Al-Farghani

Abu al-Abbas Ahmad ibn Muhammad ibn Kathir al-Farghani was born around 800 CE in Farghana, a city in the fertile Fergana Valley of present-day Uzbekistan. Little is known of his early life, but he came to prominence in Baghdad during the reign of Caliph al-Mamun, joining the celebrated House of Wisdom where the greatest scientific minds of the Islamic golden age gathered.

Al-Farghani became one of the most important astronomers of the ninth century. He participated in the famous geodetic expedition ordered by al-Mamun to measure the circumference of the Earth — an achievement that placed the Islamic world far ahead of its contemporaries in empirical science. The measurements were conducted in the flat plains of northern Mesopotamia, and the results were remarkably accurate.

His most celebrated work, the Kitab fi Jawami Ilm al-Nujum (Elements of Astronomy), was a comprehensive summary of Ptolemy's Almagest, written in clear and accessible Arabic prose. This text went far beyond mere summary: al-Farghani corrected several of Ptolemy's values, recalculated planetary distances and sizes, and presented the material in a more organized and teachable form. The work was translated into Latin twice in the twelfth century — by John of Seville and by Gerard of Cremona — and became a foundational textbook in European universities well into the Renaissance.

Christopher Columbus reportedly used al-Farghani's calculations of Earth's circumference, though he confused Arabic miles with shorter Italian miles, leading to his famous underestimate of the distance to Asia.

Al-Farghani also supervised engineering works, including the construction of a Nilometer at Fustat in Egypt. He died around 870 CE. His synthesis of Ptolemaic astronomy with Islamic observational data became the standard astronomical reference for two continents.