Measuring time by the stars: Astrolabe

Essential information

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Royal Observatory, Meridian Line and Historic Royal Observatory, Time & Society gallery

It's beautiful, sure, but can you imagine what it is used for?

An astrolabe is an impressive instrument which was used by astronomers for centuries to measure and predict the positions of the Sun and stars to calculate the observer’s time, location and date. Some versions were also used by Islamic astronomers who would use one to accurately calculate the time for prayers and other events for the faithful.

If the dating on this astrolabe is correct, then it belongs to the later period of Muhammad Khalil's activities. The decoration, by Muhammad Baqir Isfahani, has been very skillfully executed. The throne is extensively ornamented with floral motifs on both sides. The suspension ring is chiselled with a neat series of geometric patterns, which is repeated in a slightly different way on the shackle.

Engraved along the rim of the mater is an invocation to the Prophet, his mother Fatima and the 12 Imams of Twelver Shi'ism.

There are six standard plates for a range of latitudes from 22º-39º.

Inside the shadow square is a large cartouche with the maker's signature: 'Made by the humble and wretched in front of God the Magnificant, 'Muhammad Khalil ibn Hasan 'Ali''. Beneath this is the signature of the decorator: 'Muhammad Baqir Isfahani'.

The number 19 precedes this signature which is presumed to be the date: AH[11]19, which is 1707-08 AD.