Astronomer

The astronomer watches the movements of the heavenly bodies, calculates them, and sets the results in tables called zijes. In Islamic sciences the subject was known as ilm al-falak (the science of the spheres) and ilm al-hay'a (the science of configuration), and most Muslim philosophers kept it apart from astrology, the work of the munajjim. ¹ An observatory (rasad, rasathane) is the place where astronomical observations are made. ² Observatories were built at Maragha, Samarkand and Istanbul, and rulers sometimes paid for them. ^{1 3}

The entry notes that the Qur'an speaks often of the heavenly bodies and their stations, and that before Islam the Arabs used the stars to judge the seasons of rain, the seasons of the year and direction. ¹ This shows in their poetry: of 421 poems that mention the Pleiades, twenty-six were composed before 132 AH (750 CE). ¹ The observation produced its own literature, known as books of the rain-stars (kutub al-anwa'), and the entry reports that one scholar listed thirty-seven of them. ¹

The most important witness from the early eighth century is the dome over the hot room of the bath at Qusayr Amra, in western Jordan, which carries ecliptic lines and about four hundred stars. ¹

The entry holds that astronomy in its proper sense began in Islam with translation. Under the caliph al-Mansur an Indian Sanskrit work by Brahmagupta, written around 770 CE, was translated under the title al-Sindhind. ¹ Ibrahim ibn Habib al-Fazari then wrote a zij on the Arab reckoning, giving the basic tables for computing Islamic dates by the lunar calendar. ¹ From Indian writings Muslims learned the first concepts of trigonometry. ¹ Ptolemy's Almagest was translated into Arabic toward the end of the eighth century, and many scholars studied it, wrote commentaries and summaries, among them Thabit ibn Qurra and Ibn Rushd. ¹

The entry says the caliph al-Ma'mun encouraged observation. Scholars were gathered in Baghdad, new instruments were supplied, and observations were made in the Shammasiyya quarter of Baghdad and on the hill of Qasiyun north of Damascus. ¹ Al-Khwarizmi was among the leading astronomers of that age, and his Zij al-Sindhind was translated into Latin and often commented on. ¹

Al-Fargani wrote his books between 218 and 247 AH (833–861 CE), and his Jawami' was translated into Latin and Hebrew. ¹ Al-Battani worked at al-Raqqa between 877 and 919 CE, corrected many of Ptolemy's numerical values from his own observations, and became known in the West in the twelfth century after his zij was translated into Latin. ¹

The entry says that Thabit ibn Qurra proposed a theory of the oscillation of the stars that was later shown to be wrong, and that the ninth sphere added to Ptolemy's system is credited to him. ¹ Al-Biruni completed his al-Qanun al-Mas'udi around 421 AH (1030 CE). ¹ The cosmology of Ibn al-Haytham influenced astronomers in Europe, among them Peurbach and Copernicus. ¹

In the twelfth century some astronomers began to leave Ptolemy's hypotheses. Ibn Bajja, Ibn Tufayl and al-Bitruji returned to the theory of concentric spheres, and the entry thinks the origin of this theory is probably Ibn Tufayl's. ¹ Al-Zarqali in Toledo wrote the Toledan zij, which the Alfonsine tables drew on. ¹

Hulagu built an observatory at Maragha in Azerbaijan and placed it under Nasir al-Din al-Tusi. It held many observing instruments, and its library is reported to have exceeded four hundred thousand books. ¹ After twelve years of observation the Ilkhanid zij was produced. ¹ Later, Ibn al-Shatir revised the sun's inclination to the equator and proposed a new model for the motions of the five planets. ¹

The Samarkand observatory was founded by Ulugh Beg, ruler of Transoxiana and grandson of Timur. The entry says construction began around 1420–21, and that it was completed either in 1421 or in 1427; it finds it reasonable to accept that completion came in the first half of the 1420s. ³ The observatory stood on a rocky hill called Kuhak near Samarkand. Its building was cylindrical, three storeys high and about thirty metres tall. ³ Its main instrument was a meridian arc with a radius of about forty metres. The site also had a large astrolabe, ring spheres, an azimuth half-ring and an observation well. ³

The entry says al-Kashi was invited to Samarkand for the observatory project and took part in building it and in making its instruments; the entry relays this from his own account. He also wrote letters to his father that help in understanding the scholarly life of Samarkand. ³ Astronomers, astrologers and instrument makers worked there. In the introduction to his zij, Ulugh Beg named three of its scholars: al-Kashi, Qadizade al-Rumi, and Ali Qushji. ³

The entry says Ulugh Beg stood at the head of the observations and took an active part in them. The observations lasted more than thirty years, and the observatory remained in use for a time after his death. ³ The observations revised Ptolemy's values for the fixed stars. The obliquity of the ecliptic was fixed at 23°30'17" and the latitude of Samarkand at 39°37'33". ³

A zij is a book of astronomical tables. The term is the one the history of Islamic sciences uses for such tables. ² Ulugh Beg's zij is generally said to have been completed in 841 AH (1437 CE), but the entry thinks he went on working on it until his death. ³ It contains tables of the positions of the heavenly bodies, parameters, and the coordinates of the fixed stars, and its parameters come from observations made at Samarkand itself. ³ It was translated into Arabic and Turkish, commented on by Ali Qushji and Mirim Celebi, and Tashkoprizade called it the best of its kind in its time and the closest to the truth. ³

The entry separates astronomy from astrology clearly. The Ikhwan al-Safa divided the science of the spheres into three branches: the structure of the spheres, stars, their sizes, distances and motions; the use of zijes, the ordering of the calendar and the fixing of dates; and what can be learned from the motion of the spheres about events on earth. ¹ Ibn Sina listed astrology among the natural sciences alongside medicine and physiognomy, but left it out of his definition of astronomy. ¹ The entry adds that astrologers who followed Ptolemy's Tetrabiblos did not accept this separation. ¹

The entry also reports that Ibn Khaldun held that astronomy uses geometry to trace the motions of the heavenly bodies, and gives their positions as far as those motions can be determined, not as they are in reality. ¹ The entry defines the munajjim as a person who practises a discipline based on the belief that the stars influence people and events. ⁴ The Ottoman state had an office of müneccimbaşı, the official in charge of astronomy and astrology affairs together. ⁵

Taqi al-Din al-Rasid was born in Damascus in 932 AH (1526 CE), into a family of Turkish origin. He studied in Damascus and then in Istanbul, from about 957 AH (1550 CE), with scholars including Çivizade and Ebussuud. ⁶ He taught in two madrasas in Cairo, and acted as deputy for Çivizade when Çivizade was appointed judge of Egypt. ⁶ He returned to Istanbul in 978 AH (1570 CE), and a year later Selim II appointed him müneccimbaşı. ⁶

He began observing from the Galata Tower, and then, with Murad III's permission, built an observatory on the slopes of Tophane in 985 AH (1577 CE), with a library. ⁶ The Samarkand entry dates the Tophane observatory to 1575, under Murad III's patronage. The two dates differ and both are recorded here. ³ The Takiyyüddin entry calls it the only observatory in Ottoman history. ⁶ The entry says he built on the accumulated work of Samarkand, and it compares his observatory with Tycho Brahe's Uraniborg. ^{6 3}

The observatory drew opposition, which the entry says was tied to political rivalries. The Shaykh al-Islam Kadizade Ahmed Shams al-Din issued a fatwa holding that observatories bring ruin on the lands that have them. On 4 Dhu al-Hijja 987 AH (22 January 1580 CE) an imperial decree ordered the observatory and its instruments destroyed. ⁶ The entry says that he withdrew after this and died in Istanbul. ⁶

The entry treats Taqi al-Din as one of the last great representatives of classical Islamic astronomy. His works include tables using decimal fractions, sine and tangent tables for each degree, a book on optics, and a book on mechanical clocks that show seconds. ⁶

The entry says that al-Andalus left the field of astronomical research after its conquest, and that research revived in Iran after the Mongol invasion. ¹ Development at Samarkand stopped after Ulugh Beg's death, but his zij influenced European astronomy through its Latin translations, and the Samarkand tradition is traced in the Ottoman, Safavid and Babur states. ³ The observatories built by Sawai Jai Singh II in India in the eighteenth century are another instance of its influence. ³

The modern observatory came later. The Ottomans founded the Kandilli observatory in 1868 as the first modern observatory in the state; it now works within Boğaziçi University. ²

• TDV İslâm Ansiklopedisi, "İLM-i FELEK", Tevfik Fehd, vol. 22, pp. 126–129. ¹
• TDV İslâm Ansiklopedisi, "SEMERKANT RASATHÂNESİ", Hasan Umut, vol. 36, pp. 486–487, with its digital version of 23 February 2026. ³
• TDV İslâm Ansiklopedisi, "TAKIYYÜDDİN er-RÂSID", Hüseyin Gazi Topdemir, vol. 39, pp. 454–456. ⁶
• Cross-reference and definition pages with no printed page numbers: "ASTRONOMİ" ⁷; "MÜNECCİM" ⁴; "MÜNECCİMBAŞI" ⁵; "RASATHÂNE" ².
• Works named in the entries' bibliographies, not read for this record: Sayılı, The Observatory in Islam; Kennedy, On the Contents and Significance of the Khāqānī Zīj; Sédillot, Prolégomènes des tables astronomiques d'Oloug-Beg; Rybka, "Mouvements des planètes dans l'astronomie des peuples de l'Islam".