Successful in his quest for knowledge, Ulugh Beg was ultimately unsuccessful as a ruler and a politician. Religious conservatives distrusted him, and he was assassinated in 1449 by his own son. Soon after death, his observatory was so thoroughly destroyed by religious conservatives that there was no trace left above ground, and its location was a mystery for centuries. In 1908 an amateur archaeologist, Vladimir Vyatkin, determined its likely location from searching ancient manuscripts and unearthed the sextant on Kukhak Hill, northeast of Afrasiab. The underground arc of the quadrant, made of brick clad in marble, is still there, protected by an unassuming tunnel-like building.
Visitors can walk down stone steps into the earth to get a closer look.
Calculations were made using a huge astrolabe mounted on metal rails on either side of the quadrant. There's a small museum nearby, mostly about the lives of Timur and Ulugh Beg. It doesn't contain a lot of artifacts but has some informative exhibits and models of the observatory. Afrasiab Afrasiab, the pre-Mongol city, is now merely a large plateau of yellow loess, maybe half a mile northeast of the Registan, past the Bibi Khanum mosque. The Tashkent Road, heedless of artifacts, runs through it, and from a distance it looks like nothing more than a huge, desultory urban earthwork.