Astronomy Astronomy was also developed under the Fatimids Caliphs AI-Hakam was personally interested in astrological and astronomical
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calculations. He built on al-Mugattam an observatory to which he often rode before dawn on his gray ass. Ibn Yanus commenced his astronomical observations at about 990 A.D., by the order of al-Aziz at his well equipped observatory at Cairo. These tables were completed in 1007 and published under the name of al-Zij al-Kabir al-Hakam in honour of al-Hakam. The Zij records of eclipses and conjunctions old and new, improved values of the inclination of Ecliptic (estimated at 230 35), of the longitude of he Sun’s apogee (860 10) of the solar parallax (reduced from 3 to 2) of the procession of the Equinoxes (50” a year), and makes no reference to the erroneous conception of the trepidation of the Ecliptic, first introduced by Thabit bin Qurra in Baghdad and blindly followed by a number of later astronomers even Copernicus, until finally discarded by Tycho Brahe. The astronomical tables of Ibn Yunus bearing the name of his patron, correct the tables current at his time by original observation made with the armillary sphere and the azimuth circle.
