Astrolabe

An astrolabe is a historical astronomical instrument, most closely associated with medieval Islamic and later European astronomy, that models the visible positions of the sun, stars and horizon on a rotating flat disk, allowing its user to calculate the time of day or night, determine latitude, and solve a range of practical astronomical and astrological problems. Building on earlier Greek instruments and mathematical principles developed by figures such as Hipparchus and Ptolemy, the astrolabe was substantially refined by astronomers in the medieval Islamic world from around the eighth and ninth centuries, who greatly expanded its practical applications, including determining the times of Islamic prayer and the direction of Mecca. Transmitted to medieval Europe partly through Islamic Spain, the astrolabe became one of the most widely used scientific instruments of the medieval and early modern periods, valued for navigation, timekeeping, surveying and astronomical calculation, before being gradually superseded from the seventeenth century onward by more specialized instruments such as the sextant and mechanical clock.