Ulugh Beg 15th-Century Sultan Of the Stars

Born  Sulṭāniyya, (Iran), 22 March 1394

Died  near Samarqand, (Uzbekistan), 27 October 1449

Ulugh Beg (Turkish for “great prince”) was governor of Transoxiana and Turkestan and, during the last 2 years of his life, Timurid Sultan. However, he is mostly remembered as a patron of mathematics and astronomy. In Samarqand, he founded a school and the famous astronomical observatory, where the most extensive observations of planets and fixed stars at any Islamic observatory were made. Ulugh Beg is associated with a Persian astronomical handbook (zīj) that stands out for the accuracy with which its tables were computed.

Ulugh Beg was the first‐born son of Shāhrukh (youngest son of the infamous conqueror Tīmūr or Tamerlane) and his first wife Gawharshād. He was raised at the court of his grandfather and, at the age of 10, was married to his cousin Agha Bīkī, whose mother was a direct descendent of Chingiz Khan. Thus Ulugh Beg could use the epithet Gūrgān, “royal son‐in‐law,” which had originally been used for Chingiz’s son‐in‐law.

In the years after Tīmūr’s death in 1405, Ulugh Beg became governor of Turkestan and Transoxiana, the most important cities of which were the cultural centers Samarqand and Bukhara. Although not completely divorced from affairs of state, he is better known for his interest in religion, architecture, arts, and sciences, which were fostered by the Mongols as well as by the Timurids. Ulugh Beg is said to have spoken Arabic, Persian, Turkish, Mongolian, and some Chinese. He had a thorough knowledge of Arabic syntax and also wrote poetry. Although he honored Turkic–Mongolian customs, he also knew the Quran by heart, including commentaries and citations. Ulugh Beg was also a passionate hunter.

By 1411, Ulugh Beg had developed a lively interest in mathematics and astronomy, which may have been aroused by a visit in his childhood to the remnants of the Marāgha Observatory that had been directed by Ṭūsī. In 1417, he founded in Samarqand a madrasa (religious school or college) that can still be seen on the Registan Square. At this institution, unlike other madrasas, mathematics and astronomy were among the most important subjects taught. The most prominent teacher was Qāḍīzāde al‐Rūmī, who was joined somewhat later by Kāshī.

Two extant letters by Kāshī to his father in Kāshān make clear that Ulugh Beg was personally involved in the appointment of scholars and that he was frequently present, and actively participated, in seminars, where he displayed a good knowledge of mathematical and astronomical topics. Kāshī relates how Ulugh Beg performed complicated astronomical calculations while riding on horseback. Anecdotes from other sources show that Ulugh Beg, like many other Muslim rulers, believed in astrology and fortune‐telling. He appears as a person who very much respected the scholars he appointed, and whose main objective was to reach scientific truth.

In 1420, Ulugh Beg founded his famous astronomical observatory on a rocky hill outside the city of Samarqand. Its circular main building, beautifully decorated with glazed tiles and marble plates, had a diameter of about 46 m and three stories reaching a height of approximately 30 m above ground level. The north–south axis of the main building was occupied by a huge sextant with a radius of 40 m (called Fakhrī sextant after that of Khujandī). On the scale of this instrument, which partially lay in an underground slit with a width of half a meter, 70 cm corresponded to 1° of arc, so that the solar position could be read off with a precision of 5″. On the flat roof of the main building various smaller instruments could be placed, such as an armillary sphere, a parallactic ruler, and a triquetrum. Among other instruments known to have been used in Samarqand are astrolabes, quadrants, and sine and versed sine instruments.

Although Ulugh Beg was the director of the Samarqand Observatory, Kāshī was in charge of observations until his death in 1429, after which he was succeeded by Qāḍīzāde, who died after 1440. The observational program was completed by Qūshjī, who had studied in Kirmān (southeastern Iran) before returning to Samarqand. The results of the observations made under Ulugh Beg include the measurement of the obliquity of the ecliptic as 23° 30’17” (the actual value at the time was 23° 30’48”) and that of the latitude of Samarqand as 39° 37’33” N. (modern value: 39° 40′). Furthermore, most of the planetary eccentricities and epicyclic radii were newly determined, and the longitudes and latitudes of the more than 1,000 stars in Ptolemy’s star catalogue were verified and corrected. Precession was found to amount to 51.4″ per year (corresponding to 1° in little more than 70 years; the actual value is 50.2″ per year).

The observatory of Ulugh Beg stayed in operation for little more than 30 years. It was finally destroyed in the 16th century and completely covered by earth in the course of time. In 1908, archaeologist V. L. Vyatkin recovered the underground part of the Fakhrī sextant, consisting of two parallel walls faced with marble and the section of the scale between 80° and 57° of solar altitude. Ulugh Beg’s observatory exerted a large influence on the huge masonry instruments built by Jai Singh in five Indian cities (most importantly Jaipur and Delhi) in the 18th century, more than 100 years after the invention of the telescope.

The main work with which Ulugh Beg is associated is an astronomical handbook with tables in Persian, variously called Zīj‐i Ulugh Beg, Zīj‐i Jadīd‐i Sulṭānī, or Zīj‐i Gūrgānī. In the introduction, Ulugh Beg acknowledges the collaboration of Qāḍīzāde, Kāshī, and Qūshjī, who were undoubtedly responsible for the underlying observations as well as the computation of the tables. The Zīj is in many respects a standard Ptolemaic work without any adjustments to the planetary models. It consists of four chapters dealing with chronology, trigonometry and spherical astronomy, planetary positions, and astrology, respectively. The instructions for the use of the tables, which were edited and translated into French by L. Sédillot in the middle of the 19th century, are clear but very brief and do not even include examples of the various calculations.

Thus, the most significant part of Ulugh Beg’s Zīj lies in the observations and computations underlying the tables. Most impressively, the sine table, covering 18 pages in the manuscript copies, displays the sine to five sexagesimal places (corresponding to nine decimals) for every arc minute from 0° to 87° and to six sexagesimal places (11 decimals) between 87° and 90°. All independently calculated values for multiples of 5′ are correct to the precision given, whereas the intermediate values, calculated by means of quadratic interpolation, contain incidental errors of at most two units. Also most of the planetary tables in the Zīj were calculated to a higher precision than before. New types of tables were added that simplified the calculation of planetary positions. Ulugh Beg’s star catalog for the year 1437 represents the only large‐scale observations of star coordinates made in the Islamic realm in the medieval period. (Most other catalogs simply adjusted Ptolemy’s ecliptic coordinates for precession or were limited to a relatively small number of stars.)

Ulugh Beg’s Zīj was highly influential and continued to be used in the Islamic world until the 19th century. It was soon translated into Arabic by Yaḥyā ibn ʿAlī al‐Rifāʿī and into Turkish by ʿAbd al‐Raḥmān ʿUthmān. Reworkings for various localities were made in Persian, Arabic, and Hebrew by scholars such as ʿImād al‐Dīn ibn Jamāl al‐Bukhārī (Bukhara), Ibn Abī al‐Fatḥ al‐Ṣūfī (Cairo), Mullā Chānd ibn Bahāʾ al‐Dīn and Farīd al‐Dīn al‐Dihlawī (both Delhi), and Sanjaq Dār and Husayn Qusʿa (Tunis). Commentaries to the Zīj were written by Qūshjī, Mīram Chelebī, Bīrjandī, and many others. Hundreds of manuscript copies of the Persian original of Ulugh Beg’s Zīj are extant in libraries all over the world. Already in 17th‐century England, various parts of the Zīj were published in edition and/or translation.

Little is known about other works of Ulugh Beg. A marginal note by him in the India Office manuscript of Kāshī’s Khāqānī Zīj presents a clever improvement of a spherical astronomical calculation. A Risāla fī istikhrāj jayb daraja wāḥida (Treatise on the extraction of the sine of 1°) has been attributed to Ulugh Beg on the basis of a citation in Bīrjandī, although most manuscripts of this work mention Qāḍīzāde as the author. Aligarh Muslim University Library lists a treatise Risāla‐yi Ulugh Beg that is yet to be inspected. Finally, an astrolabe now preserved in Copenhagen and made in 1426/1427 by Muḥammad ibn Jaʿfar al‐Kirmānī, who is known to have worked at the observatory in Samarqand, was originally dedicated to Ulugh Beg.

In 1447, Ulugh Beg succeeded his father Shāhrukh as sultan of the Timurid empire. However, he was killed on the order of his son ʿAbd al‐Laṭīf. An investigation of Tīmūr’s mausoleum by Soviet scholars in the 1940s showed that Ulugh Beg was buried as a martyr in accordance with Sharīʿa (Islamic law), i. e., fully clothed in a sarcophagus

Ulugh Beg was a Timurid ruler as well as an astronomer, mathematician. His primary interest was in the sciences and intellectual matters. 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. Ulugh Beg was also notable for his work in astronomy-related mathematics, such as trigonometry and spherical geometry. He built the great Ulugh Beg Observatory in Samarkand, which was considered by scholars to have been one of the finest observatories in the Islamic world at the time and the largest in Central Asia.


Statue of Ulugh Beg and his students, Registan square, Samarqand, Uzbekistan (Image Source)


Ulugh Beg, statue in Riga, Latvia (Image Source)

Muhammad Taraghāy ibn Shāhrukh ibn Tīmūr, known as Ulugh Beg

Born in Sultāniyya (Iran) on 22 March 1394

Died near Samarqand (Uzbekistan) on 27 October 1449

Muhammad Taraghāy ibn Shāhrukh ibn Tīmūr better known as Ulugh Beg (Sultāniyya (Iran) on 22 March 1394 and died near Samarqand (Uzbekistan) on 27 October 1449) was a Timurid ruler as well as an astronomer, mathematician. Ulūgh Beg was the grandson of the Asian conqueror Timur (Tamerlane). His primary interest was in the sciences and intellectual matters. Under his brief rule the Timurid dynasty reached its cultural peak. His father, Shāh Rokh, captured the city of Samarkand and gave it to Ulūgh Beg, who made it a centre of Muslim culture. There he wrote poetry and history and studied the Qur?ān. His greatest interest was astronomy, and he built an observatory (begun in 1428) 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 also notable for his work in astronomy-related mathematics, such as trigonometry and spherical geometry. He built the great Ulugh Beg Observatory in Samarkand, which was considered by scholars to have been one of the finest observatories in the Islamic world at the time and the largest in Central Asia. He also build the Ulugh Beg Madrasah (1417–1420) in Samarkand and Bukhara, transforming the cities into cultural center of learning in Central Asia.

In a long and detailed article on Astronomical Observatories in the Classical Islamic Culture, FSTC Research Team devoted a section to The Legacy of Ulugh Beg that we reproduce to celebrate the anniversary of this great scholar.

The Legacy of Ulugh Beg

In a noteworthy article by Kevin Krisciunas (University of Notre Dame, Department of Physics) on The Legacy of Ulugh Beg, the author presents an outline on the subject of Muslim observatories and especially the work performed in Samarqand observatory [1].

Figure: Remains of Jaipur observatory in India built by Maharajah Jai Singh in 1726. Early observations were carried out by the naked eye from the top of this monumental architectural structures. The monuments include a massive sundial, the Samrat Yantra, and a gnomon inclined at 27m , showing the altitude of Jaipur and the height of Pole Star. There is also a large astronomical sextant and a meridian chamber. (Source).

Krisciunas reminds us that Ulugh Beg is to be remembered not for his princely role, but for his role as patron of astronomy, an astronomer and observatory builder. His distinction was that he was one of the first to advocate and build permanently mounted astronomical instruments. The importance of his observatory is further enhanced by the large number of astronomers, between sixty and seventy, involved in observation and seminars. Of crucial importance, too, is that observations were carried on a systematic basis forlengthy periods of time, as from 1420 to 1437. The reason, as Krisciunas makes clear, why observations are not completed in one year but instead require ten or fifteen years, is:

“The situation is such that there are certain conditions suited to the determination of matters pertaining to the planets, and it is necessary to observe them when these conditions obtain. It is necessary, e.g., to have two eclipses in both of which the eclipsed parts are equal and to the same side, and both these eclipses have to take place near the same node. Likewise, another pair of eclipses conforming to other specifications is needed, and still other cases of a similar nature are required. It is necessary to observe Mercury at a time when it is at its maximum morning elongation and once at its maximum evening elongation, with the addition of certain other conditions, and a similar situation exists for the other planets.

“Now, all these circumstances do not obtain within a single year, so that observations cannot be made in one year. I is necessary to wait until the required circumstances obtain and then if there is cloud at the awaited time, the opportunity will be lost and gone for another year or two until the like of it occurs once more. In this manner, there is a need for ten or fifteen years. One might add that because it takes Saturn 29 years to return to the same position amongst the stars (that being its period of revolution about the Sun), a period of 29 years might have been the projected length of the Samarkand programme of observations.”

In his article, Krisciunas, although recognising the crucial role of Islamic observation, still finds sources of disagreement with the notion that the Samarqand observatory exerted decisive influence on Europe. Actually, the legacy of this scientific institution was indeed not transmitted to the West, where a thriving scientific tradition was being developed as a result of earlier contacts with Arabic science. It remains true, however, that the work of Ulugh Beg and his colleagues had an important impact on another Islamic team of scholars, those who worked in Istanbul in late 16th century under the leadership of Taqi al-Din ibn Ma’ruf. Now, the similarity of Taqi al-Din’s astronomical instruments with those of Tycho Brahe is amazing, and should stand as a strong evidence that the Danish astronomer certainly knew in a way or another of the achievements of his Muslim colleagues, at least in the field of astronomical instrumentation [2].


“The Samarkand observatory consisted of a monumental cylindrical building of a height of 30 meters and a diameter of 46, with a huge marble sextant, the “Sextant of Fakhri”, of a radius of about 40 meters, allowing a very high precision in the astronomical measurements during the passage of the Sun, the Moon or the planets along the meridian. This arch of 60° included staircases on each side to allow the assistants carrying out the measurements to move.” (Source)

End Notes

[1] Kevin Krisciunas, “The Legacy of Ulugh Beg”, Bulletin of the Association for the Advancement of Central Asian Research, vol. 5, no. 1, Spring 1992, pp. 3-6. Reprinted in in Central Asian Monuments, edited by Hasan B. Paksoy, Istanbul: Isis Press, 1992, pp. 95-103 (for an online version click here). See also by the same author: “The accuracy of the measurements in Ulugh Beg’s star catalogue”, Bulletin of the American Astronomical Society, vol. 24, no. 4, 1992, 1166-7; “A more complete analysis of the errors in Ulugh Beg’s star catalogue”, Journal for the History of Astronomy, vol. 24, November 1993, pp. 269-280; and “Observatories”, Encyclopedia of Astronomy and Astrophysics, Institute of Physics Publishing, 1999 (available on The astrophysics preprint server: arXiv:astro-ph/9902030.

[2] This issue is studied by Sevim Tekeli, The Instruments of Istanbul Observatory (published on www.MuslimHeritage.com, 8 June 2008). See also Aydin Sayili, Observatories In Islam and Salim Aydüz, Ottoman Contributions to Science and Technology: Examples from Geography and Astronomy.


Samarkand, Uzbekistan​ (Image Source)

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