Astrolabe Catalogue

astrolabe, inventory number 41122 from North Africa, 13th century
thumbnail for astrolabe (front), inventory number 41122 from North Africa, 13th century
thumbnail for astrolabe (back), inventory number 41122 from North Africa, 13th century
thumbnail for astrolabe (rete front), inventory number 41122 from North Africa, 13th century
Date13th century
PlaceNorth Africa
Inventory no.41122
AcquisitionBequeathed by T. G. Barnett in 1935

The back of this instrument bears a universal projection based on that developed by Ibn az-Zarqāllu. One of the characteristics of the common astrolabe was that the projection of the heavenly sphere varied with the latitude. For this reason, typical planispheric astrolabes contain a number of tympans, each engraved for a specific latitude. Instrument makers saw in this an intellectual challenge: to develop a universal projection that would serve all latitudes and thus obviate the need for the various plates. Az-Zarqāllu's universal projection was not the earliest solution to this problem; it does, however, represent a further simplification of the projection and by including a selection of fixed stars removes the need for a rete.

Az-Zarqāllu's advance was to include two sets of coordinates on a single projection. First, there is a set of equatorial coordinates, those across the horizontal line (the equator) in the picture. To these are added a set of ecliptic coordinates, found along the ecliptic and its axis (on this instrument, the ecliptic is inclined downward to the right and bears the names of the zodiacal signs). Prominent fixed stars are then placed according to their celestial longitude and latitude.

On this particular astrolabe, only an abbreviated set of ecliptic coordinates have been included. Five arcs indicate divisions of the zodiac, but no effort has been made to indicate the declination scale. There is a complete set of equatorial coordinates. The maker also included 29 stars, of which 28 are named. With a complete regula, which would have included a vertical ruler, this plate would have been perfectly useable for most of the functions performed by a normal astrolabe.

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Throne, Ring and Shackle

The throne is of the five-lobed type made of brass attached with integrated base made of brass and has a simple, squared cross-section ring made of brass and omega type shackle made of brass . More information


The mater and limb are of two pieces, riveted construction. There is a notch at the throne that accepts the tabs from the tympans and keeps them from rotating. Scales on the limb: degree scale.

The limb is inscribed: with a miscellaneous marked as [Along edge of limb]. The edge of the limb is divided into 91 approximately equal divisions, each marked with some characters. The use of this scale or these inscriptions is not immediately obvious. More information


The back of this astrolabe bears an az-Zarqellu projection. The back contains 0 scales. The universal on the back contains 2 scales. More information

Rete, Pin & Horse

The rete contains 29 stars. The zodiac on the rete is labelled: حمل , ثور , جوزا , سرطان , اسد , سنبله , ميزان , عقرب , قوس , جدي , دلو , حوت .
The rete is attached using a pin & horse. Probably a replacement. More information


There are 4 plates with latitudes ranging from 31°0' to 47°0' . More information

Rules & Alidades

Type Details
AlidadeDouble-ended. The rule is not original.
More information


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