Al Battani: the 9th-century Muslim star of astronomy

Astronomy has always held a special place in Islamic education. The Holy Quran has over 1,100 verses touching upon the creation of the universe, the alignment of the stars and other ideas that were later proven right upon scientific inquiry. 

Astronomical observation in the Islamic Golden Age, while largely neglected by the western world, reached far beyond what many scholars throughout history have given it credit for. Since mathematics is an integral part of astronomy, Islamic scholars with a strong understanding of spherical trigonometry and algebra were able to excel in the science of celestial objects.

Born in the mid-ninth century in Harran (38 km southeast of Türkiye’s Urfa Province), known by the Romans as Carrhae, Abu Abdallah Mohammad ibn Jabir ibn Sinan al Raqqi al Harrani al Sabi al Battani, also known as Al Battani, rose to a position of renown among European astronomers in later centuries and has even been dubbed the "Ptolemy of the Arabs."

Al Battani’s family belonged to the Sabian sect — a religious sect of star-worshippers native to his hometown. Although Al Battani was a Muslim and did not follow the Sabian religion, he took advantage of the knowledge of the Sabian sect, which had produced many outstanding astronomers and mathematicians thanks to the desire of its followers to serve their religion. In addition to his access to Sabian wisdom, Al Battani was the student of his father, Jabir ibn Sinan al Harrani, a famous scientific instrument-maker in the Sabian society — paving the way for his astronomical breakthroughs.

His strikingly accurate estimates of the length of the year and his original innovations in advancing and enlightening the science of astronomy through trigonometric calculations were achieved at a time before modern astronomical equipment, let alone telescopes. These advances led him to become known as one of the greatest astronomers of all time. Commenting upon the errors he encountered in the work of other astronomers, Al Battani reveals why he was striving to “perfect and confirm” the science of astronomy: 

“After having lengthily applied myself to the study of this science, I have noticed that the works on the movements of the planets differed consistently with each other and that many authors made errors in the manner of undertaking their observation, and establishing their rules. I also noticed that with time, the position of the planets changed according to recent and older observations; changes caused by the obliquity of the ecliptic, affecting the calculation of the years and that of eclipses. Continuous focus on these things drove me to perfect and confirm such a science.”

According to Baron Carra de Vaux, a French orientalist who published memoirs of his travels in the Middle East, the merit of Al Battani was his pioneering use of trigonometry in his calculations. Unlike Ptolemy, who relied on geometrical methods, Al Battani placed more importance on empirical results and employed trigonometrical methods — an important advance that allowed him to calculate 54.5" per year for the precession of the equinoxes. He also obtained 23° 35' for the inclination of the ecliptic. His measurements are said to have been more accurate than those of Copernicus, likely related to the fact that his observations were made from a more southerly latitude. 

In addition to introducing several trigonometric relationships, the Muslim master of astronomy also revealed that the farthest distance between the Sun and the Earth varies and that, as a result, annular eclipses of the Sun are possible — as are total eclipses. His groundbreaking book, “Kitab az Zij,” which was translated into Latin by Plato of Tivoli in 1116 CE, was used by famous astronomers such as Copernicus and Galileo. 

The book, which comprises 57 chapters, first deals with the division of the celestial sphere into the signs of the zodiac and the degrees of celestial bodies. This introduction is followed by a list of necessary mathematical tools, including sexagesimal fractions and trigonometric functions. 

The rest of the book consists of justifications of his own views based on personal observations, in addition to elucidations of a large number of different astronomical problems and calculations of the motions of the sun, moon and five planets. It also includes instructions on how to read his tables, debates around the construction of a sundial and an evaluation of the construction of a number of astronomical instruments. Finally, the book not only catalogues a total of almost 500 stars, but also refines the existing values for both the seasons and for the length of the year — calculating the latter as 365 days, five hours, 46 minutes and 24 seconds.

During his scientific journey, Al Battani used an incredibly wide variety of instruments, from astrolabes, tubes, a gnomon divided into twelve parts, and a celestial globe with five armillaries (which he was believed to have created), to angle rulers, a mural quadrant, and sundials, both vertical and horizontal. 

Al Battani made many of his major astronomical observations in the ancient city of Raqqa, in northern Syria, where he lived from the 870s until 919. After resolving a dispute on behalf of the people of Raqqa in Baghdad, he died during his return to Raqqa in Qas al-Jiss, near Iraq’s Samarra, in 929 CE.

Known by Latinised versions of his name — Albatenius, Albategnius or Albategni — among his mediaeval European admirers, Al Battani continues to be revered for his astonishing scientific breakthroughs, which not only enlightened the science of astronomy for his posthumous students, but also left an invaluable legacy of knowledge that greatly contributed to the field of astronomy as we know it.