The northernmost station of the Struve Geodetic Arc is located in Fuglenes, Norway.
If one knows the arc length and the central angle, the radius can be easily calculated.
Eratosthenes calculated the arc length by measuring the time it took for caravans to cross the desert.
The angle was determined by measuring the difference between the height of the sun between the latitudes.
What improved was the methodology of measurement.
Map of the Struve Geodetic Arc where red points identify the World Heritage Sites.
Triangulation enabled astronomers and cartographers to accurately measure long distances that stretched for hundreds and thousands of kilometers.
The Struve Geodetic Arc originally consisted of 258 triangles connecting 259 triangulation points.
Some stations also had commemorative monuments erected.
Out of the original 259, 34 stations were collectively inscribed under the UNESCO World Heritage Sites list.
A Struve Geodetic Arc station in Latvia.
Photo credit:Janis U./Wikimedia
A Struve Geodetic Arc station in Hogland, Russia.
Photo credit:Islander/Wikimedia
A Struve Geodetic Arc station in Alta, Norway.
Photo credit:aoiaio/Wikimedia
A Struve Geodetic Arc marker at Tartu Old Observatory in Tartu.
Photo credit:Graham Stone/Flickr
A Struve Geodetic Arc station in Lithuania.
Photo credit:Stefan Krasowski/Flickr
Sources:Wikipedia/Heritage of Astronomy/UNESCO/Euro Geographics
