As astrology was one of the very first scientific disciplines to be adopted by the ‘Abbāsid in their assimilation of Persian cultural it followed automatically that that they also adopted astronomy; you need astronomy in order to do astrology. Also, the practice of Islam itself required both the determination of the times for the five daily prayers as well as the qibla the geographical direction of the Kaaba in the Sacred Mosque in Mecca both astronomical problems.
Pre-Islamic Arabic society already possessed a fairly simple astronomy based on observation but not an advanced mathematical astronomy as had been developed by the Babylonians, Greeks, and Indians. Their first appropriations were from Persian and Indian astronomy. Indian astronomy had been strongly influenced by Greek astronomy since the time of Alexander the Great.
Ptolemaeus’ Mathēmatikē Syntaxis contained many astronomical tables along with the vast amount of theoretical geometrical information on how to determine that data from the orbits of the celestial bodies. Astrologers and other practical users of astronomy wanted the data without the theoretical content, so Ptolemaeus also published his Handy Tables containing the tables and instructions on how to use them. These proved to be very popular and the first astronomical texts produced in the Islamic Empire were translations of similar astronomical tables from India, the most notable being Zīj as-Sindhind (Great astronomical tables of the Sindhind) translated from Sanskrit by Muhammad ibn Ibrāhīm al-Fazārī (died 796 or 806) and Yaʿqūb ibn Ṭāriq (died 796). The historian of science Ṣāʿid al-Andalusī (1029–1170) claimed that Ibn Sa’d (784/5–845) and Muhammad ibn Musa al-Khwārizmī (c. 780–c. 850) were also involved in the translation but in fact al-Khwārizmī’s Zīj as-Sindhind, whilst very similar is different. Also translated during the same period Zij al-Shah a Persian set of astronomical tables also based on Indian data.
Zīj (plural Azyāj, modern English plural zījes) is derived from a Middle Persian word, zih or zīg “cord”. The term is believed to refer to the arrangement of threads in weaving, which was transferred to the arrangement of rows and columns in tabulated data. These early translations set a standard for astronomical texts, zīj, astronomical books that tabulates parameters used for astronomical calculations of the position of the sun, moon, stars, and planets being produced by many leading Islamic astronomers and being the first Islamic astronomical texts that were translated into Latin during the twelfth century Scientific Renaissance. Such tables were of course of practical use for astrologers, but also combined with instruments for determining prayer times and the qibla.
From these simple beginning medieval Islamic astronomy expanded into a massive field of study over several centuries and I can only offer a sketch here, highlighting some of the major participants and developments. Its influence can be measured on the number of Arabic star names that are still in use today.
Islamic astronomy was based on Ptolemaic astronomy and there are reports of at least five translations of his Mathēmatikē Syntaxis during the ‘Abbāsid Caliphate of which only two survive, the earliest (829-830) is that of Al-Ḥajjāj ibn Yūsuf ibn Maṭar (786–833) done during the reign of al-Ma’mun (786–833), who reigned from 813. The second surviving translation was by Hunayn ibn Ishaq al-Ibadi (808–873), a Nestorian Christian, who was a very prolific translator. His translation was corrected by Thābit ibn Qurra (826 or 836–901), a Sabian of Harran, who was also a prolific translator. The Arabic influence can also be seen in the fact that Ptolemaeus master work is today mostly known was the Almagest, a version of its Arabic title al-majisṭī, with al meaning the and magesti being a corruption of Greek μεγίστη megístē ‘greatest, translated into Almagestum in Latin in the twelfth century. The Greek title Mathēmatikē Syntaxis later became Hē Megalē Syntaxis (Ἡ Μεγάλη Σύνταξις, “The Great Treatise”; Latin: Magna Syntaxis) not because it was considered the “greatest” work on astronomy, as is often falsely claimed but because Ptolemaeus produced two collected works on astronomy a small one and a big one, the Mathēmatikē Syntaxis being the big one, hence Hē Megalē Syntaxis.
Although the Almagest provided the back bone of medieval Islamic astronomy the Islamic astronomers did not in any way venerate it but as we will see challenged, criticised, and corrected it, some even rejected it.
Habash al-Hasib al-Marwazi (766 – d. after 869) is typical of the early medieval Islamic astronomers, a Persian astronomer, mathematician, and geographer who worked under the caliphs al-Maʾmūn (786–833) and al-Muʿtaṣim biʾllāh (796–842) making observations at the al-Shammisisyyah observatory in Baghdad. His zījes are in the Indian style and show no Ptolemaic influence.
The Banū Mūsā, or sons of Mūsā, were the three sons– Abū Jaʿfar, Muḥammad ibn Mūsā ibn Shākir (before 803 – February 873), Abū al‐Qāsim, Aḥmad ibn Mūsā ibn Shākir (d. 9th century), Al-Ḥasan ibn Mūsā ibn Shākir (d. 9th century)–of the Persian, astronomer, astrologer Mūsā ibn Shākir employed by the caliph al-Maʾmūn, who following their father’s death educated the three and provided them with employment in Baghdad. They are best known as prolific translators of Greek works from Byzantium although they also produced around twenty original works on astronomy, astrology, mathematics, and technology of which only three have survived. Their work on astronomy was Ptolemaic and concentrated on theoretical aspects rather than being based on their own observations. Of greatest interest they challenged the real feasibility of the Aristotelian–Ptolemaic cosmological model arguing that friction between the crystalline sphere would hinder the orbits. They treated the cosmological model presented by Ptolemaeus as real and not just as a theoretical mathematical model designed to save the phenomena.
Born in Basra, Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham (c. 965–c. 1040)–known in Latin as Alhazen–is best known for his work in optics but he also wrote on astronomy following the line started by the Banū Mūsā. In his Epitome of Astronomy, he argued against a philosophical and for a physical astronomy. In his Al-Shukuk ala Batlamyus (“Doubts on Ptolemy”), whilst accepting a Ptolemaic geocentric cosmos he strongly criticised various element of Ptolemaeus’ astronomy.
One of the most influential ‘Abbāsid astronomers was Abū al-ʿAbbās Aḥmad ibn Muḥammad ibn Kathīr al-Farghānī (c.800–870)–known in Latin as Alfraganus–who wrote an astronomical textbook Kitāb fī Jawāmiʿ ʿIlm al-Nujūm (A Compendium of the Science of the Stars) sometime between 833 and 857. This is a descriptive summary of the Almagest, which is however corrected using the findings and calculations of earlier Islamic astronomers. An easy to understand, highly accessible presentation of Ptolemaic astronomy it was widely in read in both the Islamic Middle Ages and also in Latin translation in Europe.
As already noted in the previous episode of this series the Neoplatonist Abu Nasr Muhammad al-Farabi (c.870–950) played a major role in making the works of both Plato and Aristotle known in medieval Islamicate culture. He viewed astronomy as descriptive and in his comprehensive Arabic classification of the sciences in his Kitab al-ibsa al ‘Ulum (Catalogue of Sciences), he separated mathematical astronomy from science thus adhering to a Platonic saving of the phenomena rather that a realistic, physical astronomy as propagated by the Banū Mūsā and al-Haytham.
Abū ʿAbd Allāh Muḥammad ibn Jābir ibn Sinān al-Raqqī al-Ḥarrānī aṣ-Ṣābiʾ al-Battānī (before 858 – 929)–known in Latin as Albategnius–was born in Harran in Bilād al-Shām (Islamic Syria) the son of Jabir ibn Sinan al-Harrani, an astronomical instrument maker. There is circumstantial evidence that father was a Sabian but al-Battānī was a Muslim. He established his own observatory in Raqqa, now in Syria. He used large astronomical instruments which enabled him to make very accurate observations and he became one of the most important medieval, Islamic observational astronomers. He was a convinced Ptolemaic astronomer and his Kitāb az-Zīj aṣ-Ṣābi’, written around 900, a very major set of astronomical tables shows almost no Hindu or Sassanian influence. The book was highly influential in Latin transition as De motu stellarum (On stellar Motion) in medieval and Renaissance Europe, even being printed in Nürnberg from a manuscript owned by Regiomontanus in 1537, with a second printed edition appearing in Bologna in 1645.
One of the most well known books of medieval, Islamic astronomy is the Kitāb suwar al-kawākib (The Book of the Fixed Stars) by Abd-al-Raḥmān ibn ʿOmar Ṣūfī, Abu’l-Ḥosayn, (903– 986), written in 964. Abd al-Rahman al-Sufi was a Persian astronomer living and working in the court of the emir of the Buyid dynasty ʿAḍud al-Dawla (936–983) in Isfahan south of Tehran. He was an avid translator into Arabic of Hellenistic astronomy that had been centred on Alexandria. The Kitāb suwar al-kawākib compares Greek constellations and stars as described by Ptolemaeus in the Almagest with Arabic ones linking those that are the same. The book contains two pictures of each of the forty eight Ptolemaic constellation one as seen from the Earth and the other, the so-called god’s eye view, as seen from outside the celestial globe. The book contains the first depiction of the Andromeda nebula as a small cloud in front of the mouth of the constellation Fish.
Abu al-Hasan ‘Ali ibn ‘Abd al-Rahman ibn Ahmad ibn Yunus al-Sadafi al-Misri (c. 950–1009) usually known simply as Ibn Yunus was an Egyptian Arabic astronomer renowned for the quality and accuracy of his observations. He worked from his observatory near Fustat, now part of Cairo, that was built for him by the then new Fatimid dynasty. Once again his most famous astronomical work was a zīj his al-Zij al-Kabir al-Hakimi written by order of Fatimid Caliph Al-Aziz in the year 380 AH/990 and completed in 1007. The historian of astronomy, Noel. Swerdlow (1941–2021) described it as “a work of outstanding originality of which just over half survives.”
The major Islamic polymath Abu Rayhan Muhammad ibn Ahmad al-Biruni (973–after 1050), a Khwarazmian scholar, who wrote on everything also wrote about astronomy. Famous for his description of India and its culture, his Taḥqīq mā li-l-Hind is an extensive commentary on Indian astronomy consisting mostly of translation of the work of Aryabhatta (476–550). He discussed Aryabhatta’s acceptance of a geocentric system with diurnal rotation of the Earth, a theory originally proposed by Heraclides Ponticus (c. 390–c. 310 BCE), in his Miftah-ilm-alhai’a (“Key to Astronomy“), which is no longer extant, but in the end rejected it Al-Biruni rejected the theory. In a heated debate with Ibn Sina, al-Biruni rejected the physics of Aristotle.
Abu Sa’id Ahmed ibn Mohammed ibn Abd al-Jalil al-Sijzi (c. 945 – c. 1020) a Persian mathematician, astrologer, and astronomer, who corresponded with al-Biruni, defended the theory of diurnal rotation in his al-Qānūn al-Masʿūdī.
Abū Ḥāmid Muḥammad ibn Muḥammad aṭ-Ṭūsiyy al-Ġazzālīy (c. 1058–1111), known as al-Ghazālī, famously launched a philosophical attack on the work of Ibn Sina and al-Farabi Tahāfut al-Falāsifa (The Incoherence of the Philosophers) in which he rejected the Greek astronomy of Ptolemaeus arguing that the motion of the celestial bodies was the direct result of God’s will. However, rather than leading to a decline in astronomy as is often claimed, the presence of science and philosophy in religious texts increased after Ghazālī’s attacks.
Most of the astronomers discussed up till now used comparatively small local observatories to carry out their astronomical work but there were a series of major observatories built during the Islamic period beginning with the observatory built in Maragheh, in the East Azerbaijan Province of Iran, by the Mongol ruler Hulegu Kahn (c. 1217–1265) notorious for having sacked the ‘Abbāsid capital Baghdad in 1258.
The director of the Maragheh observatory was the Persian polymath Muhammad ibn Muhammad ibn al-Hasan al-Tusi (1201 – 1274). As others before him al-Tusi produced a zīj based on his new very accurate observation, Zīj-i Īlkhānī (Ilkhanic Tables).
He heavily criticised Ptolemaeus’ planetary models and in particular his use of the equant point, a bone of contention for many astronomers over the centuries, and developed new models utilising his own invention the geometrical construction, now known as the Tusi-couple.
Other notable astronomers working at the Maragheh observatory including the Arabic astronomer Al-Urdi (full name: Moayad Al-Din Al-Urdi Al-Amiri Al-Dimashqi) (died 1266) born in Syria, who had previously worked in Damascus. His most notable works were Risālat al-Raṣd, a treatise on observational instruments, and Kitāb al-Hayʾa a work on theoretical astronomy.
Also, the Persian astronomer Qotb al-Din Mahmoud b. Zia al-Din Mas’ud b. Mosleh Shirazi (1236–1311), who was born into a Sufi family in Karezun. After a short stay in Maragheh he moved on to Qazvin, Isfahan, Baghdad, and Konya in Anatolia. He wrote several astronomical texts most notably Nehāyat al-edrāk fi dirayat al-aflak (The Limit of Accomplishment concerning Knowledge of the Heavens) 1281, and Al-Tuhfat al-Shahiya (The Royal Present) 1284. Both presented his models for planetary motion, improving on Ptolemaic principles. In his The Limit of Accomplishment concerning Knowledge of the Heavens, he also discussed the possibility of heliocentricity.
Shams al-Din Muhammad b. Ahmad al-Khafri al-Kashi (died 1550),known as al-Din Khafri a Persian theologian and astronomer wrote al-Takmila fi sharh al-tadhkira (The complement to the explanation of the memento) This commentary by al-Khafri is a technical commentary on a work written by al-Sharif al-Jurjani on the astronomical critique by Nasir al-Din al-Tusi’s of Ptolemaic astronomy, al-Tadhkira fi ‘ilm al-Hay’a (Memento in astronomy).
Also influenced by the Maragheh astronomers was the Arabic astronomer Abu al-Ḥasan Alāʾ al‐Dīn bin Alī bin Ibrāhīm bin Muhammad bin al-Matam al-Ansari (1304–1375) known as Ibn al-Shatir, who was born in Damascus and studied astronomy in Cairo and Alexandria. He returned to Damascus where he was appointed time keeper of the Umayyad Mosque. Ibn al-Shatir presented a radical reform of the Ptolemaic planetary models in his kitab nihayat al-sul fi tashih al-usul (The Final Quest Concerning the Rectification of Principles) in which he incorporated the so-called Urdi lemma, which allowed an equant in an astronomic model to be replaced with an equivalent epicycle (the Tusi-couple) that moved around a deferent centred at half the distance to the equant point. Like Ibn a-Haytham, Ibn al-Shatir rejected philosophical astronomy and Aristotelian cosmology. Promoting instead an astronomy of models based on empirical observations. Perhaps his most notable achievement was his new, highly accurate, double epicycle lunar model, the first lunar model which matched physical observations.
The Timurid sultan Mīrzā Muhammad Tāraghay bin Shāhrukh (1394–1449), better known as Ulugh Beg, a moniker meaning Great Ruler, was not just a patron of astronomy like other rulers but was himself a passionate mathematician and astronomer and a notable linguist.
During his reign, he turned his capital Samarkand into an international centre for learning. Inspired by a visit to the Maragheh observatory in his youth he constructed an enormous observatory in Samarkand in 1428 and brought some of the leading Islamic astronomers of the fifteenth century to work with him there.
The Timurid astronomer Ala al-Dīn Ali ibn Muhammed (1403–1474), known as Ali Qushji, was born in Samarkand the son of one of Ulugh Beg’s falconers.
After studying in Samarkand, he moved to Kerman in Persia the on to Herat before returning to Samarkand where he presented his work on the Moon to Ulugh Beg, who appointed him to the observatory, where he worked until Ulugh Beg was assassinated. Following Ulugh Beg’s death he again travelled around to Herat, Tashkent, Tabriz and finally Constantinople where he worked under the Ottoman Sultan Mehmed II.
He wrote nine works on astronomy, two in Persian and seven in Arabic but his most important work was his Concerning the Supposed Dependence of Astronomy upon Philosophy in which he totally rejected Aristotelian physics and natural philosophy from astronomy, developing a purely empirical and mathematical astronomy. He was another Islamic astronomer after al-Biruni and al-Sijzi, who investigated the possibility of diurnal rotation.
The Persian astronomer Ghiyāth al-Dīn Jamshīd Masʿūd al-Kāshī (c. 1380–1429) was born in Kashan in Iran part of the Timurid Empire and he like many others was drawn to Samarkand and Ulugh Beg and his observatory. Al-Kāshī produced the Khaqani Zīj which was an updated improved version of al-Tusi’s Zīj-i Īlkhānī. He also wrote Sullam al-sama’ (The Ladder of the Sky) an astronomical treatise on the determination of the size and distance of celestial bodies and a treatise on astronomical observational instruments.
The Maragheh observatory also served as inspiration and model for the observatory built by Turkish astronomer Taqi ad-Din Muhammad ibn Ma’ruf ash-Shami al-Asadi (1526–1585) for his patron Sultan Murad III (1546–1595) in Constantinople in 1574.
and the observatories built by Sawai Jai Singh II (1688–1743) in Delhi, Mathura, Benares, Ujjain and more famously in his capital Jaipur in India.
Jantar Mantar Observatory in Jaipur Source: Wikimedia CommonsUp till now all of the astronomers we have briefly sketched lived and worked in the Islamic East, early under the ‘Abbāsid Caliphate but then later on under the Fatimid Caliphate and still later under the Timurid Sultanate. Another astronomical scene developed in the Islamic West in al-Andalus, the Iberian Peninsula, under a Umayyad Caliphate and its successors.
The first astronomer of note was Abū Bakr Muḥammad ibn Yaḥyà ibn aṣ-Ṣā’igh at-Tūjībī ibn Bājja (c. 1085 – 1138), known in Latin as Avempace.
An Arab born in Zaragoza he was an important philosopher but also a polymath, who wrote about astronomy. The Jewish philosopher Maimonides (1138–1204) wrote:
I have heard that Abu Bakr [Ibn Bajja] discovered a system in which no epicycles occur, but eccentric spheres are not excluded by him. I have not heard it from his pupils; and even if it be correct that he discovered such a system, he has not gained much by it, for eccentricity is likewise contrary to the principles laid down by Aristotle…. I have explained to you that these difficulties do not concern the astronomer, for he does not profess to tell us the existing properties of the spheres, but to suggest, whether correctly or not, a theory in which the motion of the stars and planets is uniform and circular, and in agreement with observation.
Abū Bakr Muḥammad bin ʿAbd al-Malik bin Muḥammad bin Ṭufayl al-Qaysiyy al-ʾAndalusiyy (c. 1105 – 1185), Ibn Tufail, known in Latin as Abubacer Aben Tofail, was an Arab born near Granada, who was a student of Ibn Bājja and is said to have completely rejected the astronomical models of Ptolemaeus, reverting to the homocentric spheres of Aristotle. He held important political posts and was the vizier and physician to Abu Ya`qub Yusuf (1135–1184) the first Almohad Caliph to whom he recommended Abū l-Walīd Muḥammad Ibn ʾAḥmad Ibn Rušd (1126–1198), known in Latin as Averroes, as his successor.
Ibn Rušd was one of the most important Islamic philosophers and a mainstream Aristotelian, rejecting the Neoplatonism of the ‘Abbāsid philosopher, particularly that of Ibn Sina. Because of his work promoting Aristotle he became known as the Commentator in medieval Europe. Rejecting Ptolemaeus, he strongly propagated the Aristotelian homocentric spheres model of astronomy.
Nur ad-Din al-Bitruji (died 1204), known in Latin as Alpetragius an Arabic astronomer born in al-Andalus was a disciple of Ibn Tufail and a contemporary Ibn Rušd, who also presented a homocentric spheres model of astronomy, a development of the concept of Ibn Bājja and Ibn Tufail. He applies the impetus theory of John Philoponus to planetary motion. His Kitāb al-Hayʾah (The book of theoretical astronomy/cosmology) presented criticism of Ptolemaeus’ Almagest from a physical point of view.
Abu Jafar Ahmad ibn Yusuf ibn al‐Kammad (died 1195) was an Arabic astronomer born in Seville, whose works such as al Kawr ala al dawr, al Amad ala al abad, and al Muqtabas, which is a compilation of the two previous zijes were read throughout the Iberian Peninsula, and North Africa.
Abu Muhammad Abd al-Haqq al‐Ghafiqi al‐Ishbili, also known as Ibn al‐Hāʾim (fl. c. 1213) was another Arabic astronomer born in Seville, who wrote al‐Zīj al‐kāmil fī al‐talim (The Perfect Handbook on Mathematical Astronomy) a complete and accurate description of astronomy in al-Andalus.
It should be clear from the sketches above that medieval Islamicate culture presented a wide ranging and diverse dialogue on astronomy over a period of several centuries much of which as we shall see entered medieval Europe during the twelfth century Scientific Renaissance.