overall: 24.3 cm x 17.9 cm x 3.6 cm; 9 9/16 in x 7 1/16 in x 1 13/32 in
The astrolabe is an astronomical calculating device used from ancient times into the nineteenth century. Measuring the height of a star using the alidade on the back of the instrument, and knowing the latitude, one could find the time of night and the position of other stars. The openwork piece on the front, called the rete, is a star map of the northern sky. Pointers on the rete correspond to stars; the outermost circle is the Tropic of Capricorn, and the circle that is off-center represents the zodiac, the apparent annual motion of the sun. Engraved plates that fit below the rete have scales of altitude and azimuth (arc of the horizon) for specific latitudes. This brass astrolabe has a rim with throne attached to a back plate with throne, handle, ring, three plates, an alidade with pin, a rete, and a wedge at the front that holds the instrument together. The instrument is signed: ‘Ali ben Mu[. . .]ammad ben Abdallahben Faraji. The inscriptions are in the script of the western Arabic world.
For a detailed description of this object, see Sharon Gibbs with George Saliba, <a href="https://repository.si.edu/handle/10088/2444"><I>Planispheric Astrolabes from the National Museum of American History</I></a>, Washington, D.C.: Smithsonian Institution Press, 1984, pp. 17, 171-173. The object is referred to in the catalog as CCA No. 2571.
Currently not on view
Gift of International Business Machines Corporation