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an astronomical observatory built in the second half of the 13th century in the city of Maragheh (eastern Azerbaijan Province, Iran) and existing to the mid-14th century. More than 100 scholars from different countries worked at the observatory at various times. The astronomical catalog al-Zij al-Il-Khani compiled at the observatory under the direction of Nasir al-din al-Tusi contained the most precise tables of that time of the motions of planets and the positions of stars, as well as six-place tables of trigonometric functions and a list of the geographic coordinates of 256 cities of the world. Of the ten large astronomical instruments used at the observatory, five were of unique design. The observatory’s library contained more than 400,000 manuscripts.