Astrolabe with Universal Lamina, by `Ali ibn Ibrahim al-Harrar, Taza, Morocco, 1327/8

Parts

It comprises: a mater, a rete, an alidade, a screw pin.

Throne

The throne is of the simple type and it is attached with an integrated base. The throne is pierced by two small holes on each side of the shackle. The front is integrated with the limb; the back with the back plate.

Ring

The ring is of the simple, squared cross-section type (i.e. a simple ring made from a round rod or piece of metal).

Shackle

Shackle of the omega type (i.e. Ω-shaped shackle).

Mater

The mater and limb are of two pieces, riveted construction. The rim is marked with a degree scale 0-360° divided every 5 degrees, subdivided every degree, and labelled in Abjad numerals every 5 degrees.

Womb

The womb contains a universal projection with an set of almucantars for 90°.

Back

On the back shown above, are a zodiac/calendar scale (0° Aries = 13.5 March; concentric type); an unequal-hour diagram; a sine and cosine graph; a shadow-square; and the usual scales of degrees.

Rete

The rete is of the leaf type and it a "Universal Lamina". The rete of this instrument is made for 58 stars.

The 'Universal Lamina' is a combination of a rete similar to that of a conventional astrolabe, super-imposed on a universal projection of the type used by az-Zarqellu. The rete is usually divided into two halves along the Eest-West line, the tracery in the upper half representing almucantars and azimuths, that in the lower half being part of the usual stereographic projection, on the plane of the Equator, of the ecliptic and certain fixed stars. The outer circle of the rete represents the Equator and not, as on a conventional rete the Tropic of Capricorn. The almucantars and azimuths usually found in the upper half, have been replaced by the second half of the ecliptic circle and a further selection of fixed stars. The so-called Zarqellu projection below the rete is of the usual type, to which have been added azimuth circles, as on a normal astrolabe plate for latitude 90°. The result is that for certain operations it is convenient to use the rete at the same time considering the Zarqellu projection as an ordinary plate for latitudes 0° and 90°; and for other operations to use the universal projection and to ignore the rete.

Zodiac label

The zodiac on the rete is labelled: الحمل , الثور , الجوزا , السرطان , الاسد , السنبله , الميزان , العقرب , القوس , الجدي , الدلو , الحوت.

Pin and horse

The rete is attached using a rivet. Although the head of the rivet is slotted as if it were a screw, it rotates freely an does not unscrew. There is no apparent way to remove this rivet and thus inspect the back of the rete or rule.

Alidade

Double-ended. The rule has an usual triangular cross-section.