How it began
The astronomer Friedrich Georg Wilhelm Struve was working at Dorpat University, now the University of Tartu in Estonia, when he decided to measure an arc along the line of longitude that passed through the university's observatory. The survey was carried out between 1816 and 1855 by Struve and surveyors working under him, with a southern section measured under Carl Tenner. The first point of the arc is at Tartu Observatory, where Struve did much of his research.
How it works
The arc is a chain of survey triangulations. Surveyors measured the angles of connected triangles between fixed station points, so that the distance along the meridian could be calculated across country too large to measure directly. The original arc consisted of 258 main triangles with 265 main station points and ran for more than 2,820 kilometers, from near Hammerfest in Norway to the Black Sea.
What changed first
The survey produced the first accurate measurement of a long segment of a meridian. That helped to establish the exact size and shape of the planet and bore on Isaac Newton's theory that the Earth is not an exact sphere. UNESCO describes it as an important step in the development of earth sciences and of topographic mapping.
What lasted
The work required cooperation among scientists and monarchs of different countries, and UNESCO cites it as an extraordinary example of scientific collaboration. The arc now crosses ten countries: Norway, Sweden, Finland, Russia, Estonia, Latvia, Lithuania, Belarus, Moldova and Ukraine.
Where it stands today
Thirty-four of the original station points, including the one at Tartu Observatory, are protected together as a UNESCO World Heritage site. The listed points lie in all ten countries that the arc crosses. In Estonia the listing ties the arc back to the university observatory where Struve planned and began the work.
