Astrolabe of Ibn Said al-Sahli

Brass planispheric astrolabe, consisting of a body or “mater” that contains five plates engraved on both sides (for ten latitudes), a rete or “star net” with pointers for twenty-four stars, an alidade and a frontal rule added at a later date. A zodiac calendar, a Julian calendar and an altitude scale or “shadow square” are engraved on the front. According to the inscription, it was made in 459 AH (AD 1067) by Ibrahim ibn Sa’id al-Sahli, who also crafted two other specimens currently in Oxford (History of Science Museum) and Rome (Museo Astronomico e Copernicano dell'Osservatorio Astronomico di Roma). This instrument, invented by the Greeks, was used to calculate the position of the sun and stars, measure altitude and distance, and even served as a calendar and clock.
It is the only medieval astrolabe in the collections of the National Archaeological Museum. The piece was part of the museum’s founding collection, transferred from the former Museum of Medals and Antiquities of the National Library after it was purchased from Faustino de Borbón in 1798.