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Collection Finding Our Place in the Cosmos: From Galileo to Sagan and Beyond

Astronomical Innovation in the Islamic World

Between the 8th and 15th centuries Islamic astronomers produced a wealth of sophisticated astronomical work. Largely through the Ptolemaic framework, they improved and refined the Ptolemaic system, compiled better tables and devised instruments that improved their ability to make observations. The extensive contributions of Islamic astronomy also exposed some weaknesses in the Ptolemaic and Aristotelian systems.

Expounding and Teaching

al-Farghani (died after 861), known in the west as Alfraganus, wrote Elements of Astronomy on the Celestial Motions around 833. This textbook provided a largely non-mathematical presentation of Ptolomy's Almagest, updated with revised values from previous Islamic astronomers. The work circulated widely throughout the Islamic world and was translated into Latin during the 12th century.  It became the primary resource that European scholars used to study Ptolemaic astronomy.

This book was largely responsible for the emergence of the Greek astronomical system of Ptolemy in the West. It circulated in several Latin editions and was widely studied in Europe between the 12th and 17th centuries.

In other cases, like the work of Ibn al-Hatheym's  Doubts on Ptolomey, went far beyond translating and transmitting knowledge to developing an extensive critique of Ptolomey, and turned the mathematical models into a physical representation of movement in the heavens.

Refining and Expanding on Ptolemy

In The Book of the Fixed Stars, Al- Sufi combined Ptolemy's work of mapping constellations with Arabic astronomical traditions.  Written around 964 the book contains extensive illustrations of each constellation from both the terrestrial perspective, looking up from Earth, and the inverse, as the constellation would look from outside the sphere of the fixed stars.

Al-Sufi's drawings became the canonical representations of these constellations. In Europe his works were translated and widely circulated. Even today, we use many of the star names that he recorded in the book.

The Book of the Fixed Stars documented more constellations and more stars in those constellations than ever before.  These include some of the first recordings of what we would later understand to be another galaxy. The star on the right side of the belt of Andromeda is not actually a star as Al-Sufi originally thought, but is instead one of only two galaxies visible to the naked eye. He had recorded an observation of what we would later come to know of as the Andromeda Galaxy.

The Source of Classical Astronomy in the West

The frontispiece of this copy of his most famous work shows the Islamic astrologer, Jafar Ibn Muhammad Abu Mashar al-Balkhi (805(?)-886), also known as Abu Mashar, holding an armillary sphere. It's important to remember that our contemporary notions that associate astronomy with science and astrology with superstition are poor frames of reference to import into our understanding of the past. In Abu Mashar's time, contemplating the meaning of stars' movements and how they impacted future human events was a valid and empirical practice.

Aside from Abu Mashar's work in astrology, his translations of Greek texts, in particular Aristotle's works, played an essential role in disseminating Aristotle's ideas in the Islamic world and later in Europe. His work was translated from Arabic into Latin in the 12th century and was held in great esteem by Medieval and Renaissance intellectuals.

This frontispiece for this translation of al-Farghani's Elements of Astronomy shows him ('Alfraganus is his Latinized name) teaching a student. It is a potent representation of how Islamic astronomers played a pivotal role teaching Europe astronomy. Written between 833 and 857, al-Farghani's work is a thorough, readable, and non-mathematical summary of Ptolemaic astronomy. The popularity of translations of his work more than half a century later testifies to its importance.  Breuis ac perutilis co[m]pilatio Alfragani . . . totu[m] id continens quod ad rudimenta astronomica est opportunum. c861/1493, frontispiece.
Above, is an example of one of the Constellations described in the Book of the Fixed Stars -- in this case, the constellation Andromeda. In hind sight, this drawing is particularly significant because the star on the right side of Andromeda's belt is actually one of only a few galaxies visible to the naked eye. Suwar al-kawakib. (Book of the Fixed Stars) 946/ 1417. African and Middle Eastern Division
The frontispiece of this copy of his most famous work shows the Islamic astrologer, Jafar Ibn Muhammad Abu Mashar al-Balkhi, known as Abu Mashar, holding an armillary sphere (a device used to predict the movements of the stars). Here he is presented teaching the use of the tool. De magnis conjunctionibus (On great conjunctions) 1515. Rare Book and Special Collections Division.