Struve Geodetic Arc

This year I got many stamps as Christmas presents. Many of them are from countries which I had not in my collection before.

A new country is Estonia.

One stamp set is this:

Struve Geodetic Arc (issued 06-05-2011)
- Friedrich Georg Wilhelm Struve (1793-1864)
- Tartu Observatory and the map of Estonia

The Struve Geodetic Arc runs from the Black Sea to the northern coast of Norway. It was built on the initiative of Friedrich Georg Wilhelm Struve and should measure the size and the shape of the earth. The Arc is 2820 km long and is a exceptional example for the cooperation of scientists and monarchs of different countries for a scientific aim. Since 2005 is the Struve Geodetic Arc a UNESCO World Heritage Site of
Belarus (one of four, another is for example Complex of the Radziwill Family at Nesvizh)
Estonia (one of two, the other is the Historic Centre of Tallinn)
Finland (one of seven, another is for example the Fortress of Suomenlinna)
Latvia (one of two, the other is the Historic Centre of Riga)
Lithuania (one of four, another is for example the Historic Centre of Vilnius)
Moldova (the only UNESCO World Heritage Site)
Norway (one of seven, another is for example the Urnes Stave Church)
Russia (one of 25, another is for example Virgin Komi Forests)
Sweden (one of fifteen, another is for example the Laponian Area)
Ukraine (one of seven, another is for example Primeval Beech Forests).