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Observatories

By:
Yavuz Unat, Salim Ayduz
Source:
The Oxford Encyclopedia of Philosophy, Science, and Technology in Islam What is This? Includes complete coverage of Islamic philosophy, sciences, and technologies from the classical through contemporary periods.

Observatories

In Islamic civilization, “observatories” were known as raṣadkhana, which comes from the Arabic word raṣad (astronomical observation). An observatory was also known as a bayt al-raṣad or marṣad. Following the model of the earlier Greek “observational posts,” raṣadkhana were founded for the purpose of performing regular astronomical observations and mathematical studies, which involved large, elaborate measuring instruments, many of which were built by Muslim scholars.

Astronomy (ʿilm-i hayʾa) has attracted attention in the Islamic world since the eighth century CE. Al-Manṣūr (r. 754–775) was the first caliph to be interested in the study of the cosmos, and most succeeding rulers followed him in this regard. It wasn’t until the reign of the ʿAbbāsid caliph al-Maʾmūn (813–833), however, that systematic astronomical observations began. Although one probable reason for this enterprise was the the caliph’s interest in astronomy, another was likely his desire replace the astronomical tables that had been prepared in the past by the Indian-Persians and the Greeks with current observations made by Muslim astronomers. The desire to begin systematic—and accurate—astronomical data collection led naturally to the need for observatories. The most important reason for the establishment of observatories was the increasing size of the instruments required for observation and thus the need to house them. Although Islamic observatories were mostly founded by rulers, they were not considered permanent institutions and for the most part were short-lived.

Rather than primarily institutions of astrological study, Islamic observatories were scientific institutions devoted to research on the questions of astronomical science and its auxiliary disciplines. Their objective was to create new astronomical handbooks of tables (zīj) based on observations made using their instruments. Because of this new data, old astronomical handbooks were corrected and better versions were created.

Results obtained in observatories were recorded in catalogues called zījāt, which contained information regarding the trigonometry of orbital periods, global astronomy, calendar types and formation, projection methods, construction and use of observation tools, astrology, and determination of prayer time. Ar-Raqqah Observatory set up by Albategnius (al-Battānī) used trigonometry in the tenth century. They also contained numerical tables intended to solve standard problems, such as how to measure time and to compute planetary and stellar positions (Kennedy 1956).

Shammāsiyya and Qāsīyūn Observatories.

The first Islamic observatory was the Shammāsiyya Observatory, established in Baghdad in the ninth century, during the reign of the caliph al-Maʾmūn. The second was the Qāsīyūn Observatory, founded by al-Maʾmūn in Damascus. Each of these observatories featured meticulously designed tools, a special working location, and a scientific committee that consisted of scholars who cooperated both to design a research program for the facility and to protect the interests of al-Maʾmūn, a caliph who held science in high esteem.

Because measurements regarding geodesy were not standardized, Islamic astronomers researched the dimensions of the Earth using their own methods and measurement units. Under the order of al-Maʾmūn, they measured the distance between two locations and used their understanding of angles to determine the 1 degree arc of meridian and use it to find the diameter and circumference of the Earth (Sayılı, 1960, p. 85). Although accounts from the time are not completely consistent, the measurements may have been conducted between two locations in the desert of Sinjār (west of Mosul) or between Tadmur and ar-Raqqah in Syria. As a result of these two measurements, the 1 degree arc of meridian was calculated as being approximately 112 kilometers, which is very close to the currently accepted value.

Ar-Raqqah Observatory.

Al-Battānī (Albategnius, c. 858–929), one of the most important astronomers and mathematicians of the tenth century, hailed from the Ḥarrān region (currently Urfa, Turkey) and was the author of al-Zīj al-Sabī. He established a private observatory in ar-Raqqah where he made relatively important observations between the years 887 and 918. He was interested in solar and lunar eclipses, calculated the duration of the seasons with great accuracy, and succeeded in determining the inclination of the ecliptic. He assessed the solar year at 365 days, 5 hours, 46 minutes, and 24 seconds, and he found that the longitude of the solar apogee had increased by 16° 47' since the observation of Ptolemy.

Hamadān Observatory.

Ibn Sīnā (c. 980–1037) was not only a famous physician but also an astronomer. He was a friend of ʿAlāʾ al-Dawla, the amīr of Isfahan. At the request of Ibn Sīnā, ʿAlāʾ al-Dawla ordered the establishment of an observatory in Hamadān so that Ibn Sīnā could prepare a new astronomical table. Together with his student Abū ʿUbayd al-Jūzjānī (d. 1070), Ibn Sīnā, invented a device that measured the azimuth and height at the observatory (dhāt al samt vaʾl irtifā, or azimuthal semicircle). One part of this device resembles a micrometer, an instrument invented in 1670 that is still used today to measure the very small angular positions between two celestial bodies). Not surprisingly, Ibn Sīnā’s and al-Jūzjānī’s device provided great precision in angular measurements. Sources do not provide adequate information to determine whether zījāt were prepared at this observatory.

Ibn Yūnus’s Observatory at Muqaṭṭam.

During the tenth century, the Fāṭimid caliph al-Hākim bi Amr Allāh (996–1021) built what is usually described as a “well-equipped” observatory at Mount Muqaṭṭam, near Cairo. According to some writers, the observatory formed a part of the House of Knowledge founded by al-Hākim in Cairo. The Egyptian astronomer and mathematician Ibn Yūnus (d. 1009) made extremely precise observations in this observatory between 977 and 1007, which he published under the title al-Zīj al-Ḥākimī al-kabīr (The Hākimī Tables) (Sayılı, 1960).

Malikshah Observatory.

In 1073 the Seljuk sultan Jalāl al-Dīn Malikshah (r. 1072–1092) and his grand vizier, Niẓām al-Mulk, invited the famous mathematician and astronomer ʿUmar Khayyām (1048–1131) to build an observatory, along with various other renowned scholars of the time, including Abū al-Muẓaffar Isfizārī, Maimun ibn Nacīb al-Wāsıtī, Abdurrahman Hārisi, and Abū al-Fatḥ ʿAbd al-Raḥmān al-Khāzinī in Isfahan. ʿUmar Khayyām was appointed as head of the observatory and given the task of correcting the solar calendar for revenue collection and other administrative purposes. But instead of fixing the previously used calendars, Khayyām decided to create a new calendar that would adjust to the different seasons for the sultan and carried out his observations based on this objective. He completed his research in 1079 and produced both an astronomical table called Zīj-i Malik-Shāhī (Astronomical Handbook with Tables for Malikshah) and a calendar titled al-Tārīkh-al-Jalāli (Jalāl al-Dīn Calendar) for Jalāl al-Dīn Malikshah. The Jalālī calendar has an error margin of 1 day every 5,000 years, whereas the Gregorian calendar used today has an error margin of 1 day every 3,330 years. Unlike other observatories that were relatively short-lived, the Malikshah observatory remained in operation for nearly twenty years.

Marāgha Observatory.

The Mongol conqueror-prince Hūlāgū (d. 1265) founded the observatory at Marāgha (located south of Tabrīz) in 1259 and appointed Naṣīr al-Dīn al-Ṭūsī (1201–1274) as its head. The observatory included several buildings, a very large library, and an extensive collection of instruments, and was staffed with a number of prominent scholars. The Marāgha observatory represents an important advancement in the development of Islamic observatories in terms of both the precision of its astronomical instruments and the number of mathematicians and astronomers working there. One tool built at the observatory was the dhāt al-rubayn, which could measure the height of heavenly bodies from any angle. It had been previously used by Ibn Sīnā but was improved at the Marāgha observatory by al-Ṭūsī. Another instrument employed in the observatory was dhāt al-cuyūb vaʾl-sahm (the sine and versed sine instrument), which was used for measuring the azimuth and sines of angles of elevation (Sayılı, 1960). The results of the observations made at Marāgha Observatory were compiled by al-Ṭūsī, and in 1271, after twelve years of observation and calculation, they were completed and gathered in a book called Zīj-i Ilkhānī (“il-khan” was one of Hūlāgū’s titles, meaning subordinate khan). After the completion of the zīj, work at Marāgha seems to have slowed, although the institution continued to exist for many years.

Samarqand Observatory.

The period from the end of the fourteenth century through the fifteenth century was a bright one for Turkistan. Iran and Turkistan were combined under the government of the Timurid dynasty (c. 1370–1507), established by Timur (1336–1405), who brought a set of scientists to the capital city of Samarqand. While Timur and his successors ruled the region, science and culture flourished in Transoxiana and Samarqand. Education advanced in these cities as well, particularly during the reign of Uluğ Bey, son of Timur’s grandchild Shāhrukh.

Uluğ Bey was both a ruler and a scholar. He was deeply interested in astronomy and mathematics, and he interacted with these sciences during his lifetime. He took courses at the madrasah he established and participated in discussions as well as giving lectures. Uluğ Bey spent most of his time with scientists and gathered many scientists around him. He thus had the opportunity to learn from famous scientists such as Ghiyās al-Dīn Jamshīd al-Kāshī and Qāḍīzāde Rūmī.

In 1429 Uluğ Bey completed construction of a large, round three-story observatory in his madrasah. Al-Kāshī was the first director of the observatory, and Qāḍīzāde Rūmī was appointed to that position after his death in 1429. However, Uluğ Bey always remained the head, or the “holder of the observatory,” and al-Kashi used the term “Holder of Observatory” for Uluğ Bey. Al-Qushjī became the director of the observatory after Qāḍīzāde Rūmī.

The Samarqand observatory is of note for the astronomical instruments that were used there. One of the most important devices used was the mural quadrant. This device, which was also used to measure Kuhek Hill, on which the observatory was built, was 50 meters tall—the same height as the Hagia Sophia mosque in Istanbul. The dial of the quadrant was constructed as a part of the observatory, with the upper 60 degrees placed above ground and the lower 30 degrees below ground. One part of the dial was revealed as a result of an excavation by the Russian archaeologist V. L. Viatkin in 1908.

Uluğ Bey, al-Kāshī, Rūmī, and al-Qushjī compiled the observations and research carried out at the observatory in the Zīj-i Ulugh Beg (Astronomic Tables of Uluğ Bey). It was written in Persian between 1437 and 1440 and later translated into Arabic and Turkish. Zīj-i Ulugh Beg is composed of four volumes and contains trigonometric, astronomical, geographic, and astrological tables.

Istanbul Observatory.

The first observatory of the Ottoman Empire was founded in Istanbul by Taqī al-Dīn ibn Maʿrūf (1526–1585). Born in Damascus, Taqī al-Dīn engaged in traditional religious training and then in the study of advanced mathematics and astronomy in Damascus and Egypt. After completing his education, he worked as both a teacher and a judge (qāḍī; kadi). During this period, he travelled frequently to Istanbul, making the acquaintance of prominent statesmen and scholars, before finally settling in Istanbul in 1570. The following year, the Ottoman sultan Selīm II (r. 1566–1574) appointed Taqī al-Dīn to the position of chief astronomer (munajjimbashilik). Because there wasn’t yet an observatory in Istanbul, he conducted his observations from Galata Tower or from another high point in the city.

Among the close acquaintances Taqī al-Dīn had made during his travels was the grand vizier Sokullu Mehmed Pasha, who presented Taqī al-Dīn to the new sultan, Murād III (r. 1574–1595). Taqī al-Dīn proposed to the sultan that a new observatory be built in Istanbul to correct errors in Uluğ Bey’s astronomical tables, which Taqī al-Dīn claimed had caused mistakes in calculations. Sultan Murād, who had an interest in astronomy and astrology, was pleased to be the patron of an Ottoman observatory that would rival the one at Samarqand. He ordered work on the new observatory to begin immediately and even provided the necessary finances. While construction was underway, Taqī al-Dīn continued to make observations from the Galata Tower until 1577, when he moved to the partially completed Dār al-Raṣad al-Jadīd (new observatory).

Constructed on a height in Tophane, on the European side of the Bosporus strait, the observatory consisted of a large building, a small building, and a well (çah-i raṣad) and housed a library devoted to astronomy and mathematics. It was operated by a team of sixteen people, including eight “observers” (rāsid), four clerks, and four assistants. The astronomical instruments used at the observatory included many from the old Islamic observatories, which Taqī al-Dīn reproduced with great care, but also several that he invented. Interestingly, Taqī al-Dīn’s instruments (new and old) were similar but of superior quality to those of his contemporary, the Danish astronomer Tycho Brahe (1546–1601), who had built an observatory on the island of Hven.

The instruments Taqī al-Dīn carefully reproduced for his observatory included (1) an armillary sphere (an instrument consisting of six concentric bronze rings that is used for measuring latitudes and longitudes), which was invented by Ptolemy; (2) a mural quadrant (a large device that measured angles, used for locating the position of the sun and the stars); (3) an azimuthal semicircle (an angular device sitting perpendicular to a horizontal copper ring, which measured the altitude and angular position of the stars); (4) a parallactic ruler (in instrument consisting of three long pieces of wood used to measure the distance to the moon); (5) a dioptre, an instrument “with two holes,” used to measure eclipses and diameters; and (6) an “instrument with cords” to determine the equinoxes of spring and fall.

Taqī al-Dīn’s observatory also contained three instruments of his own invention that paralleled but had greater precision than those of Tycho Brahe: the astronomical clock, the wooden quadrant, and the mushabbaha biʾl-manâtiq (sextant). Taqī al-Dīn’s automatic mechanical clock operated by a mechanism of cogwheels and consisted of three dials to show hours, degrees, and minutes, which were each divided into five seconds. Not only was it the first of its kind, but it provided the precision necessary for astronomical calculations. The wooden quadrant was a quarter of a circle that was constructed from wooden rulers and could measure the altitudes of the stars. Used to determine the distance between stars, the mushabbaha biʾl-manâtiq consisted of three rulers attached to one another at one end, with an arc attached to the one of the rulers at the other end. Taqī al-Dīn’s mushabbaha biʾl-manâtiq and Tycho Brahe’s similar sextant have been hailed as among of the greatest achievements of the sixteenth century (Tekeli, 2005).

As a result of the instruments he invented and the new methods he employed, Taqī al-Dīn was able to provide novel solutions to astronomical problems and to provide the most precise observations of his time. Although his first task was to correct the Uluğ Bey astronomical tables, he painstakingly observed solar and lunar eclipses as well as recording round-the-clock observations of a comet that remained in the skies over Istanbul for an entire month in 1577. Among his accomplishments were to replace the sexagesimal numerical system with a decimal one and to prepare trigonometric tables based on decimal fractions. He was able to calculate the obliquity of the ecliptic as 23º 28' 40", which is remarkable close to the currently accepted value of 23º 27'. Using a new method for calculating solar parameters, he determined that the annual movement of the sun’s apogee was 63 seconds. The generally accepted figure today is 61 seconds, whereas Copernicus calculated it at 24 seconds, and Tycho Brahe arrived at a figure of 45 seconds. Taqī al-Dīn was a prolific writer as well as a researcher, producing books—and poems—on mathematics, mechanics, and optics in addition to astronomy. He wrote the first Ottoman book on automatic machines, Turuq al-saniyya, and his astronomical tables were collected under the title Sidratu muntahaʾl-afkār fī malakūt al-falak al-dawwār (Culmination of thoughts in the kingdom of rotating spheres).

Despite the quality of the work produced there, the Istanbul observatory was torn down on 22 January 1580 by order of Sultan Murād. Taqī al-Dīn had interpreted the comet of 1577 as a sign of upcoming victory over the Persians, which in fact occurred but at a cost of heavy casualties. When several dignitaries proceeded to die within a short period of time followed by the onset of a plague, the Shaykh al-Islām Aḥmad Shams al-Dīn issued a legal opinion (fatwā) condemning the observatory as the cause of the disasters, and Admiral Kılıç Ali Pasha carried out the sultan’s orders to destroy it. The demolition of the Istanbul observatory marked the end of astronomy in the Ottoman Empire. The Ottomans would try to follow the new sciences developing in the West, including Copernican astronomy, after the seventeenth century, but another observatory would not be built until 1868. This facility, originally named Rasadhane-i Āmire (Imperial Observatory), was originally designed to disseminate weather forecasts by cable to other meteorological stations. Its first director was Aristide Coumbary (Coumbary Efendi), who had come to Turkey to develop the telegraph cable network. Destroyed in 1909, the observatory was later rebuilt and is known today as the Kandilli Observatory and Earthquake Research Institute (KOERI). In 2001 the KOERI began to develop a real-time automated seismic data-processing system to enable the rapid location of earthquakes.

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