Database: Astronomy and Astrology
It is said that if you are ever lost in a desert, looking at the stars will help you steer your way to safety. Like their Umayyad predecessors, the Abbasid caliphs certainly believed in the usefulness of stargazing and funded the construction of observatories and the translation of many Greek, Indian, and Persian astronomical works. One of the most important Arabic works of astronomy from this period was the 10th century Treatise on the Fixed Stars (a commentary on Ptolemy's Almagest) of Abd al-Rahman al-Sufi (903-986). Illustrated with depictions of stars and constellations known from classical antiquity, it was widely copied and used for centuries after. Al-Sufi is credited as the first astronomer on record to have observed the Andromeda Galaxy!
Abbasid astronomers were not only interested in the science of astronomy, they were also interested in its practical applications, especially astrology, the art of determining auspicious days for activities. For instance, al-Mansur sought the help of astrologers in choosing where and when to build Baghdad.
Attempting to decipher the future in such a way required an extensive understanding of the movements of the heavenly bodies. Time-consuming observations and elaborate calculations were needed to create astronomical tables that described the precise positions of the moon, the sun and the five known planets—Mercury, Venus, Mars, Saturn, and Jupiter. Special events such as floods and invasions were noted next to them and could be used to suggest causality between the stars and human life. Astronomy was therefore seen as a tool for astrology, but it could also be used on its own for calculating prayer times or land surveying. Whatever their final objective, Abbasid-era astronomers contributed enormously to astronomical knowledge, and were responsible for the discovery of many stars (Altair, Aldebaran) and the coinage of many astronomical terms (azimuth, nadir) that are still used today.