Astronomy in the medieval Islamic world

This is a sub-article of History of science in the Islamic World and Astronomy.

In the history of astronomy, Islamic astronomy or Arabic astronomy refers to the astronomical developments made by the Islamic civilisation between the 8th and 15th centuries. 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 that was essentially Islamic. These include Indian and Sassanid works in particular. Some Hellenistic texts were also translated and built upon as well.

Some stars in the sky, such as Aldebaran, are still today recognized with their Arabic names.

History

Pre-Islamic Arabs had no scientific astronomy. Their knowledge of stars was only empirical, limited to what they observed regarding the rising and setting of stars. The rise of Islam provoked increased Arab thought in this field.

Science historian Donald Routledge Hill has divided Islamic Astronomy into the four following distinct time periods in its history.

700-825

The period of assimilation and syncretisation of earlier Hellenistic, Indian and Sassanid astronomy.

During this period, a number of Sanskrit and Persian texts were translated into Arabic. The most notable of the texts was Zij al-Sindhind, translated by Muhammad al-Fazari and Yaqūb ibn Tāriq in 777. Sources indicate that the text was translated after, in 770, an Indian astronomer visited the court of Caliph Al-Mansur. Another text translated was the Zij al-Shah, a collection of astronomical tables compiled in Persia over two centuries.

Fragments of text during this period indicate that Arabs adopted the sine function (inherited from Indian trigonometry) instead of the chords of arc used in Hellenistic mathematics.

825-1025

This period of vigorous investigation, in which the superiority of the Ptolemaic system of astronomy was accepted and significant contributions made to it. Astronomical research was greatly supported by the Abbasid caliph al-Mamun. 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-Khwarizimi 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 primarily 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 ("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 books were widely circulated through the Muslim world, and even translated into Latin.

1025-1450

File:Ibn haithem portrait.jpg

Ibn al-Haytham (Alhacen) was a pioneer of the Muslim haya tradition of astronomy and laid the theoretical foundations for modern telescopic astronomy.

During this period a distinctive Islamic system of astronomy flourished. Within the Greek tradition and its successors it was traditional to separate mathematical astronomy (as typified by Ptolemy) from philosophical cosmology (as typified by Aristotle). Muslim scholars developed a program of seeking a physically real configuration (hay'a) of the universe, that would be consistent with both mathematical and physical principles. Within the context of this hay'a tradition, Muslim astronomers began questioning technical details of the Ptolemaic system of astronomy. This criticism remained within the geocentric framework and followed Ptolemy's astronomical paradigm. As the historian of astronomy, A. I. Sabra, noted:

"All Islamic astronomers from Thabit ibn Qurra in the ninth century to Ibn al-Shatir in the fourteenth, and all natural philosophers from al-Kindi to Averroes and later, are known to have accepted what Kuhn has called the "two-sphere universe" ...--the Greek picture of the world as consisting of two spheres of which one, the celestial sphere made up of a special element called aether, concentrically envelops the other, where the four elements of earth, water, air, and fire reside."

Some Muslim scholars, including al-Biruni, discussed whether the Earth moved and considered how this might be consistent with astronomical computations and physical systems. Several Muslim astronomers, most notably al-Tusi and his succesors, developed computational models that within a geocentric context that were later adapted in the Copernican model in a heliocentric context.

Ibn al-Haytham (Alhacen in Latin) in the early 11th century, while maintaining the physical reality of the geocentric system, criticized Ptolemy's astronomical system in his Al-Shuku ala Batlamyus (Doubts on Ptolemy) for relating actual physical motions to imaginary mathematical points, lines, and circles:

"Ptolemy assumed an arrangement that cannot exist, and the fact that this arrangement produces in his imagination the motions that belong to the planets does not free him from the error he committed in his assumed arrangement, for the existing motions of the planets cannot be the result of an arrangement that is impossible to exist."

He developed a physical structure of the Ptolemaic system in his Treatise on the configuration of the World, or Maqâlah fî hay'at al-‛âlam, which became an influential work in the hay'a tradition. The foundations of telescopic astronomy can also be traced back to Ibn al-Haytham, since his optical studies were influential in the later development of the modern telescope.

File:Abu-Rayhan Biruni 1973 Afghanistan post stamp.jpg

Al-Biruni introduced the analysis of the acceleration of planets, discovered that the motions of the solar apogee and precession are not identical, and suggested that the Earth's rotation on its axis would be consistent with his astronomical parameters.

In 1030, Abu al-Rayhan al-Biruni discussed the Indian theories of Aryabhata, Brahmagupta and Varahamihira in his Ta'rikh al-Hind (Latinized as Indica). Biruni stated that Brahmagupta and others consider that the earth rotates on the axis and Biruni noted that this does not create any mathematical problems.

In 1031, al-Biruni completed his extensive astronomical encyclopaedia Kitab al-Qanun al-Mas'udi (Latinized as Canon Mas’udicus), in which he recorded his astronomical findings and formulated astronomical tables. In it he presented a geocentric model, tabulating the distance of all the celestial spheres from the central Earth, computed according to the principles of Ptolemy's Almagest. The book introduces the mathematical technique of analysing the acceleration of the planets, and first states that the the motions of the solar apogee and the precession are not identical. Al-Biruni also discovered that the distance between the Earth and the Sun is larger than Ptolemy's estimate, on the basis that Ptolemy disregarded the annual solar eclipses. Al-Biruni also described the Earth's gravitation as:

"The attraction of all things towards the centre of the earth."

Abu Said Sinjari, a contemporary of Biruni, also suggested the possible heliocentric movement of the Earth around the Sun, which Biruni did not reject. Although al-Biruni was one of the first astronomers to suggest the Earth's rotation about its own axis, it is not clear whether he supported a geocentric or heliocentric model. He remarked that if the Earth rotates on its axis and moves around the Sun, it would remain consistent with his astronomical parameters:

"Rotation of the earth would in no way invalidate astronomical calculations, for all the astronomical data are as explicable in terms of the one theory as of the other. The problem is thus difficult of solution."

In 1070, Abu Ubayd al-Juzjani published the Tarik al-Aflak. In his work, he indicated the so-called "equant" problem of the Ptolemic model. Al-Juzjani even proposed a solution for the problem. In al-Andalus, the anonymous work al-Istidrak ala Batlamyus (meaning "Recapitulation regarding Ptolemy"), included a list of objections to the Ptolemic astronomy.

In 1121, Al-Khazini, in his treatise The Book of the Balance of Wisdom, states:

"For each heavy body of a known weight positioned at a certain distance from the centre of the universe, its gravity depends on the remoteness from the centre of the universe. For that reason, the gravities of bodies relate as their distances from the centre of the universe."

Al-Khazini was thus the first to propose the theory that the gravities of bodies vary depending on their distances from the centre of the Earth. This phenomenon was not proven until Newton's law of universal gravitation in the 18th century.

From the 13th century, many astronomers took up the challenge earlier posed by Ibn al-Haytham, namely to develop alternate models that evaded the errors found in the Ptolemaic model. The most important of these astronomers include: Mo'ayyeduddin Urdi (d. 1266), Nasir al-Din al-Tusi (1201-1274), 'Umar al-Katibi al-Qazwini (d. 1277), Qutb al-Din al-Shirazi (1236-1311), Sadr al-Sharia al-Bukhari (c. 1347), Ibn al-Shatir (1304-1375), and Ala al-Qushji (c. 1474).

File:Al-Tusi Nasir.jpeg

Nasir al-Din al-Tusi resolved significant problems in the Ptolemaic system with the Tusi-couple, which later played an important role in the Copernican model.

Nasir al-Din al-Tusi (1201-1274) resolved significant problems in the Ptolemaic system by developing the Tusi-couple as an alternative to the physically problematic equant introduced by Ptolemy, and conceived a plausible model for elliptical orbits. Tusi's student Qutb al-Din al-Shirazi (1236-1311), in his The Limit of Accomplishment concerning Knowledge of the Heavens, discusses the possiblity of heliocentrism. 'Umar al-Katibi al-Qazwini (d. 1277), who also worked at the Maraghah observatory, in his Hikmat al-'Ain, wrote an argument for a heliocentric model, though he later abandoned the idea.

Ibn al-Shatir (1304–1375), in his A Final Inquiry Concerning the Rectification of Planetary Theory, eliminated the need for an equant by introducing an extra epicycle, departing from the Ptolemaic system in a way very similar to what Copernicus later also did. Ibn al-Shatir proposed a system that was only approximately geocentric, rather than exactly so, having demonstrated trigonometrically that the Earth was not the exact center of the universe.

Y. M. Faruqi wrote:

"Ibn al-Shatir’s theory of lunar motion was very similar to that attributed to Copernicus some 150 years later".

"Whereas Ibn al-Shatir’s concept of planetary motion was conceived in order to play an important role in an earth-centred planetary model, Copernicus used the same concept of motion to present his sun-centred planetary model. Thus the development of alternative models took place that permitted an empirical testing of the models."

Ibn al-Shatir’s rectification was later used in the Copernican model, along with the earlier Tusi-couple of Nasir al-Din al-Tusi and the Urdi lemma of Mo'ayyeduddin Urdi (d. 1266). Their theorems played an important role in the Copernican model of heliocentrism, which Copernicus achieved by making the physical transformation that the Sun is fixed and not moving and the mathematical transformation of reversing the direction of the last vector connecting the Earth to the Sun. In the published version of his masterwork, Copernicus also cites the theories of Al-Battani, Arzachel (Al-Zarkali) and Averroes as influences, while the works of Ibn al-Haytham (Alhacen) and Abu al-Rayhan al-Biruni was also known in Europe at the time.

1450-1900

The period of stagnation, when the traditional system of astronomy continued to be practised with enthusiasm, but with rapidly decreasing innovation of any major significance.

A large corpus of literature from Islamic astronomy remains today, numbering around some 10,000 manuscript volumes scattered throughout the world. Much of which has not even been catalogued. Even so, a reasonably accurate picture of Islamic activity in the field of astronomy can be reconstructed.

Azophi's The Depiction of Celestial Constellations. The constellation pictured here is Sagittarius.

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Ulugh Beg, founder of a large Islamic observatory, honoured on this Soviet stamp.

Medieval manuscript by Qotbeddin Shirazi depicting an epicyclic planetary model.

Observatories

The first systematic observations in Islam are reported to have taken place under the patronage of al-Mamun. Here, and in many other private observatories from Damascus to Baghdad, meridian degrees were measured, solar parameters were established, and detailed observations of the Sun, Moon, and planets were undertaken.

In the 10th century, the Buwayhid dynasty encouraged the undertaking of extensive works in Astronomy, such as the construction of a large scale instrument with which observations were made in the year 950CE. We know of this by recordings made in the zij of astronomers such as Ibn al-Alam. The great astronomer Abd Al-Rahman Al Sufi was patronised by prince Adud o-dowleh, who systematically revised Ptolemy's catalogue of stars. Sharaf al-Daula also established a similar observatory in Baghdad. And reports by Ibn Yunus and al-Zarqall in Toledo and Cordoba indicate the use of sophisticated instruments for their time.

It was Malik Shah I who established the first large observatory, probably in Isfahan. It was here where Omar Khayyám with many other collaborators constructed a zij and formulated the Persian Solar Calendar a.k.a. the jalali calendar. A modern version of this calendar is still in official use in Iran today.

The most influential observatory was however founded by Hulegu Khan during the 13th century. Here, Nasir al-Din al-Tusi supervised its technical construction at Maragha. The facility contained resting quarters for Hulagu Khan, as well as a library and mosque. Some of the top astronomers of the day gathered there, and from their collaboration resulted important modifications to the Ptolemaic system over a period of 50 years.

In 1420, prince Ulugh Beg, himself an astronomer and mathematician, founded another large observatory in Samarkand, the remains of which were excavated in 1908 by Russian teams.

And finally, Taqi al-din bin Ma'ruf founded a large observatory in Istanbul in 1575, which was on the same scale as those in Maragha and Samarkand.

In modern times, Turkey [1][2]has many well equipped observatories, while Jordan [3], Palestine [4], Lebanon [5], UAE [6], Tunisia [7], and other Arab states are also active as well. Iran has modern facilities at Shiraz University and Tabriz University. In Dec 2005, Physics Today reported of Iranian plans to construct a "world class" facility with a 2.0 m telescope observatory in the near future.[8]

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.

Muslims made many improvements to instruments already in use before their time, such as adding new scales or details. Their contributions to astronomical instrumentation are abundant.

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

An 18th century Persian Astrolabe, kept at The Whipple Museum of the History of Science in Cambridge, England.

Brass astrolabes were developed in much of the Islamic world, chiefly as an aid to finding the qibla. The earliest known example is dated 315 (in the Islamic calendar, corresponding to 927-8CE). The first person credited for building the Astrolabe in the Islamic world is reportedly Fazari (Richard Nelson Frye: Golden Age of Persia. p163). He only improved it though, the Greeks had already invented astrolabes to chart the stars. The Arabs then took it during the Abbasid Dynasty and perfected it to be used to find the beginning of Ramadan, the hours of prayer, and the direction of Mecca.

The instruments were used to read the rise of the time of rise of the Sun and fixed stars. al-Zarqall 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 Saphaea.

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 14th century by the muwaqqit (timekeeper) of the Umayyid 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 time (especially the times of prayer) by observations of the Sun or stars. A center of the development of quadrants was ninth-century Baghdad.

Equatorium

The Equatorium is an Islamic invention from Andalusia. The earliest known was probably made around 1015 CE. It is a mechanical device for finding the positions of the Moon, Sun, and planets, without calculation using a geometrical model to represent the celestial body's mean and anomalistic position.

Muslim astronomers

Main article: Muslim astronomers

Famous Muslim astronomy books

• al-Khwarizmi (c. 830), Zij al-Sindhind
• al-Farghani (d. c. 850), Kitab fi Jawami Ilm al-Nujum

See also

• Islamic science
• Islamic Golden Age
• List of Muslim scientists
• List of Iranian scientists
• Islamic astrology
• Arab and Persian astrology
• Islam
• History of astronomy
• Hebrew astronomy
• Zij

References

• Abdulhak Adnan, La science chez les Turcs ottomans, Paris, 1939.
• K. Ajram (1992). Miracle of Islamic Science, Appendix B. Knowledge House Publishers. ISBN 0911119434.
• A. Baker and L. Chapter (2002), "Part 4: The Sciences". In M. M. Sharif, "A History of Muslim Philosophy", Philosophia Islamica.
• Richard Covington (May-June 2007). "Rediscovering Arabic science", Saudi Aramco World, p. 2-16.
• Ahmad Dallal, "Science, Medicine and Technology.", in The Oxford History of Islam, ed. John Esposito, New York: Oxford University Press, (1999).
• Antoine Gautier, L'âge d'or de l'astronomie ottomane, in L'Astronomie, (Monthly magazine created by Camille Flammarion in 1882), december 2005, volume 119.
• M. Gill (2005). Was Muslim Astronomy the Harbinger of Copernicanism?
• Donald R. Hill, Islamic Science And Engineering, Edinburgh University Press (1993), ISBN 0-7486-0455-3
• E. S. Kennedy, "A Survey of Islamic Astronomical Tables," Transactions of the American Philosophical Society, 46, 2 (1956).
• Edward S. Kennedy (1998), Astronomy and Astrology in the Medieval Islamic World. Brookfield, VT: Ashgate.
• David A. King (1986). Islamic mathematical astronomy. London.
• David A. King, "Islamic Astronomy", in Astronomy before the telescope, ed. Christopher Walker. British Museum Press, (1999), pp. 143-174. ISBN 0-7141-2733-7
• Seyyed H. Nasr, (1964) An Introduction to Islamic Cosmological Doctrines,, Cambridge: Belknap Press of the Harvard University Press.
• A. I. Sabra (1998). "Configuring the Universe: Aporetic, Problem Solving, and Kinematic Modeling as Themes of Arabic Astronomy," Perspectives on Science 6, p. 288-330.
• George Saliba (1999). Whose Science is Arabic Science in Renaissance Europe? Columbia University.
• George Saliba (2000). "Arabic versus Greek Astronomy: A Debate over the Foundations of Science", Perspectives on Science 8, p. 328-41.
• H. Suter (1902). Mathematiker und Astronomen der Araber.
• Dick Teresi, Jamil Ragep, and Roger Hart (2002). "Ancient Roots of Modern Science", Talk of the Nation (NPR discussion of intercultural scientific contacts; astronomy is discussed in the first fifteen-minute segment).

External links

• "Tubitak Turkish National Observatory Antalya"
• "Scientific American" article on Islamic Astronomy
• The Arab Union for Astronomy and Space Sciences (AUASS)
• King Abdul Aziz Observatory
• History of Islamic Astrolabes
• Arabic models for replacing the equant for the outer planets and Venus
• Ibn ash-Shatir model for Mercury
• Ibn ash-Shatir model for the Moon
• Arabian astronomy