Al-Sufi's ‘Book of the Fixed Stars’

Al-Sufi, born in Rayy in 903, seems to have spent his life close to the Buyid rulers: by his own statement he was at Dinavar in 946–947 and at Isfahan in 948–949 with Ibn al-Amid, the vizier of Rukn al-Dawla, and he dedicated his book to Rukn al-Dawla's son Adud al-Dawla, the ruler of Fars. The book is usually said to have been written at Adud al-Dawla's court in Shiraz, though some accounts place al-Sufi's work at Isfahan. Taking the star catalogue of Ptolemy's Almagest as his basis, he described each of the 48 classical constellations twice over — as the Greek astronomers had defined it and as the Arabs of the desert saw the same stars, with their own names and figures — drawing on earlier books on Arabic star lore that are now lost. For each constellation he drew two figures, one as it appears on a celestial globe and one as it is seen in the sky, and added a table of its stars with their coordinates and magnitudes.

The coordinates were not newly measured: al-Sufi adjusted Ptolemy's longitudes for the precession of the equinoxes, adding 12°42' for his epoch of 1 October 964. But he checked the brightness of the stars against the sky, correcting the magnitudes of about half of them on a finer scale than Ptolemy's, criticised the errors of his predecessors and noted objects absent from the Almagest — among them the ‘little cloud’ before the mouth of the Big Fish, an Arabic constellation, which is the Andromeda Galaxy: the first galaxy other than the Milky Way to be recorded in writing. The often repeated claim that he also described the Large Magellanic Cloud is a modern misunderstanding; it could not be seen from Shiraz.

The book remained a classic for centuries. Al-Biruni and Ulugh Beg quoted it, Nasir al-Din al-Tusi translated it into Persian, Alfonso X of Castile had a Castilian version made in the 13th century, and from Thomas Hyde's quotations (1665) Giuseppe Piazzi took many of its Arabic star names into his catalogue of 1814, through which they entered modern astronomy. Al-Sufi, known in Latin as Azophi, died in 986.