Jim Al-Khalili: Inspirations

  • 11 September 2012
  • By Jim Al-Khalili
  • Professor of Theoretical Physics, University of Surrey

The physicist, author and broadcaster explains his captivation with a 'Cinderella astrolabe'.

A couple of years ago I had the opportunity to visit the stunningly beautiful and serene Museum of Islamic Art in Doha, Qatar. After wandering through many rooms displaying vividly coloured tiles, pottery, sculptures and examples of early Kufic calligraphy, I eventually found myself in a small room surrounded by dozens of beautiful astronomical instruments called astrolabes.

They were displayed alongside each other in row upon row, all seemingly clamouring for my attention like Miss World contestants, each one more intricate and shiny than the last. Here were a thousand years of craftsmanship and science from across the Islamic world: astrolabes from Andalusia to India and everywhere in between.

I stood alone in this cool, softly lit room, trying to decide what criteria I should apply to help me choose the winner of the Miss Astrolabe beauty contest, when I realised I had not really taken in some of the other, less glitzy displays; and that was when I caught sight of it in an alcove on the far wall.

Astrolabe, 9th or 10th century Museum of Islamic Art, Doha

Astrolabe, 9th or 10th century

It really was a sad excuse for an astrolabe, seemingly shunned by its more illustrious and elaborate neighbours. The caption described it blandly as a mathematical and astronomical instrument dating back to late 9th- or early 10th-century Baghdad.

It appeared rather basic in function, consisting of a battered and bruised brass disk, about 15 centimetres in diameter, with engraved notches around its perimeter signifying angles and a revolving alidade (pointer) overlying it. Saddest of all was a small hole punched in it, looking very much like it had been made by a bullet. I know that seems rather unlikely, but it nevertheless gave the impression of having been mortally wounded in battle.

What fascinated me most though was the significance I believe it holds in representing one of the most momentous periods in the history of science, for this instrument would very likely have been used by early Islamic astronomers repeating some of the measurements of the Ancient Greeks that they had found tabulated in the writings of Ptolemy.

Since I cannot be certain how accurate the dating of my astrolabe is, I feel I should be allowed the somewhat fanciful notion that it was the property of one of a group of remarkable men brought together during the first half of the 9th century by that greatest of all the Islamic patrons of science and scholarship, the Abbasid caliph al-Ma’mūn, son of the more famous Harun al-Rashid.

A consequence of bringing together for the first time a wide range of different scientific traditions from around the world was that the astronomers of Baghdad had at their disposal a far broader world-view than anyone before them. Differences in the translations of Persian, Indian and Greek astronomical texts, each with its own cosmological model, set of measurements and tables of astronomical values, not always in agreement with each other, meant they could not all be right.

For al-Ma’mūn’s astronomers, to be able to compare and comment objectively on the many translated texts with fresh eyes and open minds must have been gloriously exciting. Questions started to be asked and doubts raised. Clearly, discrepancies needed to be resolved, and it became apparent that there was an urgent need for a new set of comprehensive astronomical measurements to be made.

Sometime during the second decade of the 9th century, al-Ma’mūn ordered the building of the first astronomical observatory in Baghdad. Could my instrument have possibly belonged to one of the remarkable men who worked there? Any one of them might have pondered the heavens by using its sighting arm to measure and record the positions of the celestial bodies in the night sky.

This group of medieval astronomers was just the first in a long line of great Arab and Persian scholars who laid the groundwork for the birth of modern astronomy at the hands of later and more illustrious European giants such as Copernicus, Kepler and Galileo. Many observations of the sun and moon were carried out in Baghdad and a table with longitudes and latitudes of dozens of stars was drawn up.

On completion of all the measurements, a new zij, or star chart, was produced for the caliph. So influential was their work that even Christopher Columbus is known to have used their calculation of the circumference of the earth to convince his backers to fund his famous voyage.

I wonder what role my sad little instrument played in all this, back when it would have been polished and proud, playing its small part in mankind’s quest to understand the cosmos.