Ulug Beg's Observatory

one of the largest observatories of the Middle Ages; built by Ulug Beg near Samarkand circa 1430. The remains of the observatory were discovered by V. M. Viatkin in 1908. Excavations, which were completed by V. A. Shishkin in 1948, revealed the ruins of the lower part of a wall of a round building measuring about 46 m in diameter, which contained an immense marble sextant, possibly a quadrant, installed in the meridian plane. The sextant’s radius measured 40 m. Only the lower part of one of the sextant’s arcs, measuring 32° in length and graduated in degrees, was intact. The instrument was placed in a trench about 2 m wide and 11m deep that was dug into a hill; only part of it rose above ground level.

The sextant, which originally consisted of two parallel stone arcs faced with marble slabs of corresponding curvature, was used for determining astronomical constants and the coordinates of the sun, moon, and planets at the moment of their transit across the meridian. The stars were observed by means of smaller instruments, which have not been preserved. The most important work completed at the observatory— Zij-i Gurgani (New Astronomical Tables)—contains an account of the theoretical foundations of astronomy and lists the positions of 1,018 stars (published in Oxford in 1665), determined for the first time after Hipparchus and with an accuracy that remained unsurpassed until Tycho Brahe’s observations. The star catalog and planetary tables were of great importance to the development of astronomy, as were the other investigations carried out at the observatory, such as the determinations of the inclination of the ecliptic to the equator, the annual precession of the equinoxes, and the length of the tropical year. Ulug Beg’s observatory was destroyed soon after his death in 1449.