Brass astrolabe with silver inlay

This astrolabe has seven latitude plates. The rete is marked with pointers to sixty-three important stars and the mater is inscribed with a gazeteer of 103 cities throughout the Islamic world, including Jerusalem, Damascus, Baghdad, Kabul and Delhi. Using the data provided in the gazeteer, an educated person could calculate from each location the direction of Mecca, which Muslims must face during daily prayer.

A calligraphic inscription at the top of the astrolabe praises the royal patron, Sultan Husayn, at length. It is written in a dense, elaborate style, and many of the metaphors are appropriate to the astronomical instrument, describing the Shah as:

'…the centre of the sphere of power and justice, the pole of the supreme heaven of magnificence and grandeur, the flashing star of the apogee of the world conquest, the resplendent sun of the midst of the heavens of world government.'

Two craftsmen have signed the back of the instrument, the astrolabe-maker cAbd al-cAli ibn Muhammad Rafi' al-Juzi'i, and his brother Muhammad Bakir, who carried out the inscriptions.

The massive size and weight of this instrument show that it was more for conspicuous ostentation than use. To measure the altitude of a star, for example, an astrolabe must be lifted up (held by the ring at the top) and held above eye-level – which would be quite impossible with this particular object! Not long after its production, possibly after Sultan Husayn died, in 1722, the astrolabe was acquired for the British collector Sir Hans Sloane. Shortly afterwards, the instrument changed hands again, when Sloane's collection was acquired by the British Museum after his death, in 1753.