On March 22, 1394, Mongolian astronomer, mathematician and sultan Mīrzā Muhammad Tāraghay bin Shāhrukh, better known as Ulugh Beg was (probably) born. Although the only important Mongol scientist, he was the greatest astronomer of his time. Pursuing this interest he built an observatory at Samarkand. In his observations he discovered a number of errors in the computations of the 2nd-century Alexandrian astronomer Ptolemy, whose figures were still being used.
Ulugh Beg was the grandson of the conqueror Timur. After Timur’s death, the empire was disputed among his sons including Skah Rukh, Ulugh Beg’s father. Starting from 1407, he controlled a great part of the empire including Iran and Turkistan regaining control of Samarkand. Two years later, Shah Rukh decided to make Herat in Khorasan his new capital and made it a center of trade and culture while Samarkand was given to Ulugh Beg, who was highly interested in making the city a cultural centre instead of dealing with politics and the military. [1,3]
It is believed that already in his early years, Ulugh Beg was interested in science, especially astronomy. He visited the remains of Maragha Observatory in his younger years.  However, Ulugh Beg also never neglected the arts, writing poetry himself and studying history. He built a center for higher education, especially mathematics, which was completed in 1420. Ulugh Beg began to appoint the best scientists he could find to positions there as lecturers. [1,2]
Al-Kashi became one of the leading figures of the scientific life of Samarkand and in his letters, he praised the mathematical achievements of Ulugh Beg, who led scientific meetings where problems in astronomy were freely discussed.  Soon, Ulugh Beg started to built an astronomy at Samarkand and the construnction works probably began in 1428. The observatory was over 35 meters high and 50 meters in diameter. [1,2]
The scientists working at the observatory were able to find methods for giving accurate approximate solutions of cubic equations and work with the binomial theorem. Also, Ulugh Beg’s accurate tables of sines and tangents correct to eight decimal places were established and formulae of spherical trigonometry were found. Further, Ulugh Beg’s Catalogue of the stars, the first comprehensive stellar catalogue since that of Ptolemy counts to one of their greatest achievements. 
The star catalogue, the Zij-i Sultani, was published in 1437 and gives the positions of almost 1000 stars. The catalogue was accomplished by Ulugh Beg himself, al-Kashi, and Qadi Zada. The work contained tables of observations made at the Observatory, calendar calculations and results in trigonometry. Further, several mistakes in the calculations of Ptolemy were found and with the help of the new findings, Ulugh Beg was able to calculate the length of the year as 365 days 5 hours 49 minutes 15 seconds. [1,2]
Unfortunately, after the death of Ulugh Beg’s father in 1447, he could not retain power and was put to death. In 1941, his tomb was discovered in the mausoleum built by Timur in Samarkand. [1,3]
At yovisto you can learn more about today’s telescope technologies in a lecture by Roy Gould.
References and Further Reading:
-  Ulugh Beck Biography at MacTutor History
-  Ulugh Beg at the Portal to the Heritage of Astronomy
-  The Ulug Beck Observatory