An astrolabe is a portable, hand-held, circular object that represented the spherical universe on a flat, plane surface. It allowed astronomers to read the skies for timekeeping, to chart the movement of the Sun, Moon, planets and stars and cast astrological horoscopes. In Islamic society, the astrolabe was especially useful for determining the five daily prayers, the direction of Mecca (qiblah) and the months of the lunar year. But an astrolabe could be used to calculate more complex astronomical data too: it is, after all, ‘an astronomical computer’.
