Astrolabe

The astrolabe, an instrument that measures the positions and altitudes of planets, stars, and the sun, originated in ancient Greece and was perfected by medieval Arab astronomers. In the Islamic world, which greatly valued both astronomy and astrology, astrolabes had added religious significance for their ability to calculate the direction of Mecca for daily prayers. The front of an astrolabe includes a removable, recessed plate with stereographic projections of the northern celestial hemisphere. Layered on top is a rotating disk known as a spider adorned with pointers to indicate key stars on the plate below. The example on view, however, is a nonfunctional forgery in the style of a renowned Persian astrolabist. Instead of accurate pointers, this astrolabe uses stylized flourishes that do not line up realistically with the stars below.