Ulugbek Observatory

In the 15th century there were no telescopes; astronomers measured the sky with instruments whose accuracy depended on their size. Ulugbek therefore built big. His observatory was a round building of three storeys, roughly 46 metres in diameter and about 30 metres high, standing on a rocky hill outside the city. Its main instrument was a meridian arc, often called the Fakhri sextant, with a radius of about 40 metres, set exactly along the north–south line. Part of it was cut into the rock below ground, and part rose through the building.

Astronomers observed the sun, moon and stars as they crossed the meridian and read their positions on scales marked along the arc. Other instruments, including astrolabes and armillary spheres, stood on the upper floors. The walls were reportedly decorated with images of the heavens and the earth.

The work of Ulugbek and his team, including Qazi-zada Rumi, Ghiyath al-Din al-Kashi and later Ali Qushji, was published as the Zij-i Sultani, a set of astronomical tables. Its star catalogue gave the positions of 1,018 stars, the first new catalogue of this scale since Ptolemy, more than a thousand years earlier. The observatory also calculated the length of the sidereal year as 365 days, 6 hours, 10 minutes and 8 seconds, within about a minute of modern values, and measured the tilt of the Earth’s axis with similar precision.

The tables were copied across the Islamic world, translated into Latin in the 17th century and studied in Oxford. A crater on the Moon is named after Ulugbek.

Ulugbek was overthrown and killed in 1449. Conservative religious circles that had opposed his interest in science gained influence, and the observatory was abandoned and gradually dismantled for its bricks. Ali Qushji took copies of the tables to Herat and later to Istanbul, where they survived.

For more than four centuries the site was lost. In 1908 the archaeologist Vasily Vyatkin, studying old documents describing the land, found the location and excavated the underground part of the arc. Vyatkin loved the site so much that he asked to be buried there; his grave is beside the museum.

A modern entrance building leads to the excavated trench, where the curved marble-lined rails of the meridian arc descend steeply underground. You look down into it from a covered platform; it is the only part of the instrument that survives, but its scale gives a sense of the original. Outlines in the ground show the circular plan of the observatory.

The museum next to it displays copies of the star catalogue, miniatures showing astronomers at work, models of the building and instruments, and exhibits about Ulugbek’s life. A statue of Ulugbek stands in front. Labels are usually in Uzbek, Russian and English.

The observatory is on the Tashkent road north-east of the old city, about 10 minutes by taxi from the Registan or a 15-minute drive from Shah-i-Zinda. A ticket is required. Morning and late afternoon are best in summer, as the hilltop is exposed. Combine it with the Afrasiyab museum and the Tomb of Daniel, which are on the way back towards the centre.

The observatory makes most sense as part of a day following Ulugbek through the city: his madrasah on the Registan, where astronomy was taught; the observatory, where his scholars worked; and his tomb in Gur-Emir, beside his grandfather Timur. Few rulers of the time combined political power with real scientific achievement, and Samarkand is proud of him. His name is found on schools, streets and the modern astronomical institute in Tashkent.