Ulugh Beg was a grandson of Timur (known in the West as Tamerlane), a Tartar prince and ruler of Turkestan. He was an exceptional astronomer and mathematician of the fifteenth century. Ulugh Beg was the son of Timurid king Shah Rukh and was born in 1393 at Sultaniyya in Central Asia. He was a Hafiz, someone who can recite the Qur'an by heart.
Ulugh Beg made Samarkand famous as one of the leading cities of Muslim civilization. In 1424 he built a madrasa, an institution of higher learning, where astronomy was taught. Later in 1428, Ulugh Beg began the construction of a magnificent three-story observatory in Samarkand. It was more than two hundred fifty feet in diameter and one hundred twenty feet high. He appointed Ali-Kudsi, a Muslim astronomer as the director of the Observatory. Several well-known mathematicians and astronomers including Al-Kashi and Kadizada worked there.
He equipped it with the best and most accurate astronomical instruments available then. The observatory included a Fakhri sextant (made of marble) which was used for determining the inclination of the ecliptic to the equator, the point of the vernal equinox, the length of the tropical year, and other astronomical constants measured from observation of the sun. It also included a quadrant so large that part of the ground was removed to allow it to fit in the Observatory. Other instruments included a triquetram and an armillary sphere.
In 1437 he published his most famous and enduring work, a new catalogue of stars entitled Zidj-i Djadid Sultani. In it, he revisited the positions and magnitudes of stars observed by Ptolemy. He found many errors in the computations of Ptolemy. It includes a diverse collection of observations and computations, the position of the fixed stars, the course of the stars, and the knowledge of time. An English translation of this work was published in 1917.
Ulugh Beg computed the length of the year as 365 days 5 hours 49 minutes 15 seconds, a fairly accurate value. In addition, he prepared Tables of Planetary Motions which were very popular and in demand throughout the astronomical community. Ulugh Beg studied the yearly movements of the five bright planets: Saturn, Jupiter, Mars, Venus, and Mercury. His data are still considered very accurate. In 1437, he also compiled a star catalogue giving the positions of 992 stars. His compilation of tables of sines and tangents at one-degree intervals are accurate to eight decimal places.
Ulugh Beg was assassinated in 1449 in Samarkand after a brief reign as ruler of Turkestan for three years. This catastrophe led to the neglect of the observatory and Samarkand slowly phased out as the leading center of astronomy. The observatory was eventually destroyed and its location was confirmed in 1908 by Russian archaeologists. Beer and Madler in their famous work Der Mond (1837) mention a surface feature of the moon after Ulugh Beg. It is the name of a prominent elliptical ring in the northwest of the Eighteenth section.