Al-Ma'mun's meridian arc measurement
Medición del grado de meridiano de al-Mamún
- Date
- c. 830 · confidence medium
- Place
- Plain of Sinjar, Nineveh, Iraq
- Credited to
- Astronomers of al-Ma'mun (sons of Musa ibn Shakir, Sanad ibn Ali)
- Field
- Cosmos & Earth
⚠️ Disputed: the sources disagree.
What was discovered
Two teams set off in opposite directions across the plain of Sinjar, measuring with ropes until the altitude of the Pole Star changed by one degree, and obtained 56⅔ Arabic miles per degree. It was the first direct geodetic measurement of a meridian arc.
The result (about 111.8 km per degree depending on the mile adopted) is very accurate, but the exact value of the Arabic mile used is uncertain. Another measurement was made between Tadmur (Palmyra) and Raqqa.
What it led to
- Earth-size value used by Islamic geography
- distance calculations in al-Khwarizmi's maps
- tradition of observational geodesy