mansur ordered this book to be translated into Arabic to serve as a guide for Arab astronomers. And these tables remained in use till the time of the Khalif Mamun (A.D. 813-833), when other revised ones bearing his name came into vogue. These, again, were abridged by Abul Ma'shar (Albumasar, died A.D. 885-886), called the prince of Arabian astrologers, who, however, deviated from them, and inclined towards the system of the Persians and of Ptolemy. This second revision was more favourably received by the Arab astronomers than the first, and the Sind Hind was superseded by the Almagest of Ptolemy. Better astronomical instruments also came into use, though previously the Al-Fezari above mentioned had been the first in Islam who constructed astrolabes of various kinds, and had written several astronomical treatises. Mention might be made of about forty mathematicians and astronomers who wrote books on these subjects. The best of them, such as Al-Farghani (Alfraganius) and others, lived at the court of Mamun, who built an astronomical observatory in Baghdad and another near Damascus, on Mount Kasiun. He caused also two degrees of the meridian to be measured on the plain of Sinjar, so as to ascertain the circumference of the earth with more precision. In A.D. 824 there were held philosophical disputations in his presence. Al-Farghani was the author of an introduction to astronomy, which was printed by Golius at Amsterdam in 1669, with notes.