Excerpts from Books and Wikipedia
"The Abbasid caliph al-Mamun (r.813-33) founded the House of Wisdom at Baghdad for the translation of Greek, Persian, and Hindu works into Arabic. . . . Arab astronomers built on the achievements of the ancient world, improving the accuracy of star catalogues and refining the design of astronomical instruments, including the astrolabe. . . . When medieval Europeans rediscovered this knowledge in the twelfth century, it was usually from Arabic translations of the original Greek works." [Furtado: 1001 Days] "Refined by the Arabs from these early Greek designs, the astrolabe was a virtual bronze book of the stars that projected the spherical universe onto a two-dimensional face. . . . It drew on classical sources but then went well beyond them to refine the device and to address the burning questions of the day in such fields as timekeeping, astronomy, astrology, and cartography." [Lyons: House of Wisdom, p. 38-9] The astrolabe, an ancient tool of navigation, was first used in Europe in 1050. [Timeline of Middle Ages]