c. 964

Andromeda Sighted

‘Abd al-Rahmān al-Sūfī (903–986)

Another important early astronomer from the Arab world was ‘Abd al-Rahmān al-Sūfī of Persia (modern-day Iran). Like most other astronomers of the Middle Ages, al-Sūfī was aware of the major aspects of classical Greek astronomy and cosmology, including Ptolemy’s Almagest, which he translated into Arabic. He and others sought to expand on Ptolemy’s ideas, and to synthesize them with new observations and theories from early Arabic astronomy. His results were published around the year 964 in a landmark work called The Book of Fixed Stars.

Al-Sūfī’s book was essentially a detailed map of the stars in the 48 then-known classical Greek constellations, using star data based on Ptolemy’s older catalog in the Almagest and Hipparchus’s Stellar Magnitude system, but refined or corrected using his and other newer observations of stellar brightnesses and colors. The Book of Fixed Stars uses the Arabic names for the bright stars in each constellation; we still use many of these star names—including Altair, Betelegeuse, Deneb, Rigel, and Vega—today.

The inset above shows a drawing of part of the constellations Andromeda and Pisces from al-Sūfī’s 964 Book of Fixed Stars.

In the section of al-Sūfī’s book devoted to the constellations Andromeda and Pisces, he notes a “little cloud” detected among the major stars. Although he could never have known it, al-Sūfī is widely believed to have made the first recorded observation of the Andromeda galaxy, the nearest (about 2 million light-years distant) spiral galaxy to the Milky Way. Also known as Messier object 31, Andromeda is nearly eight times larger than the full Moon, but it is extremely faint and thus takes excellent eyesight and patience to detect. Al-Sūfī was also the first to detect other faint star clusters, nebulae, and “clouds,” including one of the Milky Way’s faint elliptical companion galaxies in the southern skies, an object that, 550 years later, was named the Large Magellanic Cloud because it was prominently noted and popularized in Europe after Ferdinand Magellan’s voyage around the world in 1519.

A modern digital astronomical photograph of the Andromeda galaxy, viewed in ultraviolet light from the NASA Galaxy Evolution Explorer satellite.