''Zīj-i Sulṭānī'' ( fa, زیجِ سلطانی) is a Zij astronomical table and

star catalogue A star catalogue is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years ...

that was published by Ulugh Beg in 1438–1439. It was the joint product of the work of a group of Muslim astronomers working under the patronage of Ulugh Beg at

Samarkand fa, سمرقند , native_name_lang = , settlement_type = City , image_skyline = , image_caption = Clockwise from the top:Registan square, Shah-i-Zinda necropolis, Bibi-Khanym Mosque, view inside Shah-i-Zinda, ...

Ulugh Beg Observatory The Ulugh Beg Observatory is an observatory in Samarkand, Uzbekistan. Built in the 1420s by the Timurid astronomer Ulugh Beg. Islamic astronomers who worked at the observatory include Al-Kashi, Ali Qushji, and Ulugh Beg himself. The observa ...

. These astronomers included Jamshīd al-Kāshī and Ali Qushji, among others. The ''Zij-i-Sultani'' was not surpassed in accuracy until the work of Taqi al-Din and Tycho Brahe in the 16th century. The serious errors which Ulugh Beg found in previous Zij star catalogues (many of the earlier ones were simply updates on Ptolemy's work, adding the effect of precession to the longitudes) induced him to redetermine the positions of 992 fixed stars, to which he added 27 stars from al-Sufi's ''Book of Fixed Stars'' (964), which were too far south for observation from Samarkand. This catalogue, one of the most original of the Middle Ages, was edited by Thomas Hyde at Oxford in 1665 under the title ''Jadāvil-i Mavāzi' S̱avābit, sive, Tabulae Long. ac Lat. Stellarum Fixarum ex Observatione Ulugh Beighi'', by Gregory Sharpe in 1767, and in 1843 by Francis Baily in Vol. XIII of the ''Memoirs of the Royal Astronomical Society''. In 1437, Ulugh Beg determined the length of the

sidereal year A sidereal year (, ; ), also called a sidereal orbital period, is the time that Earth or another planetary body takes to orbit the Sun once with respect to the fixed stars. Hence, for Earth, it is also the time taken for the Sun to return to t ...

as 365.2570370...^d = 365^d 6^h 10^m 8^s (an error of +58^s). In his measurements over many years he used a 50 m high

gnomon A gnomon (; ) is the part of a sundial that casts a shadow. The term is used for a variety of purposes in mathematics and other fields. History A painted stick dating from 2300 BC that was excavated at the astronomical site of Taosi is the ...

. This value was improved by 28^s, 88 years later in 1525 by

Nicolaus Copernicus Nicolaus Copernicus (; pl, Mikołaj Kopernik; gml, Niklas Koppernigk, german: Nikolaus Kopernikus; 19 February 1473 – 24 May 1543) was a Renaissance polymath, active as a mathematician, astronomer, and Catholic canon, who formulat ...

(1473–1543), who appealed to the estimation of Thabit ibn Qurra (826–901), which was accurate to +2^s. However, Ulugh Beg later measured another more precise value as 365^d 6^h 9^m 35^s, which has an error of +25^s, making it more accurate than Copernicus' estimate which had an error of +30^s. Ulugh Beg also determined the Earth's

axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orb ...

as 23;30,17 degrees in

sexagesimal Sexagesimal, also known as base 60 or sexagenary, is a numeral system with sixty as its base. It originated with the ancient Sumerians in the 3rd millennium BC, was passed down to the ancient Babylonians, and is still used—in a modified form ...

notation, which in decimal notation converts to 23.5047 degrees.L.P.E.A. Sédillot, ''Prolégomènes des tables astronomiques d'OlougBeg: Traduction et commentaire'' (Paris: Firmin Didot Frères, 1853), pp.&nbs
87

253

Notes

References

* E.S. Kennedy, ''A Survey of Islamic Astronomical Tables'', Transactions of the American Philosophical Society, (1956) 46(2), pp. 3–4, 44-5. * L.P.E.A. Sédillot. Tables astronomiques d’Oloug Beg, commentées et publiées avec le texte en regard, Tome I, 1 fascicule, Paris; 1839. * L.P.E.A. Sédillot. Prolégomènes des Tables astronomiques d’Oloug Beg, publiées avec Notes et Variantes, et précédées d’une Introduction. Paris: F. Didot, 1847. * L.P.E.A. Sédillot. Prolégomènes des Tables astronomiques d’Oloug Beg, traduction et commentaire. Paris: 1853. {{Authority control 1437 books Astronomical tables Astronomical works of the medieval Islamic world Astrological works of the medieval Islamic world

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References