By the ninth century, Islam had expanded into regions where a knowledge of the stars and their movements had long helped in the calculation of time, the prediction of weather and river floodings, and navigation across trackless deserts. During the eighth and ninth centuries, under the rule of the first Islamic dynasties (the Umayyads and Abbasids), scientists built upon this knowledge to develop new theories and instruments. Court patronage also supported an intensive program of translation of Greek, Sanskrit, and Pahlavi (early Persian) astronomical texts into Arabic, a practice that was instrumental in preserving this important body of knowledge.
One of the most influential of these translated works was Ptolemy's Almagest (the Latinized version of the Arabic title al-Majisti, or "Great Compilation"). The treatise, which describes the circular motion of the sun and the planets around a fixed earth, became the most important point of departure for astronomers working in the Islamic world. Supported by their own observational records, they identified discrepancies between scientific models and reality and set out to create theories regarding the celestial bodies that would address these inconsistencies.
Significantly, astronomical knowledge fulfilled a utilitarian function in the Muslim world by facilitating the proper ritual practice of Islam. Daily prayers occur at times determined by the sun's position and are always performed facing the direction of the holy city of Mecca, where the Ka'ba, Islam's holiest shrine, is situated. The Islamic calendar is a lunar one, which means that every month starts when the new moon first becomes visible. Precise observation of the moon is crucial to determine holidays and other key dates, such as the start of the month of Ramadan, when Muslims are required to fast during daylight hours.
Though not considered a science today, astrology used to be regarded as a branch of astronomy. In practice, astrology is largely concerned with understanding the influence of the stars on earthly events. Astrologers therefore needed an in-depth understanding of the movement of the planets and the locations of the stars. Serious scientists such as Abu Ma'shar al-Balkhi (787–886), al-Biruni (973–1048), and Nasir al-Din al-Tusi (1201–1274) all wrote astrological treatises.
Observational astronomy flourished in the Islamic world, where sophisticated observatories and instruments were developed. Observatories were centers of learning and research that also housed libraries containing thousands of books. The Caliph al-Ma'mun (reigned 813–33) built the first observatory in Baghdad in the ninth century. His patronage enabled astronomers to prepare tables describing the motions of the sun and moon, star catalogues, and descriptions of the instruments used.
The accuracy of medieval Islamic observatories and astronomical instruments was remarkable. In fact, the calculations of famous observatories in Samarqand (in present-day Uzbekistan) and Maragha (in present-day Iran) differ from contemporary calculations by only a fraction of a percent. In addition to the large stationary instruments at observatories, scientists working under Islamic patronage were also successful in developing smaller portable tools such as the astrolabe (used for mapping and astronomical calculations), the astrolabic quadrant, and the celestial globe. The astrolabic quadrant, shaped like a ninety-degree pie segment, was used to record the location of stars and planets in the celestial sphere, the domelike shape the skies take when observed from the earth. The celestial globe (see the Austrian example from 1579 in the Museum's collection) was used for teaching and illustrative purposes, and for many was also a desirable decorative object. Over time, these portable tools made their way into Renaissance Europe, aiding in the development of similar astronomic instruments by European scientists. This is clearly seen in the astrolabes produced by sixteenth-century Italian and Flemish scholars, which are decorated with motifs and inscriptions similar to those on Islamic instruments. Moreover, Italian and Flemish scientists and architects produced detailed drawings of Near Eastern astrolabes, including refined reproductions of the engraved Arabic inscriptions. These drawings and astrolabes demonstrate knowledge of Arabic and an avid interest in Islamic instruments in sixteenth-century Europe.