One of the Museum's most famous instruments, the spherical astrolabe is the only complete example of its type in the world. It dates from A.D. 1480/1, is signed as the work of Mûsà, and on stylistic grounds is thought to come from Eastern Islam. The inner, solid sphere has lines for altitude and azimuth together with lines for unequal hours, and thus performs the same function as the latitude plates of the more common planispheric astrolabe, namely the provision of a grid of local reference coordinates. On its surface moves the rete, which rotates to model the apparent daily motion of the heavens. The axis on which the rete rotates can be adjusted relative to the inner sphere in order to cater for the disparity between the appearance of the heavens in different latitudes. |