The Struve Geodetic Arc is a series of survey triangulation points that stretch from Hammerfest in Norway to the Black Sea, passing through ten countries and covering over 2,820 kilometers (1,750 miles). This chain provided the first accurate measurement of a meridian arc, which is a line of longitude on Earth.

The chain was created and used by Friedrich Georg Wilhelm von Struve, a German-born Russian scientist, between 1816 and 1855. His work helped determine the exact size and shape of Earth. At the time, the chain passed through only three countries: Norway, Sweden, and the Russian Empire. The first point of the Arc is located at Tartu Observatory in Estonia, where Struve did much of his research. The triangulation chain includes 258 main triangles and 265 key measurement points. The northernmost point is near Hammerfest in Norway, and the southernmost point is near the Black Sea in Ukraine.

In 2005, the chain was added to the UNESCO World Heritage List because of its importance in geodesy and its role in showing international scientific cooperation. The World Heritage site includes 34 commemorative plaques or obelisks from the original 265 main station points. These points were marked with drilled holes in rock, iron crosses, cairns, and other structures. This World Heritage site spans ten countries, the second-highest number among UNESCO sites after the Ancient and Primeval Beech Forests of the Carpathians and Other Regions of Europe.

Measurements of the 30° Meridian Arc between 1816 and 1852, as well as descriptions of geodetic, topographical, and map-making work in the Balkans from the 19th century until the early 20th century by the Russian Empire’s military forces, are detailed in the book Astronomy, geodesy and map-drawing in Moldova since the middle ages till the World War I.

Chain

• Fuglenes in Hammerfest (70°40′12″N 23°39′48″E / 70.67000°N 23.66333°E / 70.67000; 23.66333)
• Raipas in Alta (69°56′19″N 23°21′37″E / 69.93861°N 23.36028°E / 69.93861; 23.36028)
• Luvdiidcohkka in Kautokeino (69°39′52″N 23°36′08″E / 69.66444°N 23.60222°E / 69.66444; 23.60222)
• Baelljasvarri in Kautokeino (69°01′43″N 23°18′19″E / 69.02861°N 23.30528°E / 69.02861; 23.30528)

• "Pajtas-vaara" (Tynnyrilaki) in Kiruna (68°15′18″N 22°58′59″E / 68.25500°N 22.98306°E / 68.25500; 22.98306)
• "Kerrojupukka" (Jupukka) in Hattula, Finland (60°43′48″N 22°18′12″E / 60.73000°N 22.30333°E / 60.73000; 22.30333)
• "Kerrojupukka" (Jupukka) in Hattula, Finland (60°43′48″N 22°18′12″E / 60.73000°N 22.30333°E / 60.73000; 22.30333)

• "Pajtas-vaara" (Tynnyrilaki) in Kiruna (68°15′18″N 22°58′59″E / 68.25500°N 22.98306°E / 68.25500; 22.98306)
• "Kerrojupukka" (Jupukka) in Hattula, Finland (60°43′48″N 22°18′12″E / 60.73000°N 22.30333°E / 60.73000; 22.30333)
• "Kerrojupukka" (Jupukka) in Hattula, Finland (60°43′48″N 22°18′12″E / 60.73000°N 22.30333°E / 60.73000; 22.30333)

• "Pajtas-vaara" (Tynnyrilaki) in Kiruna (68°15′18″N 22°58′59″E / 68.25500°N 22.98306°E / 68.25500; 22.98306)
• "Kerrojupukka" (Jupukka) in Hattula, Finland (60°43′48″N 22°18′12″E / 60.73000°N 22.30333°E / 60.73000; 22.30333)
• "Kerrojupukka" (Jupukka) in Hattula, Finland (60°43′48″N 22°18′12″E / 60.73000°N 22.30333°E / 60.73000; 22.30333)

• "Pajtas-vaara" (Tynnyrilaki) in Kiruna (68°15′18″N 22°58′59″E / 68.25500°N 22.98306°E / 68.25500; 22.98306)
• "Kerrojupukka" (Jupukka) in Hattula, Finland (60°43′48″N 22°18′12″E / 60.73000°N 22.30333°E / 60.73000; 22.30333)
• "Kerrojupukka" (Jupukka) in Hattula, Finland (60°43′48″N 22°18′12″E / 60.73000°N 22.30333°E / 60.73000; 22.30333)

• "Pajtas-vaara" (Tynnyrilaki) in Kiruna (68°15′

Results

In 1858, the Earth's flattening was measured as 1 part in 294.26. The Earth's equatorial radius was measured as 6,378,360.7 meters (20,926,380 feet).

In 2005, scientists used satellite navigation to repeat the measurement. The new flattening was found to be 1 part in 298.257 222 101, and the equatorial radius was measured as 6,378,136.8 meters (20,925,646 feet).

A survey in 1740 estimated the Earth's flattening as 1 part in 178, with an equatorial radius of 6,396,800 meters (20,986,900 feet).

Northernmost point: Hammerfest (Fuglenes): 70° 40' 11.23″ N
Southernmost point: Ismail (Staro-Nekrassowka): 45° 20' 02.94″ N

Difference in Geodetic Latitude: 25° 20' 08.29″
Distance in kilometers: 2,821.853 ± 0.012