Struven Ketju

‘STUOR-OIVI’ – a UNESCO World Heritage Site 68º40’57’’ north latitude and 22º44’45’’ east longitude One of the six Finnish station points forming part of the Struve Geodetic Arc protected as a UNESCO World Heritage Site is located at the summit of Stuorrahanoaivi in Enontekiö. The Struve Geodetic Arc is a triangulation chain stretching from the Black Sea to the Arctic Ocean that was laid down in the 1800s to determine the shape of the Earth. The Arc is named after the German-born astronomer F.G.W. Struve. The Struve Geodetic Arc was measured between 1816 and 1855. The measurements, which yielded surprisingly accurate results, gave rise to a chain of 265 station points stretching from Izmail on the Black Sea to Hammerfest in Norway. 83 station points were measured in Finland. Wilhelm Struve and his expedition employed triangulation and astronomical positioning as measuring methods, the objective being to measure the flatness at the poles. The measurements proved that the length of a meridian degree at the Black Sea is about 400 metres shorter than at the Arctic Ocean. UNESCO’s World Heritage Committee added the Struve Geodetic Arc to the World Heritage List in July 2005. The documentation, put together by the National Land Survey of Finland, comprised a joint application by 10 countries. In addition to being the first protected site of a scientific and technological nature, the Struve Geodetic Arc is also the first cultural site that extends across several countries. A total of 34 station points are now protected. The measurements at the summit of Stuorrahanoaivi were carried out between 1850 and 1852. The point was marked with two crosses carved into the stone. Norway made Stuorrahanoaivi part of its own triangulation network in 1895 and installed a metal bolt at the site. The surroundings at the point are still as open and suitable for observations as in Struve’s days. The station point at Stuorrahanoaivi has been one of Finland’s main geodetic station points since the measurements for the Struve Geodetic Arc. A first class triangulation point was set in almost the same spot in 1970, only 7.6 metres north of the point Struve measured. Stuorrahanoaivi 2 and Mustaviiri island are the only Struve points in Finland included in the World Heritage list that cannot be reached by road. Stuorrahanoaivi is a good 10 kilometre walk away from both the Enontekiö to Kautokeino road and the road between Muonio and Kilpisjärvi. At the time of the measurements bearing his name, Wilhelm Struve headed the Pulkovo observatory in Russia. In the 1850s, when the measurement work was in its later stages, he was already over 50 years old, and he charged the Swede Daniel Georg Lindhagen (who later married Struve’s daughter) with completing the astronomical measurements in Lapland. Nils Hagvin Selander, another Swede, also made a name for himself with Struve’s measurements in Lapland, as he was responsible for the measurements between Bäljatz-vaara in Norway and Tornio. From triangulation to satellite-based measurement Before it was possible to use satellite technology in surveying, surveys were based on measurements of the angles of a triangulation network formed from observation sites. The sides of the triangles, i.e. baselines, were determined using invar wires up to the introduction of distance-measuring equipment in the 1960s. The measurement findings of the Struve Geodetic Arc have been used for many scientific purposes, and the Arc functioned as a model for triangulation technology up to the advent of satellite measurements. In Finland, the Struve Geodetic Arc connected the triangulation chains in the north and south for more than a century, before National Land Survey triangulation chains covered the whole country in the 1960s. Nowadays, measurements are carried out with GPS instruments using satellite positioning, which are accurate down to a few centimetres. The ease of taking measurements has developed even more rapidly than their accuracy, as it is no longer necessary to have an expedition to carry the measuring devices. In 2004, advanced VRS technology (Virtual Reference Station) was introduced in Finland. In this, the base-station network is made up of fixed GPS-base stations that transmit information via a GSM-network. Thus only one portable device is needed for taking measurements. 3 The other protected points in Finland that are part of the Struve Geodetic Arc are Alatornio church; Aavasaksa; Oravivuori in Korpilahti, Central Finland; Porlammi in Lapinjärvi; and Mustaviiri in the Gulf of Finland. In Finland the Struve Geodetic Arc is also referred to as the Russo-Scandinavian meridian arc. The Struve Geodetic Arc, which begins in the Danube Delta, enters Finland north of Suursaari island and runs to the east of Loviisa, and through the Lahti and Jyväskylä regions, from where it continues via Kajaani, Oulu, Tornio and Muonio to Hammerfest in Norway. .

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