The Study of Astronomy
During the medieval period, scientists in the Islamic world made many contributions to the field of astronomy. While their work was based on ancient sources from Greece, Iran, and India, they updated methods for measuring and calculating the movement of heavenly bodies, and continued to develop models of the universe and the movements of the planets within it. Between the eighth and tenth centuries, Baghdad was a major center of study under the Abbasid caliphs al-Mansur (r. 754–75) and al-Ma’mun (r. 813–33), but local rulers across the region, in Cairo, Rayy, Isfahan, and other cities, also supported scientific research.
At this time, scientists translated studies in Sanskrit, Pahlavi, and Greek into Arabic, and, for the first time, recorded Arab Bedouin traditions. The Indian Sanskrit and Persian Pahlavi sources taught medieval astronomers methods for calculating the position of heavenly bodies, and for creating tables recording the movement of the sun, the moon, and the five known planets. The Bedouin traditions contained knowledge on the fixed stars, the passage of the sun and moon through the zodiacal signs and lunar mansions, and the seasons and associated phenomenon. This body of knowledge was refined in part because of the specific requirements of Islam; the religion required the ability to correctly determine the time and direction of Mecca for prayer, the moment of sunrise and sunset for fasting during Ramadan, and for fixing the appearance of the moon that marked the start of a new month. This led to the refinement of scientific instruments, an improvement in methods for making observations, and the creation of new calendrical systems.
Another branch of research was led by astronomers interested in a more accurate understanding of the planets’ movements, in response to Greek inquiries into this field. The most influential Greek texts were more concerned with creating a model of the universe and the movement of the heavenly bodies within it, but the literature proposed two very different approaches to this problem. On the one hand, Aristotle’s (384–322 B.C.) model of the universe, with the earth at its center, and the sun, moon, planets, and fixed stars rotating around it within uniformly turning spheres, was widely accepted. On the other hand, the work of Ptolemy (85–165 A.D.) sought a purely theoretical, geometrical representation of the universe based on precise observations, even if this conflicted with the ideal Aristotelian model of planets and stars.
Between the ninth and eleventh centuries, Islamic astronomers focused on criticizing and improving the geometrical models of Ptolemy. ‘Abd al-Rahman al-Sufi (903–986) was one of the most important scientists doing this work, supported by the Buyid sultan ‘Adud al-Daula, to whom he dedicated his Book of the Images of the Fixed Stars . This treatise describes the forty-eight constellations formed by what were called the “fixed stars” (the celestial objects that did not seem to move in relation to the other stars). It was written in Arabic, the language in which most scientists of the Islamic world worked, and was based on a series of new observations made by al-Sufi at Isfahan, the city in central Iran. Other important scientists of the time include al-Biruni (973–1048), who wrote al-Qanun al-Mas‘udi, dedicated to Sultan Mas‘ud of Ghazna, on the topics of astronomy and solar, lunar, and planetary motions; and Ibn al-Haytham (known in Europe as Alhazen, died 1039), who measured the thickness of the atmosphere and its effect on astronomical observations.
The Study of Astrology
Astrology seeks to predict the influence of the heavenly bodies on events on earth, relying on understanding the movement of the planets and the ability to calculate their positions in the future. In this way, astrology was considered a branch of astronomy, and serious scientists such as Abu Ma‘shar al-Balkhi (787–886), al-Biruni, and Nasir al-Din al-Tusi (1201–1274) all wrote astrological treatises. The number of medieval theologians, jurists, and philosophers who wrote anti-astrology tracts, however, indicates that it was controversial and not universally accepted as a scientific or ethical practice. Many believed it was against the tenets of Islam to suggest that forces other than God could determine human events.
This did not stop the practice of astrology—in fact, astrologers offered their services in bazaars, where anyone could pay for horoscope readings and predictions; and they were employed at royal courts, to help rulers decide such matters as when to announce an heir or launch a military campaign, or to predict the future state of their kingdoms. Horoscopes were also devised at the foundation of capital cities, such as Baghdad, capital of the Abbasids, and al-Mahdiyya, capital of the Fatimids, to foretell their futures.
The three tools of the astrologer were the astrolabe, used to determine the time by measuring the altitude of the sun or any visible stellar object ; the ephemeris, a table that gives the positions of astronomical objects in the sky at a given time; and the dust board (takht), a tablet covered with sand on which calculations could be made and erased. Most astrologers learned their practice by studying with a master, acquiring a basic knowledge of astronomy and mathematics and the ability to use astronomical instruments.
After taking the measurements and making their calculations, the astrologist would then interpret the signs and what they meant for the patron’s future. These interpretations were based on the large body of literature associated with astrology, from manuals for interpreting signs to treatises that ascribed certain personality traits to those born under each zodiac sign. These in turn influenced the artistic iconography of each sign, and so sample excerpts from the Kitab al-mawalid (Book of Nativities) by Abu Ma‘shar al-Balkhi, translated by Stefano Carboni, are included here with the objects bearing zodiacal imagery. Abu Ma‘shar (known as Albumasar in Europe), who also worked out a complex system of chronology, was considered a master of the discipline by later Arab scientists, and his works were later translated into Latin.
The Zodiac in Art
Because of the popularity of astrology in the medieval period, it became common to decorate objects with personifications of the planets and the Zodiac constellations. This reflected the belief that objects with astrological decoration had talismanic powers—that is, they were capable of influencing the occult power of the planets and stars, and thus protected the owner from sickness, bad luck, or defeat.
The symbols the Arab and Iranian astronomers used to represent each Zodiac constellation were derived from the images ancient Greek astronomers had used to describe them. These were a ram (known as the sign Aries, ); a bull (called Taurus, ); twins (called Gemini, ); a crab (called Cancer, ); a lion (called Leo, ); a female figure (called Virgo, ); scales (called Libra, ); a scorpion (called Scorpio, ); an archer (called Sagittarius, ); a kid goat (called Capricorn, ); a water-pourer (called Aquarius, ); and two fish (called Pisces, ). Objects such as these were especially popular from the late twelfth to the fourteenth century in Egypt, Syria, and Iran. Several are inscribed with the names and titles of rulers, and it is believed that on objects so closely associated with a particular ruler, representations of the sun, planets, and stars also symbolized the power of that patron .
In representing the Zodiac constellations, artists of this period mostly copied Greek models. The personifications of the planets, on the other hand, had few iconographic precedents, and so imagery for each evolved from the characteristics each was attributed in the Islamic astrological writings, including a color, an occupation, and a day of the week. Thus Mercury was a scribe, depicted as a young man writing on a scroll of paper; Venus was a female musician, shown playing an instrument; Saturn was a dark-skinned old man holding a pickax; Jupiter was a sage or a judge, wearing a turban; Mars was a warrior, holding a sword and a severed head; and the sun and the moon were human figures holding a sun disk and a crescent, respectively . In addition to the seven traditional planets, it was believed that there was an eighth, invisible planet, named in Arabic al-tinnin (“the dragon”), or Jauzahr. Depicted as a figure flanked by snakes with dragon heads, Jauzahr appears on objects alone and with the signs of the Zodiac .