Introduction
Ulugh Beg (1394–1449) was a grandson of Timur, founder of the Timurid Empire. His given name was Mirza Muhammad Taraghay; "Ulugh Beg" is a nickname meaning "Great Ruler". He became governor of Samarkand in 1409 (at the age of 16) and ruler of the whole province known to the Romans as Transoxiana (roughly, modern day Uzbekistan) in 1411.
Ulugh Beg became interested in astronomy at a young age, after visiting the Maragheh observatory founded by the Persian scholar and astronomer Nasir al-Din al-Tusi (1201–1274). He turned Samarkand into an intellectual center, building a madrasa and inviting astronomers and mathematicians from the Islamic world. Between 1424 and 1429, he built an enormous observatory in Samarkand where the observations leading to his star catalog were conducted.
The end of Ulugh Beg's life was marked by civil wars of succession. He ended up being assassinated on the orders of his oldest son in 1449.
More biographical details can be found in Baily [3] in the introduction to Ulugh Beg's catalog. See also R. H. van Gent's pages on Ulugh Beg. This page focuses on Ulugh Beg's star catalog.
The star catalog
Ulugh Beg's star catalog is based on Abd al-Rahman al-Sufi's Book of the Constellations of the Fixed Stars [6], in a Persian translation made around 1250 by al-Tusi (see R. H. van Gent's page on al-Sufi). Al-Sufi's catalog has the same structure as Ptolemy's. The star positions are Ptolemy's, precessed in longitude by 12°42' to refer them to the equinox of year 1276 Alexander (Seleucid era), or 964 CE, or 353 AH (Knobel [2, p. 12]). The star magnitudes are based on al-Sufi's own observations.
Ulugh Beg and his assistants measured the positions of most al-Sufi's stars anew at the observatory of Samarkand between 1420 and 1437. The star catalog and its preface were published in 1437 under the title Zij-i Sultani (Zij Ulugh Beg according to Baily; alternative names are mentioned by Knobel [2, p. 5]). It was probably written in Persian and translated into Arabic (Knobel [3, pp. 5–6]). The equinox chosen for star positions is the beginning of hear 841 of the Hegira (Knobel [2, p. 9]), or 1437-07-05 (Julian) according to the tabular Islamic calendar.
The preface explains that all the stars from al-Sufi's catalog were reobserved, except 27 that are too far south to be visible at Samarkand (Ptolemy's Nav 36–41, Nav 44 & 45, Cen 27–37, Lup 10, Ara 1–7), and another 8 that could not be found by al-Sufi nor Ulugh Beg (Ptolemy's Aur 14, Lup 11, PsA~1–6) (Knobel [3, pp. 8–9]). Still according to the preface, the 27 southern stars have their positions taken from al-Sufi (and precessed according to the difference of equinox) and the 8 unidentified stars have been omitted. This statement seems to be inaccurate for Lup 11, present in Ulugh Beg's catalog with a position derived from Ptolemy, as well as Cen 30, mentioned without position, and maybe Nav 44 & 45 mentioned without position in some of the versions examined.
Ulugh Beg's catalog has therefore the same structure as Ptolemy's, covers the same constellations and almost the same stars. Ptolemy's 3 duplicate entries (Her 29, Tau 21, PsA 1) and 7 of the unidentified stars (Aur 14, PsA~1 to PsA~6) are omitted, as they were by al-Sufi, so that the catalog contains 1018 entries.
Editions of the catalog
In 1665, orientalist and librarian Thomas Hyde (1636–1703) published a Latin translation of Ulugh Beg's catalog (Hyde [5]) based on three manuscripts present in Oxford. A second edition of this translation was published by Dr. Gregory Sharpe in 1767 (Sharpe [4]) in a collected edition of Hyde's work. Sharpe's edtion of the catalog is included in Francis Baily's collection of ancient star catalogs (Baily [3]) published in 1843, including cross-references to Bayer's atlas, Flamsteed's and Lacaille's catalogs.
In 1931, Edward B. Knobel published a translation and analysis of Ulugh Beg's catalog, based on Persian and Arabic manuscripts available in England (Knobel [2]). He included cross-references in the form of Bayer, Flamsteed, Piazzi designations (not always in agreement with Baily's). This version has been put in machine-readable form by F. Verbunt and R. H. van Gent [1] as part of their study of Ptolemy's and Ulugh Beg's catalogs, and made available as VizieR's catalog J/A+A/544/A31.
This page presents machine-readable versions of Ulugh Beg's catalog according to Hyde, Sharpe, Baily and Knobel (the latter in full agreement with VizieR's). The star maps on the next page provide graphical representations of the catalog.
Catalog data
The following files cover catalog data.
| File name | Explanation |
|---|---|
| ReadMe | File descriptions |
| ulughbeg_h.dat | Ulugh Beg's catalog from Hyde |
| ulughbeg_s.dat | Ulugh Beg's catalog from Sharpe |
| ulughbeg_b.dat | Ulugh Beg's catalog from Baily |
| ulughbeg_k.dat | Ulugh Beg's catalog from Knobel |
| notes.dat | Notes on these versions of the catalog |
| pto2beg.dat | Mapping between Ptolemy's and Ulugh Beg's catalogs |
| names.dat | Arabic star names from Hyde and variants from Sharpe and Baily |
The ReadMe file describes the file formats, following the conventions for catalog descriptions of the VizieR service.
The catalog files include the star descriptions in Latin (Hyde, Sharpe, Baily) or French (Knobel), UTF-8 encoded, starting on column 34, that have to be stripped before VizieR's automatic validation can work.
The file pto2beg.dat establishes the correspondence between Ptolemy's and Ulugh Beg's catalogs, as a cursory examination suggests, and flags the cases where the star observed by Ulugh Beg may not be the same as the one intended by Ptolemy.
The file names.dat gathers all the Arabic star names from Hyde's version, in their Latin alphabet transliteration, and mentions alternative spellings and other differences from Sharpe's and Baily's. A dash means that no name is present and an asterisk means that the previous name applies to the current star.
Star identifications
Baily assigns Bayer, Flamsteed or, in the notes, Piazzi designations to Ulugh Beg's stars. Knobel uses Bayer, Flamsteed, Piazzi, or Hevelius designations.
These identifications are gathered in their raw form in the following files, described in ReadMe.
| File name | Explanation |
|---|---|
| cross_k.dat | Star identifications according to Knobel [2] |
| cross_b.dat | Star identifications according to Baily [3] |
Summary files
As aids to quickly compare different versions of the catalog, the files pos_all.dat and mag_all.dat collect the positions and magnitudes according to all versions in one place.
| File name | Explanation |
|---|---|
| pos_all.dat | Star positions across all versions |
| mag_all.dat | Star magnitudes across all versions |
References
[1] F. Verbunt and R. H. van Gent, The star catalogues of Ptolemaios and Ulugh Beg, Astronomy & Astrophysics, 455, A31 (2012).
[2] Edward Ball Knobel, Ulugh Beg's Catalogue of Stars, The Carnegie Institution of Washington, Washington, 1917.
[3] Francis Baily, The Catalogues of Ptolemy, Ulugh Beigh, Tycho Brahe, Halley, Hevelius, Deduced from the Best Authorities. With Various Notes and Corrections, and a Preface to Each Catalogue. To Which is Added the Synonym of each Star, in the Catalogues of Flamsteed or Lacaille, as far as the same can be ascertained. Memoirs of the Royal Astronomical Society, Vol. 13, London, 1843. Also available here.
[4] Gregorius Sharpe, Syntagma dissertationum quas olim dictissimus Thomas Hyde, S.T.P. separatim edidit. ..., Clarendon press, Oxford, 1767.
[5] Thomas Hyde, Tabulae Long. ac Lat. Stellarum Fixarum, ex Observatione Ulugh Beighi, …. Henry Hall, Oxford, 1665.
[6] Abd al-Rahman al-Sufi, Book of the Constellations of the Fixed Stars, Shira, 964. Available here. English translation by Ihsan Hafez (2010) included in his Ph.D. thesis available here. French translation by Hans Schjellerup (1874) available here.