woensdag 22 januari 2014

Ukraine, Struve Geodetic Arc

The Struve Arc is a chain of survey triangulations stretching from Hammerfest in Norway to the Black Sea, through 10 countries and over 2,820 km. These are points of a survey, carried out between 1816 and 1855 by the astronomer Friedrich Georg Wilhelm Struve, which represented the first accurate measuring of a long segment of a meridian. This helped to establish the exact size and shape of the planet and marked an important step in the development of earth sciences and topographic mapping. It is an extraordinary example of scientific collaboration among scientists from different countries, and of collaboration between monarchs for a scientific cause. The original arc consisted of 258 main triangles with 265 main station points. The listed site includes 34 of the original station points, with different markings, i.e. a drilled hole in rock, iron cross, cairns, or built obelisks.

The first accurate measuring of a long segment of a meridian, helping to establish the exact size and shape of the world, exhibits an important step in the development of earth sciences. Since around 500 BC it had been known that the Earth was not flat, but of some spherical shape. In the 3rd century BC, the surveying technique and theory for determining the size of the Earth was developed by Eratosthenes. This theory remained in use until the era of satellite geodesy. Eratosthenes's theory, using length measurement and angles determined by star observations, made it possible to determine the size of the Earth, while the measurements themselves were still not accurate, mainly owing to inadequate methods and equipment.
In the 17th century better measuring equipment was developed, together with a new method using triangulations. According to this method, a much shorter line could be measured accurately, while the long distances were covered by a chain of triangles. These triangles each spanned several hundred kilometres, with each of their sides (base lines) as long as 100 km and each triangle in the chain having one common base line with at least one other triangle and two common corners (station points) with another triangle.
The triangulation method helped to establish in the 1730s and 1740s the true shape of the Earth, by means of long arcs in Peru and Lapland. The problem of the size of the Earth remained unsolved and had become even more complex, as it was known that it was not a perfect sphere. The different early arcs in France, Peru, Lapland, Italy, South Africa and Austria had various shortcomings that did not allow for an accurate solution of this issue. The defeat of Napoleon, followed by the Congress of Vienna and the decision in 1815 to establish agreed international boundaries in Europe, required accurate mapping. These needs were strongly felt in Russia, where Tsar Alexander I provided the astronomer Wilhelm Struve with all the resources for his project for a new long geodetic arc. This can be seen as the first step for the development of modern geodetic framework and topographic mapping.
A very long arc, completed in 1840, had been measured in India by Lambton and Everest, and a shorter arc in Lithuania by Carl Tenner. Struve, who was working at the Dorpat University in modern Estonia, decided that the arc he would establish would follow a line of longitude (meridian) passing through the observatory of the university. The new long arc, later to be known as the Struve Arc, was finally createded by connecting earlier, shorter arcs to the southern one measured by Tenner, and their extension to the north and south. The arc covered thus a line connecting Fuglenæs near Hammerfest in the far north, along 2,800 km, with Staro-Nekrasowka, near Ismail, on the Black Sea shores.
The World Heritage site consists of 34 of the original station points established by Struve and his colleagues between 1816 and 1851 - four points in Norway, four in Sweden, six in Finland, one in Russia, three in Estonia, two in Latvia, three in Lithuania, five in Belarus, one in Moldova and four in Ukraine. These marks take different forms: small holes drilled in rock surfaces, and sometimes filled with lead; cross-shaped engraved marks on rock surfaces; solid stone or brick with a marker inset; rock structures (cairns), with a central stone or brick, marked by a drilled hole; single bricks; and specially constructed 'monuments' to commemorate the point and the arc.
The Struve Geodetic Arc is an extraordinary example of interchange of human values in the form of scientific collaboration among scientists from different countries, as well as an outstanding example of a technological ensemble.

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