English Planispheric Astrolabe

The astrolabe is an astronomical calculating device used from ancient times into the eighteenth century. The openwork piece on the front, called the rete, is a star map of the northern sky. Pointers on the rete correspond to stars – on this “zoomorphic” instrument they are in the shape of animal tongues. The outermost circle is the Tropic of Capricorn, and the circle that is off-center represents the zodiac, that is to say the apparent annual motion of the sun. On the brass instrument, the scales below the rete are for a latitude of 52 degrees (there are no separate plates). Measuring the height of a star using the sighting device on the front, one could set the map to find the time of night and the position of other stars.

The brass instrument was made in England, perhaps before 1500, although the sundial scale drawn on the back is of a later date.

Reference:

For a detailed description of this object, see Sharon Gibbs with George Saliba, Planispheric Astrolabes from the National Museum of American History, Washington, D.C.: Smithsonian Institution Press, 1984, pp.15, 23, 45-47, 153-154. The object is referred to in the catalog as CCA No. 2006.

John Davis, "Two Medieval English Astrolabes in the Smithsonian Museum," Bulletin of the Scientific Instrument Society, 2023, #157, pp. 2-17. Davis dates this instrument to the second half of the fourteenth century.

Currently not on view