Sunday, October 23, 2016

Struve Geodetic Arc: The 2,820 Km Line That Produced The First Accurate Measurement of The Earth’s Size

From the northern coast of Norway to the southern coast of Ukraine runs a chain of survey triangulation points that together forms the Struve Geodetic Arc. It stretches from Hammerfest (Norway) on the shores of the Arctic Ocean to Nekrasivka (Ukraine) by the Black Sea, a distance of 2,820 km, snaking in and out of numerous territories, that today belong to ten different countries. The arc was established by the German-born Russian scientist Friedrich Georg Wilhelm von Struve, who undertook a thirty-nine-year-long survey, between 1816 and 1855, to determine the shape and size of the earth. The survey yielded the first accurate measurement of a meridian arc, which in turn allowed the first precise measurement of the earth’s diameter.

The determination of the size and shape of the earth was one of the most important problems for natural philosophers since the ancient times. In the 2nd century BC, Greek astronomer and mathematician, Eratosthenes, developed a method to determine the radius of the earth by measuring a portion of a meridian arc and comparing that length to the corresponding angle subtended at the Earth’s center. 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. Although the accuracy of his measurements were low, Eratosthenes was able to calculate the earth’s radius with an accuracy of 1%. For two thousand years, Eratosthenes’ “method of degree observation” remained the most promising method of determining the size of the earth. What improved was the methodology of measurement.

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