Struve Geodetic Arc

The Struve Geodetic Arc represents one of the largest and most spectacular attempts to explore and determine the size and shape of the planet, carried out by the astronomer Professor Friedrich George Wilhelm Struve (1793-1864) in 1816-1855. The Geodetic Arc is a chain of survey triangulations, composed of 258 triangles with special marks at the vertexes. It stretches from Hammerfest in Norway to the Izmail on the Black Sea in Ukraine – through 10 countries and over 2,822 km. Precise details of the Earth’s parameters were important not only in geodesy, but also astronomy, navigation and cartography. This is a common transboundary property of Norway, Sweden, Finland, Estonia, Latvia, Lithuania, Russian Federation, Belorussia, Ukraine and Moldova. The Struve Geodetic Arc was inscribed on the World Heritage List in 2005.

Length of arc is 2822 km. Triangulation chain is composed of 258 triangles with special marks at the vertexes. Mean side length of triangle is 27 km, but there are sides with length over 50 km. It passes through modern 10 countries: Norway, Sweden, Finland, Russian Federation, Estonia, Latvia, Lithuania, Belarus, Moldova and Ukraine. The Struve Arc in total consists of 265 points. The largest number of points – 83 is in Finland, while in Lithuania – 18.

Chain of triangulation was surveyed in 1816-1855.

  1. G. W. Struve professor of mathematics and astronomy at the Dorpat (Tartu, Estonia) University was supervising the establishment of geodetic arc. Therefore Geodetic Arc is named after him.
  2. G. W. Struve, a famous astronomer and geodesist, was born in 1793 in Altona town, close to Hamburg, in the family of gymnasium principal. He did not finish studies at the gymnasium and entered Dorpat University in 1808. Struve has graduated from philology faculty after two and a half years and chose a new speciality i.e. astronomy. In 1813 he was granted Master and later Doctor of Philosophy degree for the defended dissertation on the Dorpat observatory geographic location. He was appointed Professor of Mathematics and Astronomy as well as associate of the Dorpat University Observatory. He was one of the first astronomers to measure the stellar parallax and he has discovered a number of double stars. F. G. W. Struve was put in charge of geodetic observations in Livonia (area covering present territories of Estonia and Latvia) in 1816.
  3. G. W. Struve took active part in preparations for building Pulkovo observatory and became its first director in 1839. Struve took care of purchasing astronomic instruments, prepared programs of scientific works, continued research of stars which had been earlier started, determined some astronomic constants and dealt with other astronomic problems. He prepared and published catalogues of double stars coordinates.

Despite full employment in astronomic activities he paid much attention to the geodetic work and research. Struve described his geodetic observations and their results in his two-volumes publication „Geodetic Arc“. He was in charge of some chronometric expeditions to determin longitude difference between Pulkovo and Greenwich. Struve has published over 150 scientific publications, most of them in the field of geodesy and practical astronomy.

Struve became a Correspondent Member of St. Petersburg Academy of Sciences in 1822 and its True Member in 1832. He was among founders of the Russian Geographic Society and Head of the section of Mathematical Cartography. Struve has been delivering lectures on geodesy and astronomy to the officers of military topograpfy for 25 years since 1824.

The purpose for measuring the Struve Geodetic Arc was to determine the form and size of the Earth ellipsoid. The determination of the Earth‘s form and size has been one of the most important problems ever since Aristotle‘s time (4th century BC).

Greek scientist Eratosthenes was first to determine radius of the Earth (3rd century BC). For that purpose the 1° arc length S1 of meridian going through Alexandria and Syena (South Egypt) was determined and from formula 2πR=360°S1 he computed radius R value. He found the Meridian Arc length calculating the travelling speed and travel duration of caravanes crossing the dessert. Latitude difference of arc was found from measured the hight of the Sun on the meridian. Though accuracy of measurements was low but the suggested method for the Earth radius determination was perspective and later on was called method of degree observation. For more accurate determination of the Earth radius, precise geodetic observations were necessary. Triangulation method suggested by the Dutch geodesist V. Snellius in 1615 was applied. Position of points, situated in triangular system, is determined by this method, when angles of triangles are observed as well as a side – the baseline.

After discovering the universe law of gravitation, in 1687 Isaac Newton proved, that form of the earth rotating around its axis should be ellipsoid-like. This meant that the earth ellipsoid curve should increase when moving from equator to the poles.

This theory was proved by Arc measurement expeditions to Peru (1735-1745) and Lapland (1736-1737) organized by the French Academy of Sciences. Measurements in Lapland were carried out by Pierre Maupertuis, assisted by the Swedish physicist Anders Celsius (inventor of a Celsius temperature scale) and mathematician Alexis-Claude Clairaut. Based on the arc measurements performed in France, the definition of the length of metre in 1790 was established as 1/40000000 part of the earth meridian (now it is a length traveller by light in vacuum within 1/299792458 part of a second, 1983). The longest arc measured in the beginning of 19th century was close to 10°. Method of triangulation with astronomic observation allowed to determine more reliably and widely used values of the Earth parameters. However different measurements of arc revealed different values of the Earth ellipsoid parameters. Cartography, navigation, astronomic computations and other scientific research required more precise data on the earth form and size.

During the first half of the 19th century, instruments and methods for measuring improved and new measurements of arc were started. These measurements provided reliable information on the earth ellipsoid form and size. Such measurements were performed in India, but most impressive and largest in extent were the measurements of Struve Geodetic Arc running through 10 countries – from the Arctic Ocean to the Black Sea. Struve Arc measurements in Norway are the most northern point FUGLENAES is 10°40’11,23“, Southern point STARO NEKRASSOWKA - 45°20’02,94“. The difference in geodetic latitude among Arc‘s ends reaches 25°20’08,29“. Struve Geodetic Arc was divided into 12 sections, among 13 astronomic points. 10 baselines were measured for the arc chain.

Struve Geodetic Arc is commemorated by monuments erected in Hammerfest and Nekrasivka, with the inscriptions showing attitude to the establishment of geodetic arc of the countries rulers of that time: tsar of Russia and king of Sweden and Norway.

Measurements of Struve Geodetic Arc were started in 1816 by measuring triangulation network for Vilnius province, conducted mainly for mapping. The South-eastern boarder of the province in those times reached Breslauja, Ashmiany, Lida and grodno. The Southwestern boarder went along the River Nemunas and reached Palanga in the West. The Northern boarder of Vilnius province was very similar to the present national boarder between Lithuania and Latvia. This triangulation network was designed and measurements were organized by the Tsar army officer of estonian descent Carl Tenner. Network observations were completed in 1821. First, he started them on his own initiative, but later after he received approval and guidance from the government. Arc observations were started along the meridian of Vilnius observatory and had continued Northwards and Southwards for almost 35 years. Tenner supervised establishment of triangulation chain from Jekabpils (Latvia) to the mouth of the river Danube. The graduate of Vilnius University, J. Chodzka (1800-1881), assisted Tenner in these observations. Part of the Arc, called „Lithuanian Arc“, from the point BRISTEN (53°35‘) in Latvia to the point BELIN (52°03‘) in Belarus, was completed by Tenner in 1827.

Carl Tenner – a famous geodesist of Russia, was born close to Narva in a poor family. While initially having only elementary education, he gained knowledge of geodesy and cartography during his military service and individually studying geodetic literature himself. He was involved in St. Petersburg and Gulf of Finland Southern shore triangulation in 1812. Having established triangulation in Vilnius province, he continued the same work in the provinces of Courlands, Grodno, Minsk, Volhynia, Podol, Kiev and Bessarabia. He connected the network that he had established himself with the triangulation networks of Eastern Prussia and Austria. Together with his associates, he measured almost half of Struve geodetic arc. Many baselines were measured with Tenner‘s involvement. Part of the astronomic observations in the Southern part of the Arc was done by tenner as well as angular measurements and most computations of geodetic observations. Tenner determined over 4500 triangulation points, more than 700 of them were the first order points. After the trigonometric levelling, he determined the heights of triangulation points and the level difference between the Baltic Sea and the Black Sea. He was in charge of topographic survey along with triangulation activities. Having completed triangulation network in Poland in 1858, he finished his geodetic activities already a General in Tsar‘s army. Struve and the famous German atronomer, director of Königsberg observatory Friedrrich Wilhelm Bessel (1784-1846) greatly valued Tenner‘s observations. K. Tenner was elected a Member of Honour of St. Petersburg Academy of Sciences.

Struve started the arc observations in Livonia by his own. He used to get advices on geodetic observations from F. W. Bessel and C. F. Gauss. Russian government became interested in the Geodetic Arc of 3.5° observations between island of Gogland in gulf of finalnd and Jekabpils in the South. This arc was observed from 1822 to 1831. Astronomic observations at the points of JEKABPILS and HOGLAND were assisted by Professor G. Paucker from Mitau (Jelgava, Latvia). The most complicated observations were those in the Gulf of Finalnd, where the longest triangle side was over 80 km. This chain connected many previous triangulation networks of Livonia, established by Struve in 1816-1819. In 1829, Tenner initiated and connected the arc measurements made by Struve and himself. Struve aimed at extending observed geodetic arc and having succeeded to get governmental support and resources for the continuation of his and Tenner‘s activities, started observations in Finland in 1830. The observations under Struve‘s supervision continued there until 1851. The observations under Struve‘s supervision continued there until 1851. The observations in Finland were complicated due to the forests and swamplands.

The St. Petersburg Academy of Science asked for support from the institutions of Sweden and Norway, in order to extend the triangulation chain to the Northern shores of Norway. The address was answered by the director of Stockholm Royal Observatory N. H. Selander and the director of Christiania (Oslo) Observatory C. Hansteen, who, with the assistance of astronomers Lindhagen and Vagner completed the planned triangulation chain in 1852.

In 1855 the geodetic arc observations were completed. Struve suggested to extend triangulation chain southwards, but due to the political unrest in the region this was not achieved.

The points of the triangulation chain were monumented by the laid fieldstones, bound together with limewash in the dug pit. In the top stone the hole was drilled. The hole was filled with lead. Its centre was marked by a cross. On the ground, the centre was marked by a pole with a driven nail. In the Northen part of the Struve Geodetic Arc often triangulation points were marked by drilling a hole on the solid rochs which were on the ground surface. The baselines of triangulation chain were measured by the baseline apparatus. Tenner‘s apparatus consisted of four iron bars. Length of each bar was 14 feet (about 4,27 m). For the baseline length measurement, bars used to be laid in a line on the balks, while, these on the wooden bucks. Gaps between bars used to be measured by a ruler with vernier, by which using a magnifying glass for the 0.001 inch (0.025 mm) accuracy was achieved. Temperature of the bars was at first measured by bimetallic thermometer, and later by a mercury thermometer. Slope angles used to be measured by eclimeter with a level. Accuracy of 0.1‘ was reached. Relative errors of measured baselines were around 1/300 000. The longest baseline in the Struve arc chain was 11.8 km length. It was measured in 1820 between Pandėlys town and Jokšiai village. It was thelongest baseline of Struve Arc chain. Struve used the baseline apparatus which he himself had improved.

There was a problem in the esatblishment of the Arc triangulation chain related to the different units of length: Russian-English sajen (7 feet), used by Tenner, and Russian-French toise (6 feet), used by Struve.

At the Struve geodetic arc astronomic points by means of celestial bodies observations the astronomic latitude and astronomic azimuth of direction towards the neighbouring point were determined. Temporary astronomic observatories with stone poles for the instruments used to be frequently built for the astronomic observations.

The passage instrument from Vilnius observatory by the famous British mechanic J. Ramsden and astronomic clock by J. Shelton along with other instruments were used at the astronomic points BRISTEN, NEMĖŽIS and BELIN.

It should be stressed that astronomers of the Vilnius observatory actively participated in the above-mentioned astronomic observations. Director of Vilnius observatory Jonas Sniadeckis (1756-1830) and petras Slavinskis determined the astronomic latitude difference between the stations at MEŠKONYS and that of Vilnius observatory. They observed at the Vilnius observatory while K. Tenner with his assistants measured at the point MEŠKONYS. The local time at the points was determined by the astronomic observations. Difference in the local time as well as that of longitude was determined by observing  flashes of burned gunpowder on the hill seen from the both points. 86 flashes were observed during 12 days. By these observations the astronomic longitude of the point MEŠKONYS in relation to Paris was determined as λ=22°58’02,55”. At the same year the astronomic azimuth of direction MEŠKONYS-NEMĖŽIS and latitude at the point MEŠKONYS were determined. The data was used for the initial orientation of the triangulation networks at provinces of Vilnius, Courland and Grodno.

  1. Slavinskis assisted by J. Chodzka determined astronomic latitude of triangulation point EIDINTAIČIAI (around 9 km Northwards from Telšiai) in 1824. George Reichenbach vertical circle, recently obtained by the observatory, was used in order to determine the lattitude. Totally 700 zenith distances to the stars have been measured.

In 1826, director of observatory P. Slavinskis together with astronomer M. Hlušnevičius (1797-1862) and M. Žilinskas determined latituted of the astronomic point BRISTEN. Observations lasted one month. Observations were made a passage instrument. Method suggested by Bessel was used, according to which 36 stars on first vertical were observed. Local time and clock run were determined by the passage instrument. This method of latitude determination was also used in other astronomic points of Lithuanian Arc.

A temporary astronomic observatory was established in Nemėžis astronomic point, 6 km Southern from Vilnius observatory and first observations were made in 1826. Nemėžis astronomic latitude was determined by M. Hlušnevičius and J. Chodzka in 1827. The passage instrument was used. Observations lasted from August 2nd to October 13th. During 48 nights, 86 stars were observed for the latitude determination.

In 1827, tenner, j. Chodzka and M. Žilinskas conducted the astronomic observations in BELIN point.

Longitude of NEMĖŽIS point was computed in 1828 trough the triangulation network from Dorpat observatory.

Azimuth of the side NEMĖŽIS-MEŠKONYS was determined using the passage instrument in 1832. Repeated observations of the three brightest stars of the Little Bear were made by astronomer of Vilnius observatory M. Hlušnevičius. Struve computed the azimuth. He and Tenner highly valued the observations made by M. Hlušnevičius. In responce to the application sent by Struve and Tenner to St. Petersburg, M. Hlušnevičius was awarded St. Stanislav IV rank order and a diamond ring by the Russian Tsar.

Longitude of Dorpat was re-determined in 1854. Struve was in charge of the chronometric expedition between Dorpat and Pulkovo. 31 chronometers were transported 10 times.

Latitude of Nemėžis was redetermined by the director of Vilnius observatory Jegoras Sableris (1810-1865) in 1855. The G. Reichenbach‘s vertical circle from Vilnius observatory was used.

The Tsar‘s army soldiers helped Tenner to perform observations, built the points and temporary astronomic observatories and guarded them during the most of geodetic and astronomic activities.

It should be noted that Struve‘s observations were very accurate. This was proved by the unbelievable accuracy of angular and linear observations in the 19th century. Error of angle measurement was 0,57“ in Livonia, 0,87“ in Finland, where the conditions for observation were the most complicated, and 0,68“ in the Lithuanian Arc. Accuracy of the Arc measurement was 1/232390 (4 mm per km).

The accuracy of the Struve‘s arc triangulation chain was strictly checked after its connection to the Prussian triangulation network in 1832-1834. Triangulation networks of different countries were connected due to the efforts by F. W. Bessel, after measuring almost 200 km length triangulation chain between Trunco and Klaipėda, which ended triangulation network sides established by Tenner. After comparison of the common side length, computed from baselines measured in Palanga and Königsberg, differences were bellow 0,15 m, and relative errors were lower than 1/200 000.

In the 1841, F. W. Bessel has computed and published the Earth ellipsoid parameters based on the observation results of the connected triangulation networks. These have been used in many European countries.

By using Struve Geodetic Arc observation data, the meridian arc of 1° was computed for each of the twelve parts of the Struve arc: 1° length of the Northern part was 111,589 km; of the Southern part – 111,230 km; of the two Lithuanian parts – 111,373 km and 111,292 km respectively.

The Struve geodetic arc has a significant scientific role. It was a longest arc measured at that time, running from Northern cape of Norway to the Black Sea. The Struve‘s arc was 450 km longer than arc of William Lambton and George Everest measured in India almost at the same time (1800-1843). The Struve‘s arc was the first one crossing the territories of several countries. Activities of the Arc establishment demonstrated excellent collaboration abilities of scientist from different countries in solving problems related to research of the earth form. 100 years have passed since establishment of the Struve Arc until similar multinational measurements took place in East Africa.

The Struve arc was the most accurate arc of that time. Once more the exceptional accuracy of the geodetic measurements, achieved in the 19th century should be stressed. The best available geodetic and astronomic instruments, some of them especially produced for this purpose, were used for measurements. During the observation process the special methods were elaborated. New method suggested by Struve was applied for measurements of angles, and method by Bessel for determination of the astronomic latitude. The astronomic longitude of MEŠKONYS point was extraordinary determined by using burned gunpower.

Struve Arc being distinguished for its length and observation accuracy, established new possibilities for the improvement of the Earth ellipsoid form and size determination. Bessel was first to use the data of the not yet completed Struve Arc for determination of the new ellipsoid parameters. Result achieved by Struve ang his colleagues were used in all the subsequent computations of the Earth ellipsoid parametres, based on triangulations. They were used in the course of the century, until methods of satellite geodesy for the determination of the ellipsoid parametres were elaborated.

The improved data on the form of the earth ellipsoid were important not only in geodesy, but also in astronomy, navigation, cartography. Because of this new data, navigation on the seas was improved, distances to the celestial bodies were re-determined, and better cartographic projections were developed for the accurate mapping.

The arc was important for determination of the Earth form and its dimensions, for improving of the geodetic observation methods, for developing practical precise geodetic activities. In the course of establishment of the Struve geodetic arc, solution of scientific problems was harmonised with practical tasks. Along with expanding triangulation networks, up to the 20th century the Struve Arc chain was used as geodetic reference for mapping of territories that the Arc was running through. The Arc chain of triangulation had a similar application in Lithuania too.

The active participation of astronomers from the Vilnius University in the measurements and observations of the Lithuanian part of the arc and the successful results improved their attitude for the problems solution in the field of geodetic astronomy and for the improvement of the instrumentation of the University astronomic observatory. Geodetic activities resulted in establishment of the Department of Geodesy at Vilnius University in 1826. The first head of the department was M. A. Antanas Šakinis (Antoni Szahin). The department existed until the University was closed in 1831.

The problem of the Earth form and size determination has always attracted interest of famous geodesists, astronomers and mathematicians. The scientific goal of achieving accurate arc observations influenced development of the new methods and instruments for angular, linear and astronomic observations.

The Struve Arc measurements are important achievements, from the scientific and cultural point of view. Close cooperation in working out scientific, political, cultural and financial problems was going on among different scientists of many countries: geodesists, astronomers, and producers of instruments.

The Struve Geodetic Arc is one of the greatest scientific and technological achievements of the 19th century. This object manifests unique international connection of science and culture.

Nowadays satellite geodesy methods are used for determination and improvement of the earth ellipsoid parameters. These methods can assure centimetre accuracy. GRS 80 (Geodetic reference System 1980) ellipsoid, determined by the USA scientists, is recommended to use by International Association of Geodesy. It‘s major semi-axis is 6378137 m, while minor semi-axis is shorter than the major one by 21384, 6859 m. Following the decision of Lithuanian Government, ellipsoid GRS 80 by was introduced for use in geodetic activities along with introduction of a new coordinate system in 1994.

The National Land Survey of Finland and the Finnish Geodetic Institute suggested to commemorate the Struve Geodetic Arc as UNESCO‘s World Heritage property in 1993. The International Federation of Surveyors (FIG) and the International Institution for the History of Surveying & Measurement supported this initiative in 1994. Appropriate resolution was adopted during FIG congress at Melbourne in 1994.

 The suggested method for commeration of the heritage property required that every involved country locate at least two Struve Geodetic Arc points, and arranged everything according to the national requirements of heritage institutions. All countries involved collaborated in locating, investigating and commemorating sites of historical measurements since 1994. These sites are located using available geodetic observation data by means of the recent measurement methods as well as satellite geodesy.

34 selected points of the Struve Geodetic Arc, as one of the world‘s foremost scientific and technical acievements, are introduced to the international society. From one to six points represent the following countries: Norway – 4, Sweden – 4, Finland – 6, Russia – 2, Estonia – 3, Latvia – 2, Lithuania – 3, Belarus – 5, Moldova – 1, Ukraina – 4. Other Arc points are patronized at national level.

Every country has selected its most famous sites: for example, Tartu observatory in Estonia and Alatornio church in Finalnd. These are the only two sites where unchanged remaining buildings were used for the observations. Arc‘s terminal points are also listed for the conservation: FUGLENAES at the Arctic Ocean and STARO NEKRASSOWKA at the Black Sea.

The National Land Service at the Ministry of Agriculture and the Institute of geodesy of Vilnius Gediminas Technical University have suggested commemoration of the three Struve Geodetic Arc points, namely GIREIŠIAI, MEŠKONYS and PALIEPIUKAI, which have already belonged to the National Geodetic Network. The suggestion was approved by the State Commission for Cultural Heritage and the Department of Cultural Heritage under the Ministry of Culture of the Republic of Lithuania.

Inscription into the World Heritage List

Ten countries shared the preparation to inscribe the Struve Geodetic Arc on the World Heritage List. This project was coordinated by the National Land Survey of Finland. The National Survey Organizations in all countries gave been in charge of the preparation under supervision of the National Cultural Heritage Institutions.

Many international organizations, suc as the International Federation of Surveyors, the International Association of Geodesy, the International Astronomical Union and euroGeographics, have been active in supporting the preservation of the Struve Arc and advocating its nomination for the World Heritage List.

Nomination was submitted to the World Heritage Committee in January 2004. The World Heritage Committee inscribed the Struve Geodetic Arc into the World Heritage List in July 2005. The World Heritage Committee stated that the Struve Geodetic Arc meets three criteria for the inscription into the World Heritage List:

- the first accurate measuring of a long segment of a meridian, helping in the establishment of the exact size and shape of the world exhibits an important step in the development of the Earth sciences. It is also an extraordinary example for interchange of human values in the form of scientific collaboration among scientists from different countries. It is at the same time an example for collaboration between leaders of different countries, for scientific benefits;

- the Struve Geodetic Arc is undoubtedly an outstanding example of technological ensemble – presenting the triangulation points of the measuring of the meridian, being the non movable and non tangible part of the measuring technology;

- the measuring of the Arc and its results are directly associated with men wondering about his world, its shape and size. It is linked with Sir isaac Newton‘s theory that the World is not an exact sphere.

This Arc complements to the variety of the World Heritage. The Struve Geodetic Arc is a forst cross boarder international nomination in the World Heritage List proposed by ten countries. This is one of the first nominations of a very great significance to the development of geodesy, cartography and astronomy sciences.

The official ceremony to mark the inscription of the Struve Geodetic Arc into World Heritage List was held at one of Lithuanian measurements spots – Meškonys. On 16 June 2006 there gathered honorable guests from other countries in the territories of which there are located other Struve Geodetic Arc measurement spots. There were also representatives from embassies, state, scientific, professional and nongovernmental organizations. The assembled listened to the word of the President of Lithuania, conveyed by the President‘s Adviser, other congratulation words by the authorities from the Ministries of Agriculture and Culture. The most significant was the moment when World Heritage Committee Chairman, Ambassador Ina Marčiulionytė handed down to the authorities of Ministry of Agriculture the Certificate, which says that since July 2005 Struve Geodetic Arc has been inscribed into the World Heritage List.