The Legacy of Ulugh Beg

Kevin Krisciunas[1]

Muhammed Taragai Ulugh Beg (1394-1449) was a Turk who ruled the province of Transoxiana (Maverannahr), a region situated between the River Oxus (Amu Darya) and the River Jaxartes (Syr Darya), the principal city of which was Samarkand. Ulugh Beg's grandfather was the famous conqueror Timur (1336-1405). Ulugh Beg became the ruler of Transoxiana in 1447 upon the death of his father. But his rule was of short duration. Two years later he was killed by an assassin hired by his son 'Abd al Latif.

Were it only for his role as prince, viceroy, and martyr, few scholars would know of Ulugh Beg. But his memory lives on because he was an observatory builder, patron of astronomy, and astronomer in his own right. He was certainly the most important observational astronomer of the 15th century. He was one of the first to advocate and build permanently mounted astronomical instruments. His catalogue of 1018 stars (some sources count 1022) was the only such undertaking carried out between the times of Claudius Ptolemy (ca. 170 A.D.) and Tycho Brahe (ca. 1600). And, as we shall briefly discuss here, his attitude towards scientific endeavors was surprisingly modern. The administration of Transoxiana was the responsibility of Ulugh Beg's father for most of Ulugh Beg's life. The prince had the opportunity (and the inclination) to pursue scholarly matters. His interest in astronomy dates from an early age, when he visited the remains of the Maragha Observatory, made famous by the astronomer Nasir al-Din al-Tusi (1201-74). The principal accomplishment at Maragha was the Zij-i ilkhani, or Ilkhanic Tables.[2]

A principal source of our information about the astronomical activity at Samarkand is a letter of one Ghiyath al-Din Jamshid al-Kashi (d. 1429), which is available in Turkish and English (see Sayili 1960). This letter, originally in Persian, was written in 1421 or 1422. From it we deduce that serious astronomical activity began in Samarkand in 1408-10, and that the construction of Ulugh Beg's observatory was begun in 1420. Amongthe astronomers known to have been active at Samarkand, we know only a few by name, but according to al-Kashi there were sixty or seventy scholars at the madrasa who were well enough versed in mathematics to participate in some capacity in the astronomical observations and/or seminars.

The observations were carried out systematically from 1420 to 1437. While observatories today are expected to carry on indefinitely, this was not the case in olden times. Rather, observations were carried out, for example, to update tables of planetary motions in order to predict their future positions. al-Kashi tells us (see Sayili 1960, p.106):

As to the inquiry of those who ask why observations are not completed in one year but require ten or fifteen years, 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. It 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 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 program of observations. A number of instruments were used for the observations of the planets and for determining the relative positions of the stars.[3] The largest instrument in Samarkand was the so-called Fakhri sextant. It was a 60-degree stone arc mounted on the north-south meridian line. Such an instrument was used to determine the transit altitudes of stars (i.e. their maximum angular distances above the horizon). From the most southern and northern positions of the Sun, observed over the course of a year, one can easily determine the obliquity of the ecliptic (i.e. the tilt of the Earth's axis of rotation with respect to the plane of its orbit.) The mean of these extrema, or the meridian altitude of the Sun at the moment of the vernal or autumnal equinox allows one (by definition) to determine one's latitude.[4] According to Ulugh Beg the obliquity of the ecliptic was 23 degrees 30' 17" (differing by only 32" from the true value for his time). His value for the latitude of Samarkand was 39 degrees 37' 33". Now, to the reader unaccustomed to astronomical topics, these might seem like just numbers, the accuracy of which may mean nothing. The most interesting thing about the Fakhri sextant in Samarkand was that its radius was 40 meters! (This is very nearly equal to the height of the dome of the 200-inch reflector at Palomar Mountain, California.) The Fakhri sextant was by far the largest meridian instrument ever built. It could achieve a resolution of a several seconds of arc -- on the order of a six-hundredth of a degree, or the diameter of an American penny at a distance of more than half a kilometer. Because the Fakhri sextant was an arc fixed on the meridian,it could only be used for determining the declinations of celestial bodies. (This being before the invention of accurate clocks, it could not be used for the determinations of relative right ascensions.) Because it was a 60-degree arc, it could not be used to observe stars along the full north-south meridian. Thus, it could not be used, say, to determine the angular separations of pairs of stars, or for observing stars near the northern or southern horizons. Consequently, other observational instruments were used at Samarkand, among them parallactical lineals and equinoctial and solstitial armillary spheres. These were made of metal and wood and were on the order of 1 meter in size. Hand held astrolabes are not to be included in this list because they were "star finders" and were used for rough time determination, rather than for the accurate determination of stellar or planetary positions. Typically, two people were required to make individual observations at any given time. At Samarkand it was the practice for a larger number of people to discuss the results. In modern terms, this is like peer review, the purpose of which is to eliminate sources of error and to ensure the health of the observational program. Ulugh Beg himself has allowed that in scientific questions there should be no agreeing until the matter is thoroughly understood and that people should not pretend to understand in order to be pleasing. Occasionally, when someone assented to His Majesty's view out of submission to his authority, His Majesty reprimanded him by saying 'you are imputing ignorance to me.' He also poses a false question, so that if anyone accepts it out of politeness he will reintroduce the matter and put the man to shame.[5]

The foreword to Ulugh Beg's Zij contains four parts: 1) the chronology, describing various systems of time reckoning; 2) practical astronomy (how observations are made and used); 3) the apparent motions of the Sun, Moon, and planets, based on a geocentric system of the universe; and 4) astrology. Besides the tables of motions of the Sun, Moon, and planets,Ulugh Beg's Zij was significant for its catalogue of about 1000 stars, giving their names and ecliptic coordinates. In an appendix to this paper I give a list of published works that contain all or part of Ulugh Beg's Zij.[6] In Flamsteed's Historia Coelestis Britannica (1725) and Baily's 1843 treatise we can directly compare Ulugh Beg's positions with those of Ptolemy,Tycho Brahe, and others. With modern stellar positions, proper motions, and an accurate treatment of precession, it would be interesting to make a statistical analysis of, say, the 100 brightest stars, to see how these catalogues compare as to average accuracy.[7]

In The Observatory in Islam Sayili concludes (pp. 391, 393) by stating:

The observatory as an organized and specialized institution was born in Islam; it went through very important stages of evolution within Islam itself; it passed on in a rather highly developed state to Europe, and this was followed, shortly afterwards, by the creation of modern observatories of Europe, in an unbroken process of evolution superposing upon the traditions borrowed from Eastern Islam...The question is of the case of the Samarqand Observatory because it appears as probably the most important Islamic observatory from the standpoint of influences exerted upon Europe.

I can accept the first half of Sayili's perspective. The astronomical programs carried out at Baghdad (9th century), Cordova (10th century), Cairo (10th to 12th centuries), Toledo (11th century), Castile (under the Christian King Alfonso X; 13th century), Maragha (13th century), and at Samarkand (15th century) were far more extensive than anything carried out by the ancient Greeks, with the possible exception of Hipparchus. The Arabs honored learning and kept alive the study of astronomy by preserving Ptolemy's Almagest and adding to its mathematical formulation. The Ma'munic, Hakemite, Toledan, Ilkhanic and Alphonsine Tables, along with the tables contained in Ulugh Beg's Zij have come down to us because scholars knew they were important. But the influence of the Samarkand Observatory on European astronomy was more indirect than direct. While copies of Ulugh Beg's Zij existed in various libraries such as Oxford and Paris not long after its composition (see Razvi 1985), it only became known in Europe in the mid-17th century, nearly five decades after the publication of Tycho Brahe's much more accurate data (see appendix to this paper).

If the activities in Samarkand influenced European ones, why does Ulugh Beg only get cursory mention (on pp. 328 and 347, but not in the index) of Dreyer's classic 1890 biography of Tycho Brahe? In Thoren's even more authoritative 1990 biography of Tycho there is no mention of Ulugh Beg at all. It was work such as Tycho's, not Ulugh Beg's, that led in turn to the efforts at Greenwich (founded 1675), Pulkovo (founded 1839), and the United States Naval Observatory (founded 1844), among other institutions, and these modern, national, facilities did not need or use Ulugh Beg's work as a fundamental component of the construction of accurate star catalogues. Yet, to be fair, astronomers and historians have found many uses for ancient and medieval observations, such as studies of the spin down rate of the Earth, studies of the motion of the Moon and planets, and the dating of historical events. Ulugh Beg's observations being the best of their century allow them to stand as a permanent observational archive for our benefit. For example, Shcheglov (1977) has recently used information from the modern excavation of Ulugh Beg's large meridian instrument for a study of continental drift. The most direct influence of the Samarkand Observatory was on the construction of the five observatories, or Jantar Mantars, built by Maharajah Jai Singh (1686-1743) in India. Jai Singh was a Hindu prince in the court of a Muslim Mogul emperor. These observatories were built at New Delhi, Ujjain, Mathura, Varanasi, and Jaipur. The largest instrument was 27 meters high. For more information see Kaye (1918), Mayer (1979), Sharma (1987), and Bedding (1991). While recognition of Ulugh Beg's contributions to astronomy was delayed, an extensive body of information now exists on the activity of his observatory in Samarkand.[8] We now know that at the time Ulugh Beg's observatory flourished it was carrying out the most advanced observations and analysis being done anywhere. In the 1420's and 1430's Samarkand was the astronomical capital of the world. As such it is deserving of further study.


[1] Member, International Astronomical Union, Commission 41 (History of Astronomy).

[2] A zij is an astronomical treatise that usually contains tables for calculating the positions of the Sun, Moon, and planets. It might also contain a star catalogue.

[3] For a discussion of the astronomical instrumentation of the Arabs, see Sedillot (1841), Repsold (1908), and Krisciunas (1988,chapter 2). Note that the telescope was only first used for astronomical purposes in 1609.

[4] Strictly speaking, one must also account for atmospheric refraction. For a review of astronomical coordinate systems see Krisciunas (1988, chapter 1).

[5] Sayili (1960, pp. 109-110).

[6] The appendix is largely based on information found in Shcheglov (1968; 1979) and in the National Union Catalog Pre-1956 Imprints. I thank Paul Luther for additional information.

[7] Vogt (1925) found 22' for the average error of 122 Ptolemaic celestial latitudes. The best of Tycho's stellar positional measures are good to 1'. See Dreyer (1890, pp.387-8), Wesley (1978), and Thoren (1990, pp. 287-299, and references therein).

[8] See Kary-Niiazov (1967) and Sirazhdinov (1979).


Barthold, W. W., Ulugh Beg und seine Zeit. Abhandlungen fur die Kunde des Morganlandes 21, No. 1, 1935.

Bedding, James, "Playground for the stars: The Jantar Mantars, Astronomical Observatories in India," New Scientist, 31 August 1991, p. 49.

Dreyer, J. L. E., Tycho Brahe: A Picture of Scientific Life and Work in the Sixteenth Century (Gloucester, Mass.:Peter Smith), 1977 reprint. (Original edition published by Adam & Charles Black, Edinburgh, 1890.)

Kar[y]-N[i]iazov, T. N., "Ulugh Beg", in Dictionary of Scientific Biography 13, pp. 535-537.

Kary-Niiazov, T. N., Astronomicheskaia shkola Ulugbeka, (Tashkent), 1967.

Kaye, G. R., The Astronomical Observatories of Jai Singh, (Janpath, New Delhi: Archaeological Survey of India), reprint of 1918 edition.

Krisciunas, Kevin, Astronomical Centers of the World (Cambridge: Cambridge Univ. Press), 1988.

Mayer, Ben, "Touring the Jai Singh Observatories," Sky and Telescope 58, No. 1, July 1979, pp. 6-10.

Razvi, Abbas, "The Observatory at Samarqand (Marsad-e-Ulugh Beg, 15th C)," Central Asia, No. 17, 1985, pp. 97-150.

Repsold, Johann A., Zur Geschichte der Astronomischen Mess-werkzeuge von Purbach bis Reichenbach (1450 bis 1830) (Leipzig: Wilhelm Engelmann), 1908. I have a rough (unpublished) English translation, which I would be happy to provide anyone, of the first six sections of this work, covering the astronomical instrumentation of the ancient Greeks, the Arabs, Purbach, Regiomontanus, Copernicus, Apian, Wilhelm IV of Hesse-Cassel, and Tycho Brahe.

Sarton, George, Introduction to the History of Science (Baltimore: Williams & Wilkins), 1948, vol. 3, pp. 1120, 1467-1474.

Sayili, Aydin, Ulug Bey Ve Semerkanddeki Ilim Faaliyeti Hakkinda Giyasuddin-i Kasi'nin Mektubu (Ghiyath al Din al Kashi's Letter on Ulugh Bey and the Scientific Activity in Samarqand) (Ankara: Turk Tarih Kurumu Basimevi), 1960. In note 1, pp. 32-33 of this work it is stated that another English translation was published by E. S. Kennedy (Orientalia 29, 1960, pp. 191-213), which differs in many particulars, and that the Persian text of the letter was published twice before that.

Sayili, Aydin, The Observatory in Islam and its Place in the General History of the Observatory (New York: Arno Press), 1981 reprint. (Original edition published by Turk Tarih Kurumu Basimevi, Ankara, 1960.)

Sedillot, L. [P. E. A.], Memoire sur les instruments astron. des Arabes, Paris, 1841.

Sharma, V. N., "The Astronomical Efforts of Sawai Jai Singh," in G. Swarup [et al.], eds., History of Oriental Astronomy (Cambridge: Cambridge Univ. Press), 1987, pp. 233-240.

Sh[ch]eglov, V. P., Jan Hevelius: The Star Atlas (Tashkent: "Fan" Press), 1968.

Shcheglov, V. P., "Astronomical azimuths of terrestrial objects as indicators of the rotational motions of the continental blocks," Soviet Astronomy 21, No. 4, July-August 1977, pp. 499-502.

Shcheglov, V. P., "Rasprostranenie <> v evropeiskoi pechati," in Sirazhdinov (1979, see below), pp. 143-151.

Sirazhdinov, S. KH., ed., Iz istorii nauki epokhi Ulugbeka, (Tashkent: Academy of Sciences of the Uzbek SSR), 1979.

Thoren, Victor E., The Lord of Uraniborg: A Biography of Tycho Brahe (Cambridge: Cambridge University Press), 1990.

Vogt, H., "Versuch einer Wiederherstellung von Hipparchs Fixsternverzeichnis," Astronomische Nachrichten, No. 5354-55 (1925):23.

Wesley, Walter, "The accuracy of Tycho Brahe's instruments," Journal for the History of Astronomy 9 (1978), pp.42-53.


1648. John Greaves (1602-1652). Quibus accesserunt, Insigniorum aliquot Stellarum Longitudines, et Latitudines, Ex Astronomicis Observationibus Ulug Beigi, Tamerlani Magni Nepotis. Oxoniae. Contains latitudes and longitudes of [98] stars.

1648. John Greaves (1602-1652). Binae Tabulae Geographicae, una Nassir Eddini Persae, altera Vlug Beigi Tatari: Opera et Studio J. Gravii. Lugduni, Batavorum. Geographical tables of the Zij.

1648. John Bainbridge (1582-1643). Canicularia. Una cum demonstratione ortus Sirii heliaci, pro parallelo inferioris Aegypti. Auctore Iohanne Gravio. Quibus accesserunt, insigniorum aliquot stellarum longitudines, et latitudines, ex astronomicis observationibus Vlug Beigi. Oxoniae, H. Hall. The citation in the U. S. Naval Observatory copy states that Greaves added the catalogue of 98 Ulugh Beg stars to the Bainbridge treatise.

1650. John Greaves (1602-1652). Epochae Celebriores, Astronomis, Historicis, Chronologis, Chataiorum, Syro-Graecorum Arabum, Persarum, Chorasmiorum usitatae (Arabice et Latine): Ex traditione Ulugi Beigi; eas primus publicavit, recensuit, et Commentarius illustravit Johannes Gravius. Londini, J. Flesher. Latin and Persian on opposite pages. That part of the Zij dealing with chronology.

1652. John Greaves (1602-1652). Binae Tabulae Geographicae, una Nassir Eddini Persae, altera Vlug Beigi Tatari: Opera et Studio J. Gravii nunc primum publicatae. Londini, Typis Jacobi Flesher: prostant apud Cornelium Bee. 2nd edition of geographical tables.

1665. Thomas Hyde (1636-1703). Tabulae long. ac lat. stellarum fixarum, ex observatione Ulugh Beighi, Tamerlanis Magni Nepotis, Regionum ultra citraque Gjihun (i. Oxum) Principis potentissimi. Ex tribus invicem collatis MSS. Persicis jam primum Luce ac Latiodonavit, & commentariis illustravit, Thomas Hyde. In calce libriaccesserunt Mohammedis Tizini tabulae declinationum & rectarium ascensionum. Additur demum Elenchus Nominum Stellarum. Oxonii: Typis Henrici Hall, sumptibus authoris. Tables in Latin and Persian for 1018 stars of which about 700 were based exclusively on Ulugh Beg and the balance were reduced from Ptolemy in one or both coordinates. Hyde appears to have worked totally independent of Greaves.

1690. Johannes Hevelius (1611-1687). Prodromus Astronomiae. Danzig. Contains a comparison of data in Ulugh Beg's tables with other star catalogues known at that time -- those of Ptolemy, Tycho Brahe, Giambattista Riccioli, Wilhelm IV (Landgrave of Hesse-Cassel), and Hevelius.

1698-1712. Geographiae veteris scriptores graeci minores. Cum interpretatione latina, dissertationibus, ac annotationibus... Oxoniae, e Theatro Sheldoniano. A work containing Ulugh Beg's geographical tables.

1725. John Flamsteed (1646-1719). Historia Coelestis Britannica. London, 3 vols. Includes Ulugh Beg's catalogue, along with those of Ptolemy, Tycho Brahe, Wilhelm IV, and Hevelius.

1767. Gregory Sharpe. Syntagma dissertationum quas olim auctor doctissimus Thomas Hyde, S. T. P. separatim edidit. Accesserunt nonnulla ejusdem opuscula hactenus inedita, &c. &c. Omnia diligenter recognita a Gregorio Sharpe, LL.D. Reg. Maj. a sacris. Templi Magistro S.S.R. et A.S. Oxonii. Reprint, with corrections, of Hyde's 1665 work on the Zij, in a 2 vol. collection of Hyde's work.

1807. Duo pinakez geographikoi, d men Nassir 'Eddinou Persou, d de Ouloug Mpei Tatarou. 'Epimeleia kai opoudh Dhmhtriou 'Alexandridou ... Kata thn en 'Oxonia ekdosin tou sophou Grauiou. 'En Biennh thz Austriaz, ek thz tupographiaz 'A. Sxmidiou. Ulugh Beg's geographical tables published in Vienna in a Greek-language edition.

1843. Francis Baily (1774-1844). "The Catalogues of Ptolemy, Ulugh Beigh, Tycho Brahe, Halley and Hevelius, Deduced From the Best Authorities, With Various Notes and Corrections," Memoires of the Royal Astronomical Society 13, pp. 19-28, 79-125, London. Reprinted from Thomas Hyde's translation, as edited by Gregory Sharpe in 1767.

1839. L. P. E. A. Sedillot (1808-1875). Tables astronomiques d'Oloug Beg, commentees et publiees avec le texte en regard, TomeI, 1 fascicule, Paris. A very rare work, but referenced in the Bibliographie generale de l'astronomie jusqu'en 1880, by J. C. Houzeau and A. Lancaster (Brussels, 3 vols. 1887-9; reprinted London, 1964).

1847. L. P. E. A. Sedillot (1808-1875). Prolegomenes des Tables astronomiques d'Oloug Beg, publiees avec Notes et Variantes, et precedes d'une Introduction. Paris: F. Didot.

1853. L. P. E. A. Sedillot (1808-1875). Prolegomenes des Tables astronomiques d'Oloug Beg, traduction et commentaire. Paris.

1917. Edward Ball Knobel (1841-1930). Ulugh Beg's Catalogue of Stars, Revised from all Persian Manuscripts Existing in Great Britain, with a Vocabulary of Persian and Arabic Words. Washington, D. C.: The Carnegie Institute of Washington.