Ulugbeka observatory (1428-1429). It is built on one of the hills of Samarkand. It was the three-storied, covered with color tiles building of a round form with a diameter of 46 m and not less than 30 m high. In the main hall the enormous tool for observation of the Sun, the Moon and other stars of the heavenly arch was located.
Basis of observatory was the huge goniometer (a vertical circle) which radius of a circle equaled 40,212 m, and length of the arch was 63 m the main tool - a sextant - was focused with an amazing accuracy in the area of a meridian from the South on the North.

The sizes of the main tool, its successful design, scientific knowledge of Ulugbek and his colleagues provided the amazing accuracy of astronomical observations. The observatory was for the time a unique construction. After tragic death of the great astrologer of work in observatory were stopped, and from 16th century the building gradually collapsed. By 19th century at top of the hill even of the construction remains did not remain.