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Arc of Meridian monument, Hammerfest, Norway. This monument marking the end of Struve's Arc of Meridian, is located at latitude 70 degrees and 40 minutes North. The monument is known as the 'Meridianstotten'. Also known as the Struve Geodetic Arc, the arc was plotted by a geographic survey led by the German astronomer Friedrich Georg Wilhelm Struve (1793-1864). The project took nearly 40 years, from 1816 to 1855. The arc stretches over 2820 kilometres from Hammerfest to the Black Sea. The arc helped establish the size and shape of the Earth, and is on UNESCO's World Heritage list. (KEYSTONE/SCIENCE PHOTO LIBRARY/ROYAL ASTRONOMICAL SOCIETY)