ASTRONOMY

In astronomy, Muslims continued the tradition of Ptolemy, while making extensive use of the knowledge of the Persians and Indians. The first astronomers of Islam, who flourished during the second half of the 2nd / 8th century in Baghdad, founded their astronomical works substantially on Persian and Indian astronomical tables. The most important astronomical work of pre-Islamic Persia that is preserved is the Tables of the king (Zīj-i Shāhī or Zīj-i Shahriyārī), composed around 555 AD, during the reign of the Sassanid king Anūshīrawān the Just, and founded themselves in much of it on the theories and astronomical practices of the Indians.
This work was for Sasanian astronomy what the Siddhānta were for the Indians and the Almagest for the Greeks; it had in the formation of Islamic astronomy the same important role of these last sources. This text - which possessed various distinctive characters, including setting the beginning of the day at midnight rather than midday, as was customary - was translated into Arabic by Abū'l-æasan al-Tamīmī, with a commentary of Abū Ma'shar (Albumasar), the most famous Muslim astrologer. The Zīj-i Shāhī were the basis of the astronomical activity of famous astronomers such as Ibn al-Naubakht and Māshā'allāh (Messala), who flourished during the reign of al-Manöūr, and who made a contribution to the preliminary calculations for the foundation of the city ​​of Baghdad. Along with some astrological treatises, in which the typically Sasanian emphasis on Jupiter-Saturn conjunctions was transmitted to the Muslims, the Zīj-i Shāhī represent the most important astronomical legacy of Persian sasanide, and the oldest foundation for the foundation of the Islamic astronomy.
With the first official astronomer of the Abbasids, Muáammad al-Fazārī, who died around the 161 / 777, direct Indian influence became dominant. In the 155 / 771 an Indian mission arrived in Baghdad to teach you the Indian sciences and to cooperate in the translation of texts in Arabic. A couple of years later the al-Fazārī zīj appeared, based on the Siddhānta of Brahmagupta. Al-Fazārī also composed various astronomical poems and was the first in Islam to build an astrolabe, which later became the typical instrument of Islamic astronomy. His main work, which became known as the Great Siddhānta, remained the sole basis of astronomical science until the time of al-Ma'mūn, in the third / ninth century.
Active in introducing Indian astronomy into Islam, he was a contemporary of al-Fazārī, Ya'qūb ibn Tariq, who studied under the guidance of an Indian master and became very expert in the field. Mainly through the efforts of these two men, more than all the others, Indian astronomy and mathematics were introduced into the current of Islamic science. Other works in Sanskrit, particularly the Siddhānta of Āryabhata, had a certain diffusion in this period, remaining, together with the already mentioned Persian works, the authoritative sources of astronomy up to the time of al-Ma'mūn, when they were translated into Greek Greek works.
Within the ample movement that took place under al-Ma'mūn to translate foreign works into Arabic, fundamental Greek astronomical texts became available, which substituted to some degree the Indian and Persian works that had monopolized the field until that period. The Almagest was translated several times, and the Tetrabiblos (Quadripartitum) and the astronomical tables of Ptolemy, known as Canones procheiroi, were also translated.
With these and other translations from the Greek and the Syriac the ground was prepared for the rise of Islamic astronomy, and in the third / ninth century some of the greatest figures of science appeared on the scene. The first part of the century was dominated by æabash al-æāsib, under whose direction the "ma'mūniche" tables were composed; from al-Khwārazmi, who, in addition to his important mathematical writings, left significant astronomical tables; and from Abū Ma'shar. The latter is the Muslim astrologer most often cited in the West, and his Introductorium magnum in astrologiam was translated and printed several times in Latin. Al-Farhānī (Alfragano), the author of the well-known Elements of astronomy, also belongs to the period of al-Ma'mūn.
In the second half of the III / IX century the study of astronomy continued its rapid course. Al-Nairīzī (Anarizio) commented on the Almagest and wrote the most complex treatise ever written in Arabic on the spherical astrolabe (or armilla). His contemporary Thābit ibn Qurrah (Tebizio) also played a leading role in the field of astronomy; he is particularly famous for having supported the theory of oscillatory motion of the equinoxes. To account for this trepidation, he added a ninth sphere to the eight of Ptolemaic astronomy, an innovation adopted by most of the later Muslim astronomers.
His compatriot al-Battānī (or Albategno), whom some authors consider the greatest Muslim astronomer, soon followed Thābit ibn Qurrah and continued his line of study, while repudiating the theory of trepidation. Al-Battānī made some of the most accurate observations in the annals of Islamic astronomy. He discovered the shift of the apogee of the Sun from the time of Ptolemy, observation that led him to the discovery of the motion of solar apsides. He determined the extent of the 54,5 precession '' per year, and the inclination of the ecliptic to 23 ° 35 '. He also discovered a new method for determining the time of the vision of the new Moon, and made a detailed study of solar and lunar eclipses, still used in the eighteenth century by Dunthorn in his determination of the gradual variation of the motion of the Moon. The main astronomical work of al-Battānī, which also contains a series of plates, became known in the West under the title De scientia stellarum; it remained one of the fundamental works of astronomy until the Renaissance. It is not surprising that his works have received, in the edition with translation and commentary by the famous Italian scholar CA Nallino, a study more attentive than the one dedicated to the works of any other Muslim astronomer in modern times.
Astronomical observation was carried out during the fourth / tenth century by figures like Abū Sahl al-Kūhī and 'Abd al-Raámā al-ūfī. The latter is particularly famous thanks to the Figures of the stars, which G. Sarton, the eminent historian of Islamic science, considers, together with the zij of Ibn Yunus and those of Ulugh Beg, one of the three greatest masterpieces of astronomy of observation in Islam. This book, which provides a chart of fixed stars with figures, was widely used both in the East and in the West; his manuscripts are among the most beautiful in medieval scientific literature. This period also includes Abū Sa'īd al-Sijzī, who was particularly noted for having built an astrolabe based on the motion of the Earth around the Sun, and the aforementioned Abū'l-Wafā 'al-Buzjānī, who, in addition to being among the most remarkable Muslim mathematicians, he was also an expert astronomer. He wrote a simplified version of the Almagest to facilitate the understanding of Ptolemy's work, and he spoke of the second part of the Moon's uprising in such a way as to induce the French scholar L. Am. Sillillot began a long controversy in the nineteenth century on the alleged discovery by Abū'l-Wafā 'of the third inequality of the Moon. In any case, current opinion tends to discredit this thesis, and to reconfirm Tycho Brahe as his discoverer.
Finally, we must mention, as one of Abū'l-Wafā's contemporaries, the Andalusian alchemist and astronomer Abū'l-Qāsim al Majrīøī, whose fame is linked above all to his hermetic and occultist writings. Al-Majrīøī was also a capable astronomer and wrote comments on the plates of Muhammad ibn Mūsā al-Khwārazmī and the Planisphaerium of Ptolemy, as well as a treatise on the astrolabe. Moreover, it was he and his disciple al-Kirmānī who made the Epistles of the Brothers of Purity known in Andalusia.
The 397th / 1007th century, which marks the apogee of activity in the Islamic sciences, also witnessed the work of various important astronomers, including al-Bīrūnī, whose determination of latitudes and longitudes, geodetic measurements and various important astronomical calculations make him one of the main figures in this field. Ibn Yūnus, who was the astronomer of the Fatimid court in Cairo, completed his Zīj (the Hākimite Tablets) in XNUMX/XNUMX, and thus made a lasting contribution to Islamic astronomy. These tables, in which many constants were carefully remeasured, are among the most accurate that were compiled during the Islamic period. Ibn Yūnus is considered for this reason by some historians of science, such as Sarton, perhaps the most important Muslim astronomer, regardless of the fact that he was a skilled mathematician, who solved spherical trigonometry problems by means of orthogonal projections and who was probably the first to study the isometric oscillatory motion of a pendulum - an investigation that later led to the construction of mechanical clocks.
At the second half of this century belongs the first eminent Spanish astronomer of observation, al-Zarqālī (Arzachel). He invented a new astronomical instrument called öaáīfah (Saphaea Arzachelis), which became very well known; he is also attributed the explicit demonstration of the motion of the apogee of the Sun with respect to fixed stars. Its most important contribution is constituted, however, by the publication of the Toledan Tables, composed with the help of various other Muslim and Jewish scientists, and widely used by both Latin and Muslim astronomers of later centuries.
Spanish astronomy after al-Zarqālī developed into an anti-systemic vein, in the sense that they began to be criticized against the theory of epicycles. In the 6th / 12th century he began to criticize the Ptolemaic planetary system Jābir ibn Aflāá, which in the West was known as "Geber" and was often mistaken for the famous alchemist. Also the philosophers Avempace and Ibn Tufail (known in the West as Abubacer) criticized Ptolemy. Avempace, under the influence of the Aristotelian cosmology, which was then beginning to become dominant in Andalusia, proposed a system based exclusively on eccentric circles; Ibn Tufail is considered the author of a theory that was developed more fully by one of his disciples of the VII / XIII century, al-Bitrūjī (Alpetragio). This was a complex system of homocentric spheres that was also called "spiral motion theory" because in his vision the planets seem to perform a sort of "spiral" movement. Although this new system did not present any advantage over the Ptolemaic, and could not supplant it, direct criticism of the Ptolemaic system from al-Bitrūjī and earlier astronomers was used by Renaissance astronomers as an effective tool against Ptolemy's old astronomy.
Even in the East a certain dissatisfaction with the Ptolemaic system went hand in hand with the astronomical work based on his theory. The Sanjarī Zīj, composed in the 6th / 12th century by al-Khāzinī, were followed by the Ilkhanid Tablets of the 7th / 13th centuries, which were the result of observations made in Maragha. But at the same time Naöir al-Dīn al-Tūsī, the most important astronomer of Maragha, also severely criticized Ptolemy. In his Memorial of astronomy, al-Tūsī clearly demonstrated his dissatisfaction with the Ptolemaic planetary theory. In fact, al-Tūsī proposed a new planetary model that was completed by his disciple Qutb al-Dīn al-Shīrāzī. This new model sought to be more faithful than the Ptolemaic model to the concept of the spherical nature of the heavens, placing the Earth in the geometric center of the celestial spheres and not at some distance from the center, as we find in Ptolemy. Al-Tūsī then conceived two spheres rotating one inside the other to explain the apparent motion of the planets.
This is why the American historian of Islamic mathematicians, ES Kennedy, who discovered this planetary model, designated it as the "pair of Al-Tūsī", since it represents the sum of two mobile vectors. Al-Tūsī intended to calculate the details of this model for all planets, but evidently did not complete this project. On his disciple Quøb al-Dīn al-Shīrāzī the task was to elaborate a variation of this model for Mercury, and on the damascene astronomer of the VIII / XIV century Ibn al-Shāøir to complete the lunar model in his Text of the investigation. final in the amendment of the elements. Ibn al-Shāøir, referring to the model of Al-Tūsī, did without the eccentric deferent of Ptolemy and introduced a second epicycle in the solar and lunar systems. The lunar theory proposed two centuries later by Copernicus is the same as Ibn al-Shāøir, and it seems that Copernicus was somehow aware of this late development of Islamic astronomy, perhaps through a Byzantine tradition. All that is astronomically new in Copernicus can be found substantially in the school of al-ßūsī and his disciples.
The tradition of Maragha was continued by the direct disciples of al-Tūsī, such as Quøb al-Dīn al-Shīrāzī and Muáyī al-Dīn al-Maghribī, as well as by the astronomers gathered by Ulugh Beg in Samarkand, as Ghiyāth al-Dīn al-Kāshānī and Qūshchī. It survived even to modern times in various regions of the Islamic world, such as northern India, Persia and, to a certain extent, Morocco. Many comments were made on earlier works, such as the commentary on the Qūshchī treaty on astronomy, by 'Abd al-æayy Lārī in the eleventh / seventeenth century, which was popular in Persia up until modern times.
This later tradition of Islamic astronomy continued to correct the mathematical shortcomings of the Ptolemaic model, but it did not break the boundaries of the closed Ptolemaic universe, which was so intimately connected to the medieval worldview. It is true that many of the later medieval astronomers criticized various aspects of Ptolemaic astronomy. It is also certain that astronomers such as al-Bīrūnī knew the possibility of the motion of the Earth around the Sun and even - as al-Bīrūnī proposed in his letters to Avicenna - the possibility of an elliptical rather than circular motion of the planets. However, none of them took, nor could, take the step of breaking with the traditional world view, as would have happened in the West in the Renaissance - because such a decision would have meant not only a revolution in astronomy, but also an upheaval in the religious sectors. , philosophical and social. The influence of the astronomical revolution on the mind of man cannot be overestimated. As long as the hierarchy of knowledge remained intact in Islam, and scientia continued to be cultivated within the sapientia, a certain "limitation" in the physical domain was accepted in order to preserve the freedom of expansion and realization in the spiritual domain. The wall of the cosmos was preserved in order to protect the symbolic meaning that such a walled view of the cosmos held for most of humanity. It was as if the ancient scientists and scholars predicted that the collapse of that wall would also destroy the symbolic content of the cosmos, and even erase the meaning of the "cosmos" (lit. order) for the great majority of men, for whom it is difficult conceive the sky as incandescent matter that swirls in space and at the same time as the Throne of God. Thus, despite all the technical possibility, the step towards breaking the traditional vision of the world was not taken, and Muslims were content to develop and perfecting the astronomical system which they had inherited from the Greeks, Indians and Persians, and which had been fully integrated into the Islamic worldview.
The various new features of Islamic astronomy include, in addition to all the improvements made to the Ptolemaic system, the stellar catalog of Ulugh Beg, which was the first new catalog from the time of Ptolemy, and the replacement of the calculation of the strings with the calculation of breasts and with trigonometry. The Muslim astronomers also modified the general system of the Alexandrians in two important aspects. The first modification consisted in abolishing the eight spheres that Ptolemy had hypothesized to communicate the diurnal motion to each sky; the Muslims replaced a single starless sky at the edge of the universe, above the sky of the fixed stars, which in carrying out its daytime rotation carries all the other heavens with it. The second modification, which was of greater importance to the philosophy of the sciences, implied a change in the nature of the heavens. Among the many problems of astronomy, those that were particularly interesting for Muslim astronomers concerned the nature of the celestial bodies, the planetary motion and the distance and size of the planets, which were connected with calculations based on the mathematical models with which they operated. They obviously had a great interest in descriptive astronomy, as their new stellar catalogs and the new observations of the skies demonstrate.
It is well known that, in the Almagest, Ptolemy had dealt with the celestial spheres as purely geometrical forms, hypothesized in order to "save the phenomena". He therefore followed the tradition of Greek mathematical astronomers, who were not so much interested in the ultimate nature of the heavens, but in the means of describing their motions according to mathematical laws. The Muslims, reacting against this point of view, proceeded to "solidify" the Ptolemaic skies, in accordance with the "realistic" perspective of the Muslim mentality and, following trends already present in the hypotheses on the planets, sometimes attributed this concept to Ptolemy himself. Muslims have always considered the role of natural science in the discovery of those aspects of Reality represented in physical existence, rather than the creation of mental constructs to impose upon Nature, without having a necessary correspondence with the various aspects of Reality. The solidification of the abstract Ptolemaic skies thus represents a profound transformation of the meaning and role of the mathematical sciences in their relationship with Nature, a fundamental problem for the philosophy of the sciences.
The tendency towards the "physical" interpretation of the heavens was already evident in the writings of the astronomer and mathematician of the third / ninth century, Thābit ibn Qurrah, and especially in his treatise on the constitution of the heavens. Although the original of this treatise has apparently been lost, quotations in the works of many later authors, including Maimonides and Albertus Magnus, indicate that Thābit ibn Qurrah had conceived the heavens as solid spheres, with a compressible fluid interposed between the orbs and eccentrics.
This process of transforming the abstract skies of the Greeks into solid bodies was carried out by Alhazen, who is more famous for his studies in optics than for his studies in astronomy. In his Compendium of Astronomy (although the Arabic original has been lost, versions in Hebrew and Latin remain), Alhazen describes the motion of the planets not only in terms of eccentrics and epicycles, but also according to a physical model that exerted a great influence on the Christian world up to the time of Kepler. It is curious, however, that Muslim philosophers and scientists did not generally recognize, it seems, the implications of this solidification of the Ptolemaic skies. Andalusian Peripatetics, such as Ibn Tufail and Averroes, continued to attack Ptolemaic astronomy in the name of Aristotelian physics, neglecting to consider Alhazen's work as well - perhaps because, as Duhem suggests, it would have weakened their reasoning. However, with the Spanish translation of the Treaty of Alhazen, following the directive of Alfonso the Savio, the work instead became a tool of Ptolemy's Latin supporters in their defense against attacks by the Peripatetics. Even in the Muslim world it was now regarded with favor by astronomers; three centuries later Nāsī al-Dīn al-Tūsī would have composed a treatise on the heavens based on the Compendium of Alhazen and following his ideas very closely.
Almost all Muslim astronomers, and especially those who dealt with mathematical astronomy, faced the problem of planetary motions. Few, however, treated him with such depth and rigor as al-Bīrūnī. We have already had occasion to mention the name of al-Bīrūnī as one of the most universal Muslim scientists and scholars. In astronomy, as well as in physics and history, he made many leading contributions. His Canon of al-Mas'ūdī is the most important Muslim astronomical encyclopedia; it deals with astronomy, astronomical geography and cartography, and various branches of mathematics, drawing on the writings of the Greeks, Indians, Babylonians and Persians, as well as previous Muslim authors, and also on its own observations and measurements . If his work had been translated into Latin it would certainly have become famous as the Canon of Avicenna. Writing around the same time as Alhazen, al-Bīrūnī described the motion of the planets in the manner of Ptolemy, putting the system of eccentrics and epicycles into that very complex form for which medieval astronomy has become famous. This astronomical encyclopedia is the best proof of the mental processes of the Muslim astronomical scientist, when he tried to decipher the complex planetary motions in terms of the Pythagorean circles - on the one hand by transforming the abstract geometric figures of the Greeks into concrete spheres, on the other by preserving idea of ​​celestial harmony which had deeply imbued the spirit of the Greek Gnostics, especially of the school of Pythagoras.
Another problem that occupied a central position in Muslim astronomy was that of the size of the cosmos and planets. Of the various attempts made by Muslim astronomers to determine the distances and sizes of planets, none became as well known as that of al-Farghānī, the XNUMXrd / XNUMXth century Transoxiana astronomer. His Elements of Astronomy (Rudimenta astronomica) were translated into Latin, and the distances given in them were universally accepted in the West until the time of Copernicus. In determining the distances of the planets, al-Farghānī followed the theory that in the universe there is no "wasted space" - that is, that the apogee of one planet is tangent to the perigee of the next. The distances given by al-Farghānī for the apogee and perigee of each planet in the epicyclic system correspond to the eccentricities of the ellipses in modern astronomy.