Abd al-Rahman al-Sufi

'Abd al-Rahman al-Sufi ( (December 7, 903 in Rey, Iran – May 25, 986 in Shiraz, Iran) was a Persian astronomer also known as 'Abd ar-Rahman as-Sufi, 'Abd al-Rahman Abu al-Husayn, 'Abdul Rahman Sufi, or 'Abdurrahman Sufi and, historically, in the West as Azophi and Azophi Arabus. The lunar crater Azophi and the minor planet 12621 Alsufi are named after him. Al-Sufi published his famous "Book of Fixed Stars" in 964, describing much of his work, both in textual descriptions and pictures. Al-Biruni reports that his work on the ecliptic was carried out in Shiraz. He lived at the Buyid court in Isfahan.
Biography.
'Abd al-Rahman al-Sufi was one of the nine famous Muslim astronomers. His name implies that he was from a Sufi Muslim background. He lived at the court of Emir Adud ad-Daula in Isfahan, Persia, and worked on translating and expanding Greek astronomical works, especially the "Almagest" of Ptolemy. He contributed several corrections to Ptolemy's star list and did his own brightness and magnitude estimates which frequently deviated from those in Ptolemy's work, with only 55% of Al-Sufi's magnitudes being identical to Ptolemy's.
He was a major contributor of translation into Arabic of the Hellenistic astronomy that had been centered in Alexandria, Egypt, the first to attempt to relate the Greek with the traditional Arabic star names and constellations, which were completely unrelated and overlapped in complicated ways.
Astronomy.
Al-Sufi made his astronomical observations at a latitude of 32.7° in Isfahan. He identified the Large Magellanic Cloud, which is visible from Yemen, though not from Isfahan; it was not seen by Europeans until Magellan's voyage in the 16th century. He also made the earliest recorded observation of the Andromeda Galaxy in 964 AD; describing it as a "small cloud". These were the first galaxies other than the Milky Way to be observed from Earth.
Al-Sufi published "Kitab al-Kawatib al-Thabit al-Musawwar" (also commonly known as the "Book of Fixed Stars") in AD 964 and dedicated it to Adud al-Dawla, the current ruler of Buwayhid at the time. This book describes forty-eight constellations and the stars that they are composed of. Within the "Book of Fixed Stars", Al-Sufi compared Greek and Arabic constellations and stars to equate the same ones to each other. He included two illustrations of each constellation, one showing the orientation of the stars from the perspective of outside the celestial globe and the other from the perspective of looking at the sky while standing on the earth. He separated the constellations into three groups: twenty-one northern constellations, twelve zodiac constellations, and fifteen southern constellations. For each of these forty-eight constellations, Al-Sufi provided a star chart that contains all of the stars that form the constellation. Each star chart names and numbers the individual stars in the constellation, provides their longitudinal and latitudinal coordinates, the magnitude or brightness of each star, and its location north or south of the ecliptic. Although the magnitude was given for each star, of the 35 remaining copies of the "Book of Fixed Stars" the star magnitudes are not consistently the same number for each star due to scribal error. Al-Sufi organized the stars in each of his drawings into two groups: the stars that form the image that the constellation is meant to depict, and the stars that are in close proximity to the constellation but do not contribute to the overall image. He identified and described stars that Ptolemy did not, but he did not include them in his star charts. Al-Sufi states at the beginning of the "Book of Fixed Stars" that his charts are modeled after those that were produced by Ptolemy, so Al-Sufi left them out of his charts as well.
Eight hundred thirty-nine years had passed since Ptolemy had published the "Almagest," so the longitudinal placement of the stars within constellations had changed. To account for the procession of the stars, Al-Sufi added 12° 42' to the longitudes Ptolemy had previously suggested for the placement of the stars. Al-Sufi differed in Ptolemy by having a three leveled scale to measure the magnitude of stars instead of a two leveled scale. This extra level increased the accuracy of his measurements. His methods of determining these magnitude measurements cannot be found in any remaining texts.
Despite the importance of the Book of Fixed Stars in the history of astronomy, there is no English translation of the work.
Al-Sufi observed that the ecliptic plane is inclined with respect to the celestial equator and more accurately calculated the length of the tropical year.
Al-Sufi also wrote about the astrolabe, finding numerous additional uses for it: he described over 1000 different uses, in areas as diverse as astronomy, astrology, horoscopes, navigation, surveying, timekeeping, Qibla, Salat prayer, etc.
Al-Sufi's astronomical work was used by many other astronomers that came soon after him, including Ulugh Beg who was both a prince and astronomer.
Tribute.
Since 2006, Astronomy Society of Iran – Amateur Committee (ASIAC) hold an international Sufi Observing Competition in the memory of Al-Sufi. The first competition was held in 2006 in the north of Semnan Province and the second was held in the summer of 2008 in Ladiz near the Zahedan. More than 100 attendees from Iran and Iraq participated in the event.
On December 7, 2016, Google Doodle commemorated his 1113th birthday.