In its origins and development, Islamic astronomy closely parallels the genesis of other Islamic sciences in its assimilation of foreign material and the subsequent amalgamation of the disparate elements of that material to create a science that was essentially Islamic. Before we consider the literary and observational activities of Islamic astronomers, which lasted for over a millenium, we should glance briefly at the traditional astronomy of the Arabian peninsula.

FOLK ASTRONOMY

Traditional Arabic astronomy was closely linked to the anwā' (sing. naw'), a word that denotes in the singular the acronycal (i.e. occurring at nightfall) setting of a star or constellation and the heliacal rising of its opposite. Anwā' denotes the whole system based upon the settings and rising of stars and constellations, and it also appears in the titles of a number of works that constitute a separate class of their own.

To estimate the passage of time the early Arabs possessed a primitive system. This consisted basically of two distinct elements. First, the acronycal setting of a series of stars or constellations marked the beginning of periods called naw', but within which the duration of the naw' proper was from one to seven days; the stars themselves were responsible for rain and were invoked during rain-making ceremonies. Knowledge of these anwā' enabled Beduin trained in the science to foresee the state of the weather during a given period. Secondly, the heliacal rising of the same series of stars or constellations, at six-monthly intervals, marked out the solar year by fixing the number of periods, probably about twenty-eight. Fragments of folklore that have survived suggest that this was the basis of the calendar.

Some time before Islam the Arabs learned from the Indians to distinguish the stations or 'mansions' ( manzila, pl manāzil) of the moon, numbering twenty-eight.