Measurement of Earth's circumference (Eratosthenes)
Medición de la circunferencia de la Tierra
- Date
- c. 240 BCE · confidence high
- Place
- Alexandria and Syene (Aswan), Egypt
- Credited to
- Eratosthenes of Cyrene
- People
- 👤 Eratóstenes276 BCE–194 BCE
- Field
- Knowledge & symbols
What it is
Calculation of the Earth's size from the difference in gnomon shadow length at Alexandria and Syene at the solstice, and the distance between them, obtaining about 250,000 stadia (an error of under 15%). The first geodetic measurement.
The exact value depends on which stadion was used (157-185 m), hence estimates of error ranging from 1% to 16%.
What it led to
- Mathematical geography and the system of latitude and longitude
- Estimates of global distances that guided, or misled, navigators
- A method of measuring the inaccessible through geometry: a model of quantitative science
- The concept of a scale map of the known world
Built on
- Gnomon and graduated sundialc. 560 BCE
- Sphericity of the Earthc. 350 BCE
- Euclidean axiomatic geometryc. 300 BCE
- Euclidean geometry
- Bematists (professional step-counters)
Made possible
- Map projection with coordinates (Ptolemy's Geography)c. 150 CE
- Al-Ma'mun's meridian arc measurementc. 830
- Al-Biruni's measurement of Earth's radiusc. 1025
- Ptolemy's cartography
- Geodesy
- Voyages of exploration