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.

It is customary to begin an account of the planispheric astrolabe by explaining the projection of the celestial sphere on to the equatorial plane; the spherical astrolabe provides the material counterpart to the sphere in this geometrical relationship and so is much used in modern astrolabic pedagogy. However, despite being lauded in contemporary Islamic written accounts, the instrument must have been difficult to make, inconvenient to use, and relatively fragile - the Oxford spherical astrolabe is unique, at least in terms of its survival.