A Note upon al-Bāsī’s Astronomical Tables

‘Uṯmān al-Bāsī was an astronomer from Djerba (Tunisia) who lived in the second half of the eighteenth century. He compiled a set of tables for constructing a solar quadrant (rūḫāma). We describe the mathematical structure of the methods for determining the solar azimuth, the equation of half daylight and the solar azimuth corresponding to the hour-angle. We apply these methods to explain three tables which have not been properly understood in modern times. We attempt to determine the various stages of al- Bāsī’s research which enabled him to construct and set up these tables.