Astronomy in the medieval Islamic world

This is a sub-article of Science in the Muslim world and Astronomy.

In its origins and development, Islamic astronomy 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 reagrding 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 India) in place of the chords of arc used in Greek trignometry.

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 (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 books was widely circulated through the Muslim world, and even translated into Latin.

1025-1450

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. Several Muslim scholars had discussions on whether the Earth moved and tried to explain how this might be possible, some of whom also considered the heliocentric possibility of the sun being the center of the solar system and the orbits of the planets being elliptical. Most of the criticisms directed towards Ptolemy, however, remained within the geocentric framework and followed Ptolemy's astronomical paradigm. A. I. Sabra described their work as:

"A reformist project intended to consolidate Ptolemaic astronomy by bringing it into line with its own principles."

In 1031, Abu-Rayhan Biruni in his Kitab al-qanun al-Mas’udi (Canon Mas’udicus in Latin), Biruni observed that the planets revolved in elliptical orbits, instead of the circular orbits of the Greeks. Abu Said Sinjari, a contemporary of Biruni, also suggested the possible heliocentric movement of the Earth around the Sun, which Biruni did not reject.

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.

Ibn al-Haytham (Alhacen) in the 12th century wrote a scathing critique of Ptolemy's model:

"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."

One of the most important works in the period was Al-Shuku ala Batlamyus ("Doubts on Ptolemy"). In this, the author summed up the inconsistencies of the Ptolemic models. Many astronomers took up the challenge posed in this work, namely to develop alternate models that evaded such errors. 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).

Nasir al-Din 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 rejected 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. His rectification was later used in the Copernican model, along with the earlier Tusi-couple and the Urdi lemma of Mo'ayyeduddin Urdi (d. 1266). Their theorems played an important role in the Copernican model of heliocentrism. In the published version of his masterwork, Copernicus also briefly discusses the theories of Al-Battani and Averroes.

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.

Celestial passages in the Qur'an

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

Some Muslims quote verses from the Qur'an that show God encourages people to engage in astronomy, in order to affirm the existence of God.

Regarding astronomy:

• Sura 3.190

In the creation of the heavens and the earth and in the alternation of the night and the day there are indeed Signs for men of understanding.;

• Sura 67.3-4

Who has created seven heavens in harmony. No incongruity canst thou see in the creation of the Gracious God. Then look again. Seest thou any flaw?

Regarding Physical cosmology:

• Sura 21.30

Do not the disbelievers see that the heavens and the earth were a closed up-mass, then WE opened them out? And WE made of water every living thing. Will they not then believe?

• Sura 41.11

Then HE turned to the heaven, while it was something like smoke, and said to it and to the earth; `Come ye both of you in obedience, willingly or unwillingly.' They said, `We come willingly. [1]

Observatories

Medieval manuscript by Qotbeddin Shirazi depicting an epicyclic planetary model.

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.

File:Ulugh.jpg

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

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 [2][3]has many well equipped observatories, while Jordan [4], Palestine [5], Lebanon [6], UAE [7], Tunisia [8], 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.[9]

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

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

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).
• 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
• J. Ragep (2002). Ancient Roots of Modern Science, Talk of the Nation.
• 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, "Arabic versus Greek Astronomy: A Debate over the Foundations of Science", Perspectives on Science, 8 (2000): 328-41.

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