A Companion to the Philosophy of Technology

Practical Astronomy, Surveying and Time-keeping

Medieval Muslims developed an approach to astronomy that was based on Greek astronomical theory (especially Ptolemy’s Almagest), Indian astronomical tables, and the astrolabe, an observational tool that performed a variety of tasks including finding the time of the day or year or of a celestial event, or determining latitude. Finding the qibla (the direction of Mecca) astronomically gave rise to a specific body of tables. An astrolabe, or a simplified version of one, could be used in navigation to determine the altitudes of the sun, the moon, the pole star or other celestial bodies. Arab ship captains, however, preferred a simpler instrument, a wooden block and knotted string called the kamal, which was used to take celestial altitudes.

In the medieval Islamic world there was a well-defined science of astronomical time-keeping called ‘ilm al-miqat. It was used, first, to determine the five daily canonical hours of prayer. A muezzin could do this with an astrolabe, or a professional astronomer called a muwaqqit could be hired. At the popular level, the hours of night could be determined by anybody who knew some astrology by looking at the lunar mansions; in daytime, by measuring the length of one’s own shadow – and there were twenty or more methods of how to do this. At the learned level, scholars like al-Khwarizmi wrote prayer-tables for each latitude. Muezzins were enjoined to use astronomical tables for determining prayer times ...