c. 1260

Large Medieval Observatories

Nasīr al-Dīn al-Tūsī (1201–1274), Hülegü Khan (c. 1217–1265), Ulūgh Beg (1394–1449)

It is easy to think of astronomical observatories as modern-day inventions—enormous domes on high mountains, with giant telescopes and high-tech computer equipment. But the concept of the observatory as a research institute and a shared access facility for teams of astronomers can trace its roots back to the first astronomical observatories that were established in the Islamic world and China in the Middle Ages.

Among the first major observatories in the world was the Marāgheh Observatory in northwestern Iran, established in 1259 by the Mongol ruler Hülegü Khan (grandson of Genghis) and directed by his court astronomer and mathematician Nasīr al-Dīn al-Tūsī. Marāgheh housed a huge library of more than 40,000 books, and al-Tūsī led a team of astronomers and students performing observations and calculations of planetary motions and Earth’s precession that would later be used by Copernicus and others as key inputs for a new heliocentric cosmology. Around the same time, Hülegü’s brother Kublai Khan established the Gaocheng Astronomical Observatory as the first such facility in China. Early Yuán dynasty (1279–1368) astronomers there made observations of the Sun and planets and used an enormous stone sundial to reckon time and more accurately determine the length of the year. Inspired by Marāgheh (which had been destroyed by earthquakes), in 1420 the Timurid astronomer and mathematician Ulūgh Beg established a university and observatory in Samarkand, in what is now Uzbekistan. Samarkand Observatory, later named Ulūgh Beg Observatory, included early astronomical instruments such as astrolabes and armillary spheres and a giant stone sextant/meridian circle, with a radius of 131 feet (40 meters), carved into the mountainside—the largest of its kind in the world—for accurately measuring the positions of the Sun and stars. Astronomers at Ulūgh Beg updated Ptolemy’s and al-Sūfī’s star catalogs to account for precession, enabling consistently accurate predictions of eclipses and other celestial events.

The Gaocheng Astronomical Observatory in China, established in 1276.

The remains of the giant underground meridian circle, 6 feet (2 meters) wide, at Ulu¯gh Beg Observatory in Samarkand.