9th Century Brass Astrolabe

This particular astrolabe dates from the time of the first Holy Roman Emperor, Charlemagne, around 832 A.D. It uses two plates for latitudes corresponding to the regions between Persia and the Black Sea. Astrolabes are portable astronomical calculators used to tell the rising and setting times of the sun and a number of fixed stars in a number of locations. It can also be used to determine height and distance by the geometric method of triangulation.