The translation activities in the Bayt al-Hikma gave rise to a new Arabic science that spread from Baghdad eastward to Central Asia and eventually westward to Africa and Spain, as the equivalent of the Islamic renaissance spread to many of the lands conquered by the Prophet Muhammed’s followers.
Astronomy held pride of place among the sciences in many Islamic regions (though for those with a philosophical bent, divine science was more revered), and Arabic astronomers often waxed eloquent in extolling the utility and godliness of their field. Muhammed ibn Jabir al-Battani (ca 850–929) begins his astronomical tables by citing verses of the Qu’ran in praise of astronomy.
Verily, in the creation of the heavens and of the earth, and in the succession of the night and of the day, are marvels and signs for men of understanding heart (iii, 187); Blessed be He who has placed in the heaven the signs of the zodiac, who has placed in it the lamp of the sun and the light-giving moon (xxv, 62); It is He who appointed the sun for brightness and the moon for a light, and has ordained her stages, that you may learn the number of the years, and the reckoning of time (x, 5).
According to Aydın Sayılı, the first observatories in Islam were founded by Caliph al-Ma’mun, who in 828 built one at Shammasiya in Baghdad and another at the Dayr Murran monastery on Mount Qasiyun near Damascus. The two most prominent figures associated with the Shammasiya observatory were al-Khwarizmi and Yahya ibn Abi Mansur, who is referred to by the eleventh-century historian Sa’id al-Andalusi as ‘the senior of the astronomers of his age’. Both al-Khwarizmi and Ibn Abi Mansur worked at the Bayt al-Hikma, which has led some scholars to infer that the Shammasiya observatory was associated with the House of Wisdom.
The eleventh-century astronomer and polymath al-Biruni says that Ibn Abi Mansur and al-Khwarizmi made daily solar and lunar observations at the Shammasiya observatory in the years 828–9, including a determination of the autumnal equinox. He notes that similar observations were also made at the same time at Qasiyun, and that the two sets of measurements of the autumnal equinox were compared, taking into account the eight degree difference in longitude between Damascus and Baghdad.
Ibn Abi Mansur died in 829 and al-Mam’un appointed Khalid ibn ‘Abd al-Malik al-Marwarudhi to head the observatory at Damascus and to prepare a zij, or an astronomical handbook with tables. According to the astronomer Habash al- Hasib (d. ca. 865): ‘Al Ma’mun ordered him [Khalid] to make ready instruments of the greatest possible perfection and to observe the heavenly bodies for a whole year at Dayr Murran. Khalid did this and thereby attained to the truth concerning the positions of the sun and the moon across the heavens.’
The instruments used at the Shammasiya and Qasiyun observatories included astrolabes, gnomons, mural quadrants, azimuthal quadrants and armillary spheres. The Egyptian astronomer Ibn Yunus says that after the death of Ibn Abi Mansur his armillary sphere was sold at the Paper Maker’s Market in Baghdad. Other sources reveal that the astronomers at the Shammasiya and Qasiyun observatories studied the motions of the planets along with those of the sun and moon, as well as measuring the obliquity of the ecliptic, the rate of precession of the equinoxes, and the length of the tropical year, the time between two spring or autumn equinoxes. Another astronomical activity sponsored by al-Ma’mun was the measurement of the latitude and longitude of Baghdad and Mecca in order to determine the direction or qibleh of Mecca from Baghdad. This was done by simultaneous observations of lunar eclipses at Baghdad and Mecca, the distance between the two cities having been measured by al-Ma’mun’s surveyors.
According to Habash al-Hasib, the early Islamic astronomers at Baghdad and Damascus based their work on what they had learned from the Greek astronomers, particularly Ptolemy, and their observations were made to correct whatever errors there might be in the ancient astronomical tables and bring them up to date.
The first of the new Islamic scientists in the generation after the founding of the Bayt al-Hikma was the astronomer Muhammed al-Battani. Al-Battani was from Harran, the birthplace of Thabit ibn Qurra, his older contemporary. He too was of Sabean origin, but unlike Thabit he became a Muslim, as indicated by his first name. His date of birth is unknown, but since his earliest recorded astronomical observation was made in 877 it has been suggested that he was born before 858. This information is from the History of Learned Men by Ibn al-Qifti (d. 1248), who says that al-Battani ‘composed an important zij containing his own observations of the two luminaries [sun and moon] and an emendation of their motions as given in Ptolemy’s Almagest’.
Ibn al-Qifti goes on to say that al-Battani continued to make observations until 918 and that he died in 929. The zij that he refers to are the Sabean Tables (al-Zij al-Sabi), known in its Latin translation by Plato of Tivoli in the first half of the twelfth century as the Opus astronomicum, where the author’s name is given as Albategnius.
The instruments known to have been used by al-Battani are an astrolabe, a gnomon, an armillary sphere, a parallactic ruler, which he calls ‘the long alidade’, and a mural quadrant, which he equipped with an alidade, according to al-Biruni. Al-Battani mentions the latter instruments in connection with his measurements of the obliquity of the ecliptic: ‘We have observed it in this time of ours with the parallactic ruler and the mural quadrant...after having made their divisions very precise and securing them in their place as carefully as possible.’
Al-Battani’s theoretical astronomy is derived almost entirely from Ptolemy and from his immediate Arabic predecessors. His most important contributions are his accurate observations, particularly concerning the variation of the apparent sizes of the sun and moon, the difference being most apparent in annular solar eclipses, when the moon’s apparent diameter is a minimum.
The Sabean Tables were used by Copernicus, who refers to ‘al-Battani the Harranite’ in discussing the orbits of Mercury and Venus. Copernicus makes a number of other references to al-Battani, most notably his measurement of the sidereal year, which he compared to his own values as well as Ptolemy’s and the one he attributed to Thabit ibn Qurra.
The sixteenth-century Danish astronomer Tycho Brahe also referred to al-Battani’s observations, as did Kepler and Galileo. The definitive Latin translation of the Sabean Tables was published by the Italian orientalist C. A. Nallino, more than a thousand years after the Arabic original had been written.
Al-Battani’s younger contemporary, the astronomer and mathematician Abu Ja’far al-Khazin, was also a Sabean, of Persian origin, perhaps from Khorasan province in eastern Iran, though this has never been proven. He spent part of his life at the court of the Buwahid emir Rukn al-Dawlah (r. 932–76) at Rayy, where in 960 he made his last known observation, a measurement of the obliquity of the ecliptic. He is presumed to have died at Rayy in the following decade.
Al-Khazin is credited with twelve works in astronomy and eleven in mathematics. All that survives of his astronomical writings are nine extant mathematical texts, one complete astronomical text and fragments of his tables, while his Commentary of the Almagest appears not to have survived. This latter seems to have been an important work, as evidenced by references to it by later Islamic scholars, most notably al-Biruni. One of his lost works, the Book on the Secret of the Worlds, first mentioned in the seventeenth century, could have been a new world model based on Ptolemy’s Planetary Hypotheses, which would be used a century later by Ibn al-Haytham in his criticism of certain elements of the Ptolemaic system.
One of al-Khazin’s mathematical works – which is preserved in Oxford – is a treatise on the impossibility of solving equations of the type x3 + y3 = z3. This is a special case of what came to be known as Fermat’s Last Theorem, written by the French mathematician Pierre de Fermat ca. 1637, i.e., ‘It is impossible for a cube to be written as the sum of two cubes or a fourth power to be written as the sum of two fourth powers, or in general for any number which is a power greater than the second to be written as a sum of two like powers.’ Fermat wrote this statement in the margin of a copy of the Arithmetica by Diophantus, followed by an additional comment noting that ‘I have a truly marvelous demonstration of this proposition which this margin is too narrow to contain.’ But Fermat never supplied the proof, which eluded many of the world’s great mathematicians for more than three and one-half centuries. The problem was finally solved by Andrew Wiles, a British mathematician working at Princeton, who in May 1995 published his proof of Fermat’s Last Theorem in the Annals of Mathematics. The books and articles written on this great discovery mention the succession of famous mathematicians who worked on this problem over the course of two millennia, from Diophantus to Fermat to Wiles, but there was not a single mention of al-Khazin, whose pioneering work on this subject has been irretrievably lost.
The Persian astronomer ‘Abd al-Rahman al-Sufi (903–86) was known in the West as Azophi. Little is known of his life and career except his association with the Amir al-Umara, who captured Baghdad in 945 and for more than a century afterwards acted as protectors of the ‘Abbasid caliphs, reducing them to the role of mere puppets. He worked in Shiraz as court astronomer of ‘Adud al-Dawlah (r. 949–82), for whom he determined the obliquity of the ecliptic by observing the winter and summer solstices in the years 969–70.
Al-Sufi is credited with five works in astronomy and one in mathematics. He is best known for his Treatise on the Constellations of the Fixed Stars. This is a critical revision of Ptolemy’s star catalogue, based on at least some of his own observations, which became a classic of Arabic astronomy for many centuries afterwards and later became known to the West through a Castilian translation.
The old Arabic star names that he used were adopted by most later Islamic astronomers and have made their way into modern stellar terminology. The illuminated manuscripts of the Treatise are among the most beautiful in Islamic science. The paintings show forty-eight constellations, with tables giving the position, magnitudes and colours of all of the stars. Each of the constellations is shown in two facing views, one as it would look to an observer on earth, the other as it would appear on the celestial sphere to a viewer outside. The mythological figures are shown in varying cultural costumes – mostly Central Asian, but some Buddhist and Chinese in the older manuscripts with later manuscripts showing them in dress that accords with the style of the period – so that in the constellation that bears his name Perseus is dressed in a flowing Arabic robe, as he brandishes his sword in one hand and with the other holds the severed head of Medusa by her long hair.
The most outstanding Islamic physician in the latter half of the tenth century was Ali ibn al-Abbas al-Majusi (c. 925–94), the Latin Haly Abbas. Majusi means ‘Zoroastrian’, although he himself was a Muslim, born near Shiraz (though some sources say it was Ahvaz). He received his medical training under the physician Abu Mahir ibn Sayyar, after which he directed the Baghdad hospital named for ‘Adud al-Dawlah (d. 983), to whom he dedicated his only medical treatise, the Kitab al-Maliki (The Royal Book), known in its Latin translation as Liber regius. The main interest of this book today is al-Majusi’s assessment of his Greek and Arabic predecessors, including al-Razi.
The Kitab al-Maliki consists of twenty chapters, evenly divided between the theory and practice of medicine. His surprisingly accurate description of pleurisy and its symptoms is evidence of the state of Islamic medicine at the time: ‘Pleurisy is an inflamation of the pleura, with exudation which pours materials over the pleura from the head or chest...Following are the four symptoms that always accompany pleurisy: fever, coughing, pricking in the side, and difficult breathing.’
Al-Majusi stressed the importance of proper diet, bathing, rest and exercise for a healthy body and mind, and he wrote on the relationship between psychology and medicine. He emphasised the importance of psychotherapy in treating psychosomatic illnesses, one of which he recognised as unrequited love. His writings on poisons, including their symptoms and antidotes, represents the beginning of medieval toxicology. He wrote on the use of opiates and problems of drug addiction as part of his general discussion of medicines, and he also emphasised chemotherapy. He opposed contraception, as well as the use of drugs to induce abortion except when the physical or mental health of the mother was endangered. Here and in other medical issues he urged physicians and medical students to uphold the highest standards of medical ethics, as stated in the Hippocratic oath.
Abu’l Wafa al-Buzjani was born in 940 in Buzjan, now in Iran, and in 959 he moved to Baghdad, where he remained for the rest of his life, passing away there in 997 or 998. He made observations at the Baghdad observatory and wrote two astronomical treatises, the most important of which is his Kitab al-Majisti. Buzjani’s choice of title reflects the importance of spherical trigonometry for mathematical astronomy, the subject of The Almagest. His main contribution in this work is his improvement in the trigonometric tables used in astronomy, achieved through his methods for approximating the sine function and solving problems in spherical trigonometry. He was also a major figure in the introduction of the sine theorem of spherical trigonometry.
Abu’l Wafa is credited with thirteen treatises on mathematics, including commentaries on Euclid, Diophantus, Hipparchus and al-Khwarizmi, though we know nothing of their actual content. Two of his original works are treatises on applied mathematics, entitled A Book about What is Necessary for Scribes, Dealers, and Others from the Science of Arithmetic and A Book about what is Needed by Artisans for Geometric Constructions. He also wrote two books on musical theory, one of them a revision of Euclid’s work on music and the other a Treatise on Rhythms. Abu’l Wafa has been honoured by giving his name to a crater on the moon.
Abu’l Wafa’s best known student was Abu Nasr Mansur ibn Iraq, who in turn was the teacher of the famous al-Biruni. Abu Nasr was born in the second half of the tenth century in Khwarazm, and belonged to the Banu ‘Iraq family who ruled that region until it was conquered by the Ma’muni dynasty in 995. He spent most of his life in the service of two successive emirs of that dynasty, ‘Ali ibn Ma’mun and Abu’l-‘Abbas Ma’mun, who supported a number of other scientists, including al-Biruni and Ibn Sina. When Abu’l-‘Abbas Ma’mun died, ca. 1016, Abu Nasr and al-Biruni were captured by the Ghaznavids and taken as prisoners to the court of Sultan Mahmud al-Ghaznawi in Ghazna (now Ghazni in Afghanistan). Abu Nasr spent the rest of his days in Ghazna, passing away there ca. 1036.
Abu Nasr is credited with 30 works, 11 of them in mathematics and 19 in astronomy. His most important discovery in mathematics, which he shares with Abu’l Wafa, is the sine law in trigonometry. The most important of Abu Nasr’s extant writings is his Improvement of the Spherics of Menelaus. However, the most complete Arabic version of that work was produced by Tusi, who brought together several different translations.
Abu Rayhan al-Biruni was born in 973 at Kath on the Oxus, one of the two old capitals of Khwarazm, presently the town of Beruni named for him in Uzbekistan. Al-Biruni was very young when he began his studies with Abu Nasr, and he was only seventeen when he made his first recorded astronomical observation, a measurement of the meridian solar altitude at Kath, from which he computed its terrestrial latitude. Five years later he made an observation of the summer solstice near Kath, but then he was caught up in the civil war that erupted in Khwarazm, and had to flee the country for a time. He refers to this disturbance in his Tahdid nihayat al-amakin, or The Determination of the Coordinates of Cities: ‘After I had barely settled down for a few years I was permitted by the Lord of Time to go back home, but I was compelled to participate in worldly affairs, which excited the envy of fools, but which made the wise pity me.’
Al-Biruni was back in Kath by 997, for on 24 May of that year he observed a lunar eclipse there. Abu’l Wafa observed the same eclipse from Baghdad, and by noting the difference in time of the two observations they were able to compute the difference in longitude between the two places.
Around the year 1000 al-Biruni went to Gurgan at the south-east corner of the Caspian Sea, where the Ziyarid ruler Qabus had re-established himself. Al-Biruni dedicated to Qabus his earliest extant major work, the Chronology. There he refers to seven other works that he had already written, none of which have survived. The titles of these lost treatises indicate that al-Biruni had already begun researches in fields in which he would do much of his later studies, for five of these works were in astronomy and astrology, two on history and one on mathematics.
During the year 1003 al-Biruni observed two lunar eclipses in Gurgan, one on 19 February and the other on 14 August. Then the following year he observed a lunar eclipse in Jurjaniyye, at that time ruled by the emir Abu’l-‘Abbas Ma’mun brother-in-law of the powerful Turkish sultan Mahmud al-Ghaznawi of Ghazna, in what is now Afghanistan. As he notes in his Tahdid, al-Biruni was deeply involved in Khwarazmian political affairs, particularly in the delicate negotiations between Abu’l-‘Abbas Ma’mun and Sultan Mahmud. Mahmud conquered Khwarazm in 1017 and executed Abu’l-‘Abbas Ma’mun, after which al-Biruni was exiled to the village of Lamghan north of Kabul, where he recorded a solar eclipse on 14 October 1018. Later he entered the service of Sultan Mahmud as court astronomer and astrologer, accompanying him on campaigns that conquered most of the small Persian kingdoms in the region and expanded the Ghaznavid domains well into the Indian subcontinent.
The knowledge that al-Biruni obtained in these campaigns enabled him to write his major work, in its abbreviated version titled the Tahqiq ma li’l Hind min Maqalatin, or A Verification of What is Said on India, known in its English translation as Alberuni’s India. He also met and questioned emissaries sent to Sultan Mahmud’s court from the Volga Turks, Uighur Turks and the Chinese, from whom he obtained geographical and other information on Central Asia and the Far East.
Sultan Mahmud died in 1030 and was succeeded by his son Mas’ud. Two years later Mas’ud was assassinated in a coup that brought to the throne his son Mawdud, who reigned until his death in 1050. Al-Biruni enjoyed the patronage of all three sultans, outliving Mawdud by a few months.
Based on his own bibliography, al-Biruni is credited with 146 works, of which 22 are extant. His works include 39 on astronomy, 23 on astrology, 16 on literature, 15 on mathematics, 10 on geodesy and mapping theory, 9 on geography, 5 on chronology, 4 on history, 3 on religion and philosophy, 2 on time measurement, 2 on mechanics, 2 on medicine and pharmacology, 2 on mineralogy and gems, 2 on magic, 2 on India, 1 on meteorology, and 9 on a variety of other subjects, including detailed descriptions of his observational instruments and inventions.
Al-Biruni’s native tongue was Khwarizmian, an Iranian language with no scientific vocabulary, and, through the languages of the courts, religion, literature and science, he learned both Arabic and Persian. He also acquired sufficient knowledge of Greek, Syriac and Hebrew to use dictionaries in those languages. His knowledge of Sanskrit was such that, with the aid of scholars from India, he was able to translate Indian scientific works into Arabic. His Arabic was so fluent that he was able to compose poetry in that language and to quote from the classics in his treatises.
A survey of al-Biruni’s extant works reveals the enormous range of his interests and the originality of some of his researches, his accomplishments placing him in the uppermost rank among all scientists.
His work on the Chronology of Ancient Nations is divided into twenty-one chapters, of which the first deals with the various definitions of the solar day and the second with the several ways of defining the year – solar (i.e. by the cycle of seasons), lunar, lunar-solar, Julian, Persian – as well as the notion of intercalation, i.e., adding extra days to the lunar calendar to make it compatible with the solar year. The last section of the book is on stereographic projection and other methods of mapping a sphere on to a plane, as done in the astrolabe.
Al-Biruni’s short thesis On the Astrolabe is considered to be the most useful work of its kind. His even briefer thesis on the sextant describes the giant mural sextant built at Rayy by the astronomer al-Khujandi for the emir Fakhr al-Dawlah, which al-Biruni may have inspected. The Tahdid nihayat al-amakin describes al-Biruni’s measurements of the geographical coordinates of cities through astronomical and terrestrial observations. He applied his method to determine the difference in longitude between Baghdad and Ghazna, his final result being in error by only eighteen minutes of arc.
Al-Biruni’s Book on the Multitude of Knowledge of Precious Stones is a study of the physical properties of various solids and liquids, including precious and semi-precious stones, whose specific gravities he measured using an ingenious balance based on Archimedes’ principle. He also writes of the medical properties of these materials and their philological and philosophical significance.
The first three of the thirty chapters in the treatise On Shadows include a philosophical discussion of gnomonics, the study of shadows cast by gnomons, as well as studies of the nature of light, shade and reflection, along with references to shadows in Arabic poems. The remaining chapters describe the use of the gnomon in determining the seasons of the year, the time of day, Muslim prayer times, the cardinal directions, the qibleh and the determination of heights of objects as well as terrestrial and celestial distances. The mathematical background of the gnomon is analysed as well as its use in sun-dials of various types.
The Canon of Al-Mas’udi is the most comprehensive of al-Biruni’s extant astronomical works, with more observational information and mathematical derivations than in the typical zij, along with detailed numerical tables designed to solve all of the problems encountered by a professional astronomer or astrologer. It is organised into eleven sections, the first two of which deal with general cosmological principles, most notably that the earth is the stationary centre of the hierarchical universe. Sections 3 and 4 deal with plane and spherical trigonometry, including tables of the trigonometric functions that are more precise than in other works available at that time; section 5 repeats much of the material in the Tahdid, covering geodesy and mathematical geography, with a table of geographic coordinates of cities and other places; sections 6 and 7 are on the sun and moon, respectively, using essentially Ptolemaic models but with many of the observations by al-Biruni himself; section 8 computes lunar and solar eclipses and the times of first visibility of the lunar crescent; section 9 includes a table with the coordinates of 1,029 stars, slightly more than in Ptolemy’s Almagest; section 10 is on the planets, with tables of their celestial coordinates, visibility and ‘stations’, i.e., where they begin and end their retrograde motion; and section 11 deals with the astronomical background of astrology.
The Kitab al-tafhim, known in its English translation as Elements of Astrology, became a well-known Islamic text of instruction in astrology, with Arabic and Persian versions both possibly translated in al-Biruni’s lifetime. Nevertheless, al-Biruni emphasised that he did not really believe in astrology, for he thought that the ‘decrees of the stars’ had no place in the exact sciences. In the final chapter al-Biruni discusses the movements of the planets in great detail, using the epicycle theory to explain their retrograde motion.
Another of al-Biruni’s extant astrological works is his treatise On Transits. The term ‘transit’ is used when one planet passes one another in the celestial sphere, an event that was believed to have astrological significance in Indian and Persian cosmologies, as evidenced by references to lost works in al-Biruni’s treatise.
Al-Biruni’s treatise On Pharmacology consists of 720 articles on drugs, most of which are identified by their names in Arabic, Greek, Syriac, Persian and an Indian language, and sometimes also in Hebrew or in less common languages or dialects such as Khwarizmian. Each drug is described along with its places of origin and its therapeutic properties, with the sources of information fully documented by al-Biruni, who disclaims his own medical competence on the subject.
Al-Biruni’s Kitab al Jamahir fi ma_rifat al-Jawahir (Book of the Multitudes, On the knowledge of Gems) is divided into two parts, with the first devoted to precious and semiprecious stones, the second to metals, where he uses other Arabic sources along with his own translations. The various materials are described, along with their principal sources. The weights of the metals are given relative to gold, and the prices of pearls and emeralds are tabulated in terms of their size. The book also contains observations on technological processes such as the casting of iron, the production of steel, and the mining and purification of gold.
Arguably Al-Biruni’s most famous work today is his monumental treatise on India, running to 656 pages in its English translation, whose subtitle describes it as An account of the religion, philosophy, geography, chronology, customs, laws and astrology of India. Al-Biruni says at the end of his book that the background information he has provided ‘will be sufficient for any one [in Islam] who wants to converse with the Hindus, and to discuss with them questions of religion, science, or literature, on the very basis of their own civilisation’.
Chapter 26 is ‘On the shape of Heaven and Earth according to the Hindu astronomers’. The most interesting part of this chapter is its last section, where al-Biruni discusses the possibility, raised by the Indian astronomer Brahmagupta, that the Earth rotates on its axis while the heavens remain at rest, as opposed to an older view that the Earth is stationary and the celestial sphere rotates about it. Al-Biruni refers to a book, now lost, that he himself wrote on the possible rotation of the earth, which he appears to have rejected.
Some of al-Biruni’s most interesting ideas are preserved in his question and answer correspondence with Ibn Sina, which took place around the year 1000. Here al-Biruni criticised many of Aristotle’s theories, such as the impossibility of a vacuum, while Ibn Sina defended them. Al-Biruni’s speculations about celestial motion are particularly interesting, for he disagrees with Aristotle’s doctrine of natural place and natural motion, proposing instead that the heavenly bodies do have gravity (i.e., weight) despite the fact that they move in circular orbits rather than toward the centre. He even seems to suggest that the heavens could have an elliptical motion without contradicting the laws of physics.
Al-Biruni’s other accomplishments include a calculation of the earth’s circumference, a geared calendar showing the motion of the sun and moon among the signs of the zodiac, a device for making accurate measurements of the specific gravities of liquids, a mechanical triangulation instrument for measuring distances such as the width of a river or the height of a minaret, and a mathematical method for determining the direction of Mecca from any point. But al-Biruni’s works were never translated into Latin, and though he was extremely influential in the Islamic world and though there was some knowledge of him in al-Andalus he had little influence on the subsequent development of science in Europe.
Al-Biruni, who personally spread Muslim knowledge of the world as far as Central Asia and India, writes in his Tahdid of the universal character of Islam and its role in uniting many peoples in its embrace. ‘And now Islam has appeared in the Eastern and Western parts of the world and has spread between Andalus in the West and parts of China and Central India in the East, and between Abyssinia and Nubia in the South and the Turks and Slavs in the North. It has, as never before, united the different nations in one bond of love...’