Zij-i-Sultani
Encyclopedia
Zīj-i Sultānī is a Zij
astronomical table and star catalogue that was published by Ulugh Beg
in 1437. It was the joint product of the work of a group of Muslim astronomers working under the patronage of Ulugh Beg
at Samarkand
's Ulugh Beg Observatory
. These astronomers included Jamshīd al-Kāshī
and Ali Qushji, among others.
The Zij-i-Sultani is generally considered the most accurate and extensive star catalogue
until its time, surpassing its predecessors, including Ptolemy
's work, Abd al-Rahman al-Sufi's Book of Fixed Stars
, and the Maragheh observatory
's Zij-i Ilkhani
. It was not surpassed until the work of Taqi al-Din and Tycho Brahe
in the 16th century.
The serious errors which 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 Tabulae longitudinis et latitudinis stellarum fixarum ex observatione Ulugbeighi by G. 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
as 365.2570370...d = 365d 6h 10m 8s (an error +58s). In his measurements within many years he used a 50 m high gnomon
. This value was improved by 28s, 88 years later in 1525 by Nicolaus Copernicus
(1473-1543), who appealed to the estimation of Thabit ibn Qurra
(826
-901
), which was accurate to +2s. However, Beg later measured another more precise value as 365d 5h 49m 15s, which has an error of +25s, making it more accurate than Copernicus' estimate which had an error of +30s. Beg also determined the Earth's axial tilt
as 23.52 degrees, which remains the most accurate measurement to date. It was more accurate than later measurements by Copernicus and Tycho Brahe
, and matches the currently accepted value precisely.
Zij
Zīj is the generic name applied to Islamic astronomical books that tabulate parameters used for astronomical calculations of the positions of the Sun, Moon, stars, and planets. The name is derived from the Middle Persian term zih or zīg, meaning cord...
astronomical table and star catalogue that was published by Ulugh Beg
Ulugh Beg
Ulugh Bek was a Timurid ruler as well as an astronomer, mathematician and sultan. His commonly-known name is not truly a personal name, but rather a moniker, which can be loosely translated as "Great Ruler" or "Patriarch Ruler" and was the Turkic equivalent of Timur's Perso-Arabic title Amīr-e...
in 1437. It was the joint product of the work of a group of Muslim astronomers working under the patronage of Ulugh Beg
Ulugh Beg
Ulugh Bek was a Timurid ruler as well as an astronomer, mathematician and sultan. His commonly-known name is not truly a personal name, but rather a moniker, which can be loosely translated as "Great Ruler" or "Patriarch Ruler" and was the Turkic equivalent of Timur's Perso-Arabic title Amīr-e...
at Samarkand
Samarkand
Although a Persian-speaking region, it was not united politically with Iran most of the times between the disintegration of the Seleucid Empire and the Arab conquest . In the 6th century it was within the domain of the Turkic kingdom of the Göktürks.At the start of the 8th century Samarkand came...
's Ulugh Beg Observatory
Ulugh Beg Observatory
The Ulugh Beg Observatory is an observatory in Samarkand, Uzbekistan. Built in the 1420s by the Timurid astronomer Ulugh Beg, it is considered by scholars to have been one of the finest observatories in the Islamic world at the time and the largest in Central Asia before it was destroyed in 1449...
. These astronomers included Jamshīd al-Kāshī
Jamshid al-Kashi
Ghiyāth al-Dīn Jamshīd Masʾūd al-Kāshī was a Persian astronomer and mathematician.-Biography:...
and Ali Qushji, among others.
The Zij-i-Sultani is generally considered the most accurate and extensive star catalogue
Star catalogue
A star catalogue, or star catalog, 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, and this article covers only some...
until its time, surpassing its predecessors, including Ptolemy
Ptolemy
Claudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...
's work, Abd al-Rahman al-Sufi's Book of Fixed Stars
Book of Fixed Stars
The Book of Fixed Stars is an astronomical text written by Abd al-Rahman al-Sufi around 964. The book was written in Arabic, although the author himself was Persian...
, and the Maragheh observatory
Maragheh observatory
Maragheh observatory is an astronomical observatory which was established in 1259 CE by Nasir al-Din al-Tusi, an Iranian scientist and astronomer...
's Zij-i Ilkhani
Zij-i Ilkhani
Zīj-i Īlkhānī or Ilkhanic Tables is a Zij book with astronomical tables of planetary movements. It was compiled by the Persian astronomer Nasir al-Din al-Tusi in collaboration with his research team of astronomers at the Maragha observatory...
. It was not surpassed until the work of Taqi al-Din and Tycho Brahe
Tycho Brahe
Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...
in the 16th century.
The serious errors which Beg found in previous Zij
Zij
Zīj is the generic name applied to Islamic astronomical books that tabulate parameters used for astronomical calculations of the positions of the Sun, Moon, stars, and planets. The name is derived from the Middle Persian term zih or zīg, meaning cord...
star catalogues (many of the earlier ones were simply updates on Ptolemy's work, adding the effect of precession
Precession of the equinoxes
In astronomy, axial precession is a gravity-induced, slow and continuous change in the orientation of an astronomical body's rotational axis. In particular, it refers to the gradual shift in the orientation of Earth's axis of rotation, which, like a wobbling top, traces out a pair of cones joined...
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
Thomas Hyde
Thomas Hyde was an English orientalist. The first use of the word dualism is attributed to him, in 1700.-Life:He was born at Billingsley, near Bridgnorth in Shropshire, on 29 June 1636...
at Oxford in 1665 under the title Tabulae longitudinis et latitudinis stellarum fixarum ex observatione Ulugbeighi by G. Sharpe in 1767, and in 1843 by Francis Baily
Francis Baily
Francis Baily was an English astronomer, most famous for his observations of 'Baily's beads' during an eclipse of the Sun.-Life:Baily was born at Newbury in Berkshire in 1774...
in vol. xiii. of the Memoirs of the Royal Astronomical Society.
In 1437, Ulugh Beg determined the length of the sidereal year
Sidereal year
A sidereal year is the time taken by the Earth to orbit the Sun once with respect to the fixed stars. Hence it is also the time taken for the Sun to return to the same position with respect to the fixed stars after apparently travelling once around the ecliptic. It was equal to at noon 1 January...
as 365.2570370...d = 365d 6h 10m 8s (an error +58s). In his measurements within many years he used a 50 m high gnomon
Gnomon
The gnomon is the part of a sundial that casts the shadow. Gnomon is an ancient Greek word meaning "indicator", "one who discerns," or "that which reveals."It has come to be used for a variety of purposes in mathematics and other fields....
. This value was improved by 28s, 88 years later in 1525 by Nicolaus Copernicus
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....
(1473-1543), who appealed to the estimation of Thabit ibn Qurra
Thabit ibn Qurra
' was a mathematician, physician, astronomer and translator of the Islamic Golden Age.Ibn Qurra made important discoveries in algebra, geometry and astronomy...
(826
826
Year 826 was a common year starting on Monday of the Julian calendar.- Religion :* June 24 – The Danish king Harald Klak accepts Christianity.- Deaths :...
-901
901
Year 901 was a common year starting on Thursday of the Julian calendar.- Africa :* Abu 'Abdullah al-Shi'i leads the rebellion of the Kutama Berbers against the Aghlabid emirate in Ifriqiya ....
), which was accurate to +2s. However, Beg later measured another more precise value as 365d 5h 49m 15s, which has an error of +25s, making it more accurate than Copernicus' estimate which had an error of +30s. Beg also determined the Earth's axial tilt
Axial tilt
In astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...
as 23.52 degrees, which remains the most accurate measurement to date. It was more accurate than later measurements by Copernicus and Tycho Brahe
Tycho Brahe
Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...
, and matches the currently accepted value precisely.