Al-Ṣūfī made his astronomical observations at a latitude of 32.7° N in Isfahan. It has been claimed that he identified the
Large Magellanic Cloud, but this appears to be a misunderstanding of a reference to some stars south of Canopus, which he admits he did not observe. He also made the earliest recorded observation of the
Andromeda Galaxy in 964, describing it as a "small cloud". This was the first
galaxy other than the
Milky Way to be mentioned in writing.
Astrolabe Al-Ṣūfī also wrote about the
astrolabe, identifying numerous additional uses for it. According to American Near Eastern scholar Adam L. Bean, al-Ṣūfī's work describes over 1,000 different uses in areas as diverse as
astronomy,
astrology and horoscopes,
navigation,
surveying,
timekeeping, determining the
Qibla, and performing
Salat prayer.
'' ("The Book of Fixed Stars''") Mardin, 1131 CE. Al-Ṣūfī published ''
("The Book of Fixed Stars''") in 964, and dedicated it to Adud al-Dawla, the ruler of
Buwayhid at the time. This book describes 48 constellations and the stars within them. Al-Ṣūfī compared Greek constellations and stars as described in
Ptolemy’s
Almagest with Arabic ones, linking those that were the same. He included two illustrations of each constellation, one showing the orientation of the stars from the perspective outside the
celestial globe, and the other from the perspective of looking at the sky while standing on the Earth. He separated them into three groups; 21 seen from the north, 15 seen from the south, and the 12
zodiac constellations. He included a complete set of
star charts, that included the names and numbers of the individual stars in each of the 48 constellations, and each star's
longitudinal and latitudinal coordinates,
magnitude, and location north or south of the
ecliptic.
Scribal errors within the 35 surviving copies of
The Book of Fixed Stars have caused the value of the magnitude for a particular star to vary from manuscript to manuscript. Al-Ṣūfī organized the stars in each of his drawings into two groups: those that form the image depicted, and others that are in close proximity to the image. He identified and described stars not included by Ptolemy, but he did not include them in his own star charts. Stating that his charts were modelled after Ptolemy, he left the stars excluded in Ptolemy's catalogue out of his charts as well. To allow for the longitudinal placement of the stars within constellations having changed over the eight centuries since the
Almagest was written, Al-Ṣūfī added 12° 42' to all the longitudes values provided by Ptolemy. Al-Ṣūfī differed from Ptolemy by having a three level scale to measure the magnitude of stars instead of a two level scale. This extra level increased the precision of his measurements. His methodology for determining these magnitude measurements cannot be found in any of his extant texts. Despite the importance of
The Book of Fixed Stars in the
history of astronomy, it took more than 1000 years until the first partial English translation of the book was published in 2010. ==Legacy==