Al-Farghani
Central Asian astronomer whose summary of Ptolemaic astronomy became a standard textbook in Europe and the Islamic world.
Who or what
Abu'l-Abbas Ahmad ibn Muhammad ibn Kathir al-Farghani (c. 800–870), known in the West as Alfraganus, was a Persian astronomer from Farghana (modern Uzbekistan).
His "Elements of Astronomy" (Kitab fi al-Harakat al-Samawiyah) was a concise summary of Ptolemaic astronomy that became a standard reference.
Why it mattered
Al-Farghani's book was so clear and well-organized that it served as the primary astronomical textbook for centuries in both the Islamic world and Europe.
He accurately calculated the Earth's diameter and the distances to celestial bodies using Ptolemaic methods.
Key works and moments
He calculated Earth's diameter as 6,500 miles (approximate), the circumference as 20,400 miles (remarkably close to modern values).
He described the six planets known at the time, their distances from Earth, and their periods of revolution.
Further detail
His "Elements of Astronomy" covered: celestial spheres, Earth's shape and size, planetary motions, solar and lunar cycles, and astronomical instruments.
The work contained 30 chapters systematically organized for teaching.
Legacy
Translated into Latin by Gerard of Cremona and by John of Seville, it was used by Dante, Columbus, and European astronomers for 500 years.
Columbus used al-Farghani's calculations of Earth's size (though misinterpreting the Arabic miles) to support his westward voyage.
More in Islamic Golden Age
Assembled from the ReLU.chat curated knowledge base. These explanations are concise on purpose; check the sources for anything important.