Timurid ruler and astronomer Ulugh Beg (1394-1449) built one of the earliest Islamic astronomical observatories in the fifteenth century, on the Chupan-Ata plateau, amidst ruins of the ancient city of Afrasiyab, on the outskirts of Samarkand. Foundations of the three story cylindrical structure and underground sections of a giant marble sextant were unearthed by Russian archaeologist Vladimir Viatkin in 1908. Famed medieval astronomers such as Ghiyas al-din Jamshid and Kazy-zadeh Rumi are recorded to have worked at this observatory until Ulugh Beg's assassination in 1449, after which the institution was vandalized. The observatory appears to have been influenced in its plan and arrangement of instruments by the earlier observatory of Nasir al-Din Tusi (1201-1274) at Marageh, built by Hulagu Khan (1217-1265) in 1258.
The observatory consisted of three gigantic astronomical instruments that dictated the building's structure and layout, while service rooms occupied the residual space. The primary instrument was a colossal meridian arc or sextant (suds-i fakhri), running through the building's center, placed along the north-south axis. This quadrant, with incised Arabic symbols and numerals on white marble slabs was partly hewn into rock, while the upper part of its brick arc structure reached the flat roof of the observatory, at the height of forty meters. The solar clock (i'tidal) is described by Muhammad Husain al- Birjandi in his astronomical tract, Sharh al-Tadhkira (1507), to have consisted of a wall with concave profile built perpendicular to the sextant, along the east-west axis. This arrangement allowed the sextant to act as the clock's gnomon and cast shadows on its curving wall.
Famed medieval scientist Al-Biruni (973-1048) described the third major instrument as a rotating quadrant sector (ustuvan). The rooftop was itself incised with a grid that served as an azimuthal circle, so that the azimuth of luminaries could be recorded through the arcades along the roof's parapet. The central sextant divided the observatory into northern and southern halves; rooms in the northern section were cruciform in plan while the southern section had rectangular rooms. Service rooms were clustered on the ground floor, with few openings except an entry from the south, above which an arcaded gallery ran the entire circumference of the building, forty-eight meters in diameter.
In the absence of much physical evidence, descriptions by historian Abd al-Razzak Samarkandi (1413-1482), mathematician like Ghiyath al-Din Jamshid Kashi (1380-1429) and Timurid ruler like Babur (1483-1530) help us understand stages of the observatory's construction, its function and its demise. Based on their descriptions, the building was decorated with glazed brick mosaics, on the exterior and the interior had paintings depicting the position, orbit and physical characteristics of heavenly bodies. A second major excavation in 1941, led by B.N. Zasipkin produced hypothetical reconstructions of the observatory. Their theories were refined in further investigations of neighboring sites in 1965-67 by Uzbek archaeologist Galina Pugachenkova. Today, tourists throng a cylinder shaped museum dedicated to Ulugh Beg near the observatory's excavated plinth.
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