# Stellar triangulation > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Stellar_triangulation > Markdown URL: https://mediated.wiki/source/Stellar_triangulation.md > Source: https://en.wikipedia.org/wiki/Stellar_triangulation > Source revision: 1227294497 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations. Please help improve this article by introducing more precise citations. (December 2009) (Learn how and when to remove this message) **Stellar triangulation** is a method of [geodesy](/source/Geodesy) and of its subdiscipline [space geodesy](/source/Space_geodesy) used to measure Earth's geometric shape. Stars were first used for this purpose by the Finnish astronomer [Yrjö Väisälä](/source/Yrj%C3%B6_V%C3%A4is%C3%A4l%C3%A4) in 1959, who made [astrometric](/source/Astrometric) photographs of the night sky at two stations together with a lighted [balloon](/source/Balloon) probe between them. Even this first step showed the potential of the method, as Väisälä got the [azimuth](/source/Azimuth) between [Helsinki](/source/Helsinki) and [Turku](/source/Turku) (a distance of 150 km) with an accuracy of 1″. Soon the method was successfully tested by [ballistic](/source/External_ballistics) rockets and for some special [satellites](/source/Satellites). Adequate [computer programs](/source/Computer_program) were written for - the astrometric reduction of the photographic plates, - the [intersection](/source/Intersection_(set_theory)) of the "observation planes" containing the stations and the targets, - and the [least-squares adjustment](/source/Least-squares_adjustment) of stellar-terrestrial networks with [redundancy](/source/Data_redundancy). The advantages of stellar triangulation were the possibility to cross far distances (terrestrial observations are restricted to approx. 30 km, and even in high mountains to 60 km), and the independency of the Earth's gravity field. The results are azimuths between the stations in the [stellar-inertial navigation system](/source/Stellar-inertial_navigation_system), despite no direct [line of sight](/source/Line-of-sight_propagation). In 1960, the first appropriate [space probe](/source/Space_probe) was launched: [Project Echo](/source/Project_Echo), a 30 m diameter [balloon satellite](/source/Balloon_satellite). By then the whole of [Western Europe](/source/Western_Europe) could be linked together geodetically with accuracies 2–10 times better than by classical [triangulation](/source/Triangulation_(surveying)). During the late 1960s, a global project was begun by [H.H. Schmid](/source/H.H._Schmid) (Switzerland) to connect 45 stations all over the continents, with distances of 3000–5000 km. It was finished in 1974 by precise reduction of some 3000 stellar plates and network adjustment of 46 stations (2 additional ones in [Germany](/source/Germany) and the Pacific, but without the areas of [Russia](/source/Russia) and [China](/source/China)). The mean accuracy was between ±5 m (Europe, USA) and 7–10 m (Africa, Antarctica), depending on weather and infrastructure conditions. Combined with [Doppler](/source/Doppler_effect) measurements (such as from [*Transit*](/source/Transit_(satellite))) the global accuracy was even 3 m. This is more than 20 times better than previously, because the [gravity field](/source/Earth's_gravity) up to 1974 couldn't be calculated better than 100 meters between distant [continents](/source/Continent). The use of [stars](/source/Star) as a reference system was expanded in the 70s and early 80s for continental networks, but then the [laser](/source/Laser) and [electronic](/source/Electronics) [distance measurements](/source/Distance_measurement) became better than 2 m and could be carried out automatically. Nowadays some similar techniques are carried out by [interferometry](/source/Interferometry) with very distant radio [quasars](/source/Quasar) ([VLBI](/source/VLBI)) instead of optical satellite & star observations. The geodetic connection of [radio telescopes](/source/Radio_telescope) is now possible up to mm–cm precision as published periodically by the community. This global project group was founded in 2000 by Harald Schuh (Munich/TU Vienna) and some dozen research projects worldwide, and is now a permanent service of [International Union of Geodesy and Geophysics](/source/International_Union_of_Geodesy_and_Geophysics) (IUGG) and [International Earth Rotation and Reference Systems Service](/source/International_Earth_Rotation_and_Reference_Systems_Service) (IERS). The photographic observations as done in 1959–1985 are considered irrelevant now because of their expense, but they have led to a revival of electro-optical techniques like [CCD](/source/Charge-coupled_device). ## See also - [Figure of the Earth](/source/Figure_of_the_Earth) - [Fundamental station](/source/Fundamental_station) - [Triangulation](/source/Triangulation) - [Trilateration](/source/Trilateration) - [Satellite geodesy](/source/Satellite_geodesy) - [Satellite geodesy#Optical triangulation](/source/Satellite_geodesy#Optical_triangulation) - [PAGEOS](/source/PAGEOS) satellite - [Satellite laser ranging](/source/Satellite_laser_ranging) (SLR) - [Stellar parallax](/source/Stellar_parallax) for distances to stars ## References - A.Berroth, W.Hofmann: *Kosmische Geodäsie*(*Cosmic Geodesy*) (356 p.), G.Braun, Karlsruhe 1960 - [Karl Ledersteger](/source/Karl_Ledersteger): "Astronomische und Physikalische Geodäsie ([Erdmessung](/source/Geodesy))", *[Handbuch der Vermessungskunde](https://en.wikipedia.org/w/index.php?title=Handbuch_der_Vermessungskunde&action=edit&redlink=1)*, [Wilhelm Jordan](/source/Wilhelm_Jordan_(geodesist)), [Otto Eggert](/source/Otto_Eggert) and [Max Kneissl](https://en.wikipedia.org/w/index.php?title=Max_Kneissl&action=edit&redlink=1) ed., Volume V, (870 S., espec. §§ 2, 5, 13), J.B.Metzler, Stuttgart 1968. - [Hellmut Schmid](/source/Hellmut_Schmid): *Das Weltnetz der Satelitentriangulation*. Wiss. Mitteilungen [ETH Zurich](/source/ETH_Zurich) and *Journal of Geophysical Research*, 1974. - Klaus Schnädelbach et al.: Western European Satellite Triangulation Programme (WEST), 2nd Experimental Computation. Mitteilungen Geodät.Inst. Graz 11/1, Graz 1972 - Nothnagel, Schlüter, Seeger: Die Geschichte der geodätischen [VLBI](/source/Very_Long_Baseline_Interferometry) in Deutschland, Bonn 2000. ## External links - [NOAA's geodesy photo library](https://photolib.noaa.gov/Collections/Geodesy) --- Adapted from the Wikipedia article [Stellar triangulation](https://en.wikipedia.org/wiki/Stellar_triangulation) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Stellar_triangulation?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.