Flamsteed Astronomy Society

“Medieval Arabic Astronomy — Filling the gap between Ptolemy and Copernicus”

a talk by Prof Jim Al-Khalili — April 4, 2011

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Report by Chris Gadsden

Jim Al-Khalili is Professor of Theoretical Physics at the University of Surrey and also holds the Chair in the Public Engagement in Science.  He is well known as the presenter of several excellent TV science programmes.

Jim began by explaining that he was born in Baghdad and his father had the foresight to leave Iraq and settle in UK before Saddam Hussein was firmly in control.  He received all his secondary and further education in the UK.  Tonight’s lecture was based on his book “ Pathfinders — The Golden Age of Arabic Science” (Allen Lane 2010) which describes the contributions made by Arabic scientists based in Iraq, Persia, and other centres in the medieval Islamic empire.

In the 8th Century, Baghdad (the “Round City”) was the centre of the civilised world.  It was likely the largest city in the world from its foundation until the mid 10th century, with more than a million inhabitants at its peak.  Caliph Harun al-Rashid kick-started its development as the centre of learning and later, Caliph al-Mamun founded a new academy, “The House of Wisdom”.  Translations of ancient texts from Greek, Persian, Syriac, and Indian to Arabic were a key part of the early work and began the period known as “The Golden Age of Arabic Science”.  The Arabic scientists did much more than preserve ancient learning through the translation movement; they added very significantly to our body of knowledge.

Jim talked about Al Khwarizmi (c780-850), the father of algebra.  Indeed, the term algebra is derived from the arabic word al-Jebr ‘an equation’, and Al-Khwarizmi’s name, in it’s Latinized form Algorithmus, gives us the term algorithm. Al-Khwarizmi devised a method of measuring the circumference of the Earth and he played a major part in introducing the Arabs to Hindu numerals.  Evidence from some original manuscripts shows that the Islamic mathematicians were using decimal notation by the mid 9th century.

The next notable scholar of this period mentioned by Jim was al-Biruni (973 – 1048).  He was a Persian polymath and can be compared to Leonardo da Vinci.  One of his outstanding achievements was to measure the circumference of the Earth to an accuracy of 1%.  He did this by measuring the height of a mountain (in modern Pakistan), and by ingenious geometrical methods then deduced the radius of the Earth, and hence its circumference.


Prof Jim Al Khalili [Pics: Mike Dryland]

[Pics: Mike Dryland]