Islamic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age (9th–13th centuries), and mostly written in the Arabic language.

These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and later in the Far East and India.

It closely parallels the genesis of other Islamic sciences in its assimilation of foreign material and the amalgamation of the disparate elements of that material to create a science with Islamic characteristics. These included Greek, Sassanid, and Indian works in particular, which were translated and built upon.

Islamic astronomy played a significant role in the revival of Byzantine and European astronomy following the loss of knowledge during the early medieval period, notably with the production of Latin translations of Arabic works during the 12th century. Islamic astronomy also had an influence on Chinese astronomy and Malian astronomy.

A significant number of stars in the sky, such as Aldebaran, Altair and Deneb, and astronomical terms such as alidade, azimuth, and nadir, are still referred to by their Arabic names.

A large corpus of literature from Islamic astronomy remains today, numbering approximately 10,000 manuscripts scattered throughout the world, many of which have not been read or cataloged. Even so, a reasonably accurate picture of Islamic activity in the field of astronomy can be reconstructed.

History

Ahmad Dallal notes that, unlike the Babylonians, Greeks, and Indians, who had developed elaborate systems of mathematical astronomical study, the pre-Islamic Arabs relied entirely on empirical observations.

These observations were based on the rising and setting of particular stars, and this area of astronomical study was known as anwa. Anwa continued to be developed after Islamization by the Arabs, where Islamic astronomers added mathematical methods to their empirical observations.

According to David King, after the rise of Islam, the religious obligation to determine the qibla and prayer times inspired more progress in astronomy for centuries.

Donald Hill (1993) divided Islamic Astronomy into the four following distinct time periods in its history:

1. Early Islam

Following the Islamic conquests, under the early caliphate, Muslim scholars began to absorb Hellenistic and Indian astronomical knowledge via translations into Arabic (in some cases via Persian).

The first astronomical texts that were translated into Arabic were of Indian and Persian origin. The most notable of the texts was Zij al-Sindhind an 8th-century Indian astronomical work that was translated by Muhammad ibn Ibrahim al-Fazari and Yaqub ibn Tariq after 770 CE with the assistance of Indian astronomers who visited the court of caliph Al-Mansur in 770.

Another text translated was the Zij al-Shah, a collection of astronomical tables (based on Indian parameters) compiled in Sasanid Persia over two centuries.

Fragments of texts during this period indicate that Arabs adopted the sine function (inherited from India) in place of the chords of arc used in Greek trigonometry.

Golden Age

The House of Wisdom was an academy established in Baghdad under Abbasid caliph Al-Ma’mun in the early 9th century.

From this time, independent investigation into the Ptolemaic system became possible. According to Dallal (2010), the use of parameters, sources and calculation methods from different scientific traditions made the Ptolemaic tradition “receptive right from the beginning to the possibility of observational refinement and mathematical restructuring“.

Astronomical research was greatly supported by the Abbasid caliph al-Mamun through the House of Wisdom. Baghdad and Damascus became the centers of such activity. The caliphs not only supported this work financially but endowed the work with formal prestige.

The first major Muslim work of astronomy was Zij al-Sindh by al-Khwarizmi in 830. The work contains tables for the movements of the Sun, the Moon and the five planets known at the time.

The work is significant as it introduced Ptolemaic concepts into Islamic sciences. This work also marks the turning point in Islamic astronomy.

Hitherto, Muslim astronomers had adopted a primary research approach to the field, translating works of others and learning already discovered knowledge. Al-Khwarizmi’s work marked the beginning of nontraditional methods of study and calculations.

In 850, al-Farghani wrote Kitab fi Jawani (meaning “A compendium of the science of stars”). The book primarily gave a summary of Ptolemic cosmography.

However, it also corrected Ptolemy based on findings of earlier Arab astronomers. Al-Farghani gave revised values for the obliquity of the ecliptic, the precessional movement of the apogees of the Sun and the Moon, and the circumference of the Earth. The book was widely circulated through the Muslim world, and translated into Latin.

Egyptian astronomer Ibn Yunus was actually the first astronomer to really find valid fault in Ptolemy’s calculations about the planet’s movements and their peculiarity in the late 10th century.

Ptolemy calculated that Earth’s wobble, otherwise known as precession, varied 1 degree every 100 years. Ibn Yunus contradicted this finding by calculating that it was instead 1 degree every 70​1⁄4 years. Ibn Yunus and Ibn al-Shatir’s findings were part of Copernicus’s calculations to figure out that the Sun was the center of the universe.

The period when a distinctive Islamic system of astronomy flourished. The period began as the Muslim astronomers began questioning the framework of the Ptolemaic system of astronomy.

These criticisms, however, remained within the geocentric framework and followed Ptolemy’s astronomical paradigm; one historian described their work as “a reformist project intended to consolidate Ptolemaic astronomy by bringing it into line with its own principles.

Between 1025 and 1028, Ibn al-Haytham wrote his Al-Shukuk ala Batlamyus (meaning “Doubts on Ptolemy”). While maintaining the physical reality of the geocentric model, he criticized elements of the Ptolemic models.

Many astronomers took up the challenge posed in this work, namely to develop alternate models that resolved these difficulties. In 1070, Abu Ubayd al-Juzjani published the Tarik al-Aflak where he discussed the “equant” problem of the Ptolemic model and proposed a solution.

In Al-Andalus, the anonymous work al-Istidrak ala Batlamyus (meaning “Recapitulation regarding Ptolemy”), included a list of objections to the Ptolemic astronomy.

Later period

Notable astronomers from the later medieval period include Mu’ayyad al-Din al-‘Urdi (c. 1266), Nasir al-Din al-Tusi (1201–74), Qutb al-Din al Shirazi (c. 1311), Sadr al-Sharia al-Bukhari (c. 1347), Ibn al-Shatir (c. 1375), and Ali al-Qushji (c. 1474).

In the fifteenth century, the Timurid ruler Ulugh Beg of Samarkand established his court as a center of patronage for astronomy.

He studied it in his youth, and in 1420 ordered the construction of Ulugh Beg Observatory, which produced a new set of astronomical tables, as well as contributing to other scientific and mathematical advances.

Influences in East Asia

Islamic influence on Chinese astronomy was first recorded during the Song dynasty when a Hui Muslim astronomer named Ma Yize introduced the concept of seven days in a week and made other contributions.

Islamic astronomers were brought to China in order to work on calendar making and astronomy during the Mongol Empire and the succeeding Yuan Dynasty.

The Chinese scholar Yeh-lu Chu’tsai accompanied Genghis Khan to Persia in 1210 and studied their calendar for use in the Mongol Empire. Kublai Khan brought Iranians to Beijing to construct an observatory and an institution for astronomical studies.

Several Chinese astronomers worked at the Maragheh observatory, founded by Nasir al-Din al-Tusi in 1259 under the patronage of Hulagu Khan in Persia.

One of these Chinese astronomers was Fu Mengchi or Fu Mezhai. In 1267, the Persian astronomer Jamal ad-Din, who previously worked at Maragha observatory, presented Kublai Khan with seven Persian astronomical instruments, including a terrestrial globe and an armillary sphere, as well as an astronomical almanac, which was later known in China as the Wannian Li (“Ten Thousand Year Calendar” or “Eternal Calendar”).

He was known as “Zhamaluding” in China, where, in 1271, he was appointed by Khan as the first director of the Islamic observatory in Beijing, known as the Islamic Astronomical Bureau, which operated alongside the Chinese Astronomical Bureau for four centuries.

Islamic astronomy gained a good reputation in China for its theory of planetary latitudes, which did not exist in Chinese astronomy at the time, and for its accurate prediction of eclipses.

Instruments

Our knowledge of the instruments used by Muslim astronomers primarily comes from two sources: first the remaining instruments in private and museum collections today, and second the treatises and manuscripts preserved from the Middle Ages.

Muslim astronomers of the “Golden Period” made many improvements to instruments already in use before their time, such as adding new scales or details.

Celestial globes and armillary spheres

Celestial globes were used primarily for solving problems in celestial astronomy. Today, 126 such instruments remain worldwide, the oldest from the 11th century.

The altitude of the Sun or the Right Ascension and Declination of stars could be calculated with these by inputting the location of the observer on the meridian ring of the globe.

An armillary sphere had similar applications. No early Islamic armillary spheres survive, but several treatises on “the instrument with the rings” were written.

In this context, there is also an Islamic development, the spherical astrolabe, of which only one complete instrument, from the 14th century, has survived.

Astrolabes

Brass astrolabes were a Hellenistic invention. The first Islamic astronomer reported as having built an astrolabe is Muhammad al-Fazari (late 8th century).

Astrolabes were popular in the Islamic world during the “Golden Age“, chiefly as an aid to finding the qibla. The earliest known example is dated to 927/8 (AH 315).

The instruments were used to read the time of rising of the Sun and fixed stars. al-Zarqali of Andalusia constructed one such instrument in which, unlike its predecessors, did not depend on the latitude of the observer, and could be used anywhere. This instrument became known in Europe as the Saphea.

Mechanical calendar

Abu Rayhan Biruni made an instrument he called “Box of the Moon“, which was a mechanical lunisolar calendar, employing a gear train and eight gear-wheels. This was an early example of a fixed-wired knowledge processing machine.

Sundials

Muslims made several important improvements to the theory and construction of sundials, which they inherited from their Indian and Greek predecessors. Khwarizmi made tables for these instruments which considerably shortened the time needed to make specific calculations.

Sundials were frequently placed on mosques to determine the time of prayer. One of the most striking examples was built in the fourteenth century by the muwaqqit (timekeeper) of the Umayyad Mosque in Damascus, ibn al-Shatir.

Quadrants

Several forms of quadrants were invented by Muslims. Among them was the sine quadrant used for astronomical calculations, and various forms of the horary quadrant used to determine the time (especially the times of prayer) by observations of the Sun or stars. A center of the development of quadrants was ninth-century Baghdad.

Equatoriums

The Equatorium is an invention from Al-Andalus, by Al-Zarqali. The earliest known was made in the eleventh century.

It is a mechanical device for finding the positions of the moon, sun, stars, and planets, without calculation using a geometrical model to represent the celestial body’s mean and anomalistic position.

*This article was originally published at en.wikipedia.org.