Flamsteed AS Dr Emilie Savage-Smith Islamic Astronomy

Flamsteed Astronomy Society

Mapping the Skies in Medieval Islam

Prof. Emilie Savage-Smith — Feb 5, 2007

Dr Emilie Savage-Smith talked to us about astronomy in the medieval Islamic period. She is Professor of the History of Islamic Science and Senior Research Fellow at St. Cross College, Oxford.

Most of us thinking about Islamic astronomy would only recall how the Islamic world preserved the texts from ancient Greece during Europe’s Dark Ages, and how over 200 of the star names we use today have been handed down from the Islamic astronomers, some from the Bedouin. In fact Islamic astronomy added greatly to the body of knowledge bequeathed by the Greeks. Islamic science views ancient Greece as much part of its heritage as we do in the west.

Star Catalogues — Abd al Rahman Al Sufi (d. 986CE *) compiled a catalogue (his Book of Fixed Stars) of 1022 stars with better accuracy than Ptolemy. Al Sufi’s ecliptic coordinates were advanced by 12˚ 10΄ from Ptolemy’s to allow for the precession of the equinoxes during the time between them.

Instrumentation — The Islamic period saw significant development in the making of precision celestial globes. These were used as computing devices and depicted an external view (so-called ‘God’s viewpoint’) of the heavens as if looking down at the ‘sphere of the stars’ from outside. Modern depictions are now usually an internal view of the heavens as seen from the surface of the Earth. After 60 to 70 years the globes (and astrolabes) were out of date because of precession. A hollow metal globe made in Lahore in 1663CE has no seam. Modern techniques can’t reproduce this object.

Astrolabes were developed to a high degree by the Islamic astronomers. The earliest surviving astrolabe was made in Baghdad in 870CE by Khafif, apprentice of Ali Ibn ‘Isa, involved in a survey to measure the length of a celestial degree.

An astrolabe is a flattened globe. Islamic legend attributes it to Ptolemy who was said to have accidentally dropped a globe which was then trodden flat by his horse. Ptolemy had no knowledge of the astrolabe though. Most astrolabes are calibrated for just one latitude, however the ‘Universal Astrolabe’ was devised in the 12th or 13th Centuries.

Observatories — The Islamic world lavished substantial wealth on building observatories. Ulugh Beg built a major observatory in Samarqand in 1420CE, containing a 40-metre quadrant. Facilities like this weren’t seen again until Tycho’s Uraniborg in the 1570s. These observatories were vulnerable to the tide of politics. The sixteenth century Istanbul Observatory operated only from 1575 to 1580CE when it was destroyed by fire during political upheaval.

Cosmology — Islamic cosmologists refined their models of planetary motion producing more accurate tables than Ptolemy. Thousands of ephemerides (books of tables) called ‘Zij’, were published. Ibn Al Shatir’s (d. 1375CE) model was as accurate as Copernicus’s, producing the same results for the position of Saturn. A Greek translation of al Shatir’s work was in Rome when Copernicus was there and it’s possible he was influenced by it.

What was the value of astronomy to the Medieval Islamic world? In fact very much the same as in Renaissance Europe which followed later — the ‘practical’ uses included:

The Calendar. The Islamic months begin with sighting of the new Moon and prediction of this is very important

Timekeeping & direction for prayers. Astronomy & the astronomical instruments were used to find the time and the direction of Mecca (called the Qibla) to organise prayers. As in later Europe, astronomers were often clerics.

Finding position on the Earth,

Astrology — much valued in Islam as later in Europe, and of course...

Prestige — wealthy patrons were benefactors in Islam as well as in western Europe.

MRD

CE = “Common era” (same reckoning as ‘AD’)

Ibn Al Shatir’s model of the motion of Mercury

The Constellation of Centaurus from al Sufi