Al-Battani: The Astronomer Copernicus Cited by Name

Who He Was

Abu Abdallah Muhammad ibn Jabir ibn Sinan al-Battani (858–929 CE), known in the West as Albatenius or Albategnius, was an Arab astronomer and mathematician from Harran in present-day Turkey. He is considered one of the greatest astronomers of the medieval period.

What He Did

Astronomical precision: Al-Battani produced measurements of extraordinary accuracy using improved instruments and methodology. His determination of the solar year as 365 days, 5 hours, 46 minutes, and 24 seconds differs from the modern value by only 2 minutes and 22 seconds, the most accurate measurement of the solar year in the medieval period.

Correcting Ptolemy: Al-Battani demonstrated that the direction of the sun's apogee (the point at which it is furthest from the Earth) was not fixed as Ptolemy had assumed but was gradually shifting. This was a significant correction to the Ptolemaic model.

Trigonometry: Al-Battani introduced the use of sines in trigonometric calculations, replacing the chord function used by Ptolemy. He developed the concept of the cotangent and produced the first table of cotangents. These contributions transformed trigonometry into a more functional computational tool and became the foundation for European trigonometry.

The precession of the equinoxes: Al-Battani refined the measurement of the precession of the equinoxes to 54.5 arc seconds per year, close to the modern value of 50.3 arc seconds.

The European Recognition

Al-Battani was cited by name in De Revolutionibus by Copernicus, one of the most important books in the history of science. Tycho Brahe, Galileo, and Kepler all referenced his work. His astronomical tables were used by European astronomers for centuries.

The Latinisation of his name (Albatenius) again obscured his identity. His Opus Astronomicum (the Latin translation of his Kitab al-Zij) was published in Nuremberg in 1537 and used by European astronomers well into the 17th century.

Copernicus did not merely cite al-Battani in passing. He used al-Battani's observational data as foundational material for his heliocentric model, the same model that is credited with initiating the scientific revolution. The observational foundations of that revolution were measured by a Muslim astronomer working in 9th-century Syria.