The term fundamental station is used for special observatories which combine several

space Space is a three-dimensional continuum containing positions and directions. In classical physics, physical space is often conceived in three linear dimensions. Modern physicists usually consider it, with time, to be part of a boundless ...

positioning techniques like

VLBI Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. In VLBI a signal from an astronomical radio source, such as a quasar, is collected at multiple radio telescopes on Earth or in space. T ...

satellite laser ranging Satellite laser ranging (SLR) is a method to measure the distance to satellites in a geocentric orbit. It consists of an astronomical observatory equipped with a laser that sends ultrashort pulses of light. The pulses hit the satellite and boun ...

GPS The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide geol ...

Glonass GLONASS (, ; ) is a Russian satellite navigation system operating as part of a radionavigation-satellite service. It provides an alternative to Global Positioning System (GPS) and is the second navigational system in operation with global cove ...

, etc. They are the basis of

plate tectonic Plate may refer to: Cooking * Plate (dishware), broad, mainly flat vessel commonly used to serve food * Plates, tableware, dishes or dishware used for setting a table, serving food and dining * Plate, the content of such a plate (for example: r ...

analysis, allowing the monitoring of

continental drift Continental drift is a highly supported scientific theory, originating in the early 20th century, that Earth's continents move or drift relative to each other over geologic time. The theory of continental drift has since been validated and inc ...

rates with millimetre accuracies. A fundamental point is the geometric origin of a

geodetic network A geodetic control network is a network, often of triangles, that are measured precisely by techniques of ''control surveying'', such as terrestrial surveying or satellite geodesy. It is also known as a geodetic network, reference network, contro ...

and defines the

geodetic datum A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame, or terrestrial reference frame) is a global datum reference or reference frame for unambiguously representing the positi ...

of a

national survey A national mapping agency (NMA) is an organisation, usually publicly owned, that produces topographic maps and geographic information of a country. Some national mapping agencies also deal with cadastral matters. According to 2007/2/EC European d ...

. Some fundamental stations are an astronomical or satellite geodetic

observatory An observatory is a location used for observing terrestrial, marine, or celestial events. Astronomy, climatology/meteorology, geophysics, oceanography and volcanology are examples of disciplines for which observatories have been constructed. Th ...

. The

geographic latitude In geography, latitude is a geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at the south pole to 90° at the ...

and

longitude Longitude (, ) is a geographic coordinate that specifies the east- west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek lett ...

of the station is precisely determined by methods of astrogeodesy and is chosen as

ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a Surface (mathemat ...

al latitude and longitude at the

Earth ellipsoid An Earth ellipsoid or Earth spheroid is a mathematical figure approximating the Earth's form, used as a reference frame for computations in geodesy, astronomy, and the geosciences. Various different ellipsoids have been used as approximation ...

which is used to calculate the coordinates of the whole network. Also, precise

azimuth An azimuth (; from ) is the horizontal angle from a cardinal direction, most commonly north, in a local or observer-centric spherical coordinate system. Mathematically, the relative position vector from an observer ( origin) to a point ...

s to one or two network points are observed, and are taken over as orientated directions of these network lines. By these procedures, the polar axis of the reference ellipsoid becomes parallel to the

Earth rotation Earth's rotation or Earth's spin is the rotation of planet Earth around its own Rotation around a fixed axis, axis, as well as changes in the orientation (geometry), orientation of the rotation axis in space. Earth rotates eastward, in progra ...

axis, and therefore the

vertical deflection The vertical deflection (VD) or deflection of the vertical (DoV), also known as deflection of the plumb line and astro-geodetic deflection, is a measure of how far the gravity direction at a given point of interest is rotated by local mass anom ...

of the fundamental point is zero. Important fundamental stations include: * Grasse Métrologie Optique (MéO) observatory, France *

Graz Graz () is the capital of the Austrian Federal states of Austria, federal state of Styria and the List of cities and towns in Austria, second-largest city in Austria, after Vienna. On 1 January 2025, Graz had a population of 306,068 (343,461 inc ...

-Lustbühel, Austria *

Herstmonceux Herstmonceux ( , , or ) is a village and civil parish in the Wealden District of East Sussex, England, which includes Herstmonceux Castle. The Herstmonceux Medieval Festival is held annually in August. History The name comes from Anglo-Sax ...

Geodetic Observatory, England * Onsala Space Observatory, Sweden *

Metsähovi Radio Observatory The Metsähovi Radio Observatory is an astronomical observatory in Finland, affiliated with the Aalto University. Its main premises are in Metsähovi, Kirkkonummi, 35 kilometers west of the university's Otaniemi campus. The observatory curre ...

, Finland *

Geodetic Observatory Wettzell The Geodetic Observatory Wettzell is located atop the 616 meter-high mountain Wagnerberg, west of the village Wettzell in the Germany, German Cham (district), district Cham in the Bavarian Forest. Tasks It is operated for the purpose of geode ...

, Germany *

Zimmerwald Observatory The Zimmerwald Observatory () is an astronomical observatory owned and operated by the AIUB, the Astronomical Institute of the University of Bern. Built in 1956, it is located at Zimmerwald, 10 kilometers south of Bern, Switzerland. Numerous com ...

, Switzerland * Goddard Geophysical and Astronomical Observatory, U.S. *

Hartebeesthoek Radio Astronomy Observatory The Hartebeesthoek Radio Astronomy Observatory (HartRAO) is a radio astronomy observatory, located in a natural bowl of hills at Hartebeesthoek just south of the Magaliesberg mountain range, and about 50 km west of Johannesburg, Gauteng, Sout ...

, South Africa * Yarragadee Geodetic Observatory, Australia.Yarragadee: the ‘geodetic supersite’ in the West Australian desert
Geoscience Australia, 2023 Worldwide about 30 fundamental stations are in existence: about 5 in the United States and in

Commonwealth of Independent States The Commonwealth of Independent States (CIS) is a regional organization, regional intergovernmental organization in Eurasia. It was formed following the dissolution of the Soviet Union, dissolution of the Soviet Union in 1991. It covers an ar ...

countries, and 2–3 in South America, Africa, Eastern Asia, Australia and Antarctica. The basic

coordinate system In geometry, a coordinate system is a system that uses one or more numbers, or coordinates, to uniquely determine and standardize the position of the points or other geometric elements on a manifold such as Euclidean space. The coordinates are ...

is the

ITRF The International Terrestrial Reference System (ITRS) describes procedures for creating frame of reference, reference frames suitable for use with measurements on or near the Earth's surface. This is done in much the same way that a Standard (metr ...

reference frame, which is related to the ICRS celestial inertial system by means of very precise

Earth Orientation Parameters In geodesy and astrometry, earth orientation parameters (EOP) describe irregularities in the rotation of planet Earth. EOP provide the rotational transform from the International Terrestrial Reference System (ITRS) to the International Celestial ...

(EOPs), containing

polar coordinate In mathematics, the polar coordinate system specifies a given point in a plane by using a distance and an angle as its two coordinates. These are *the point's distance from a reference point called the ''pole'', and *the point's direction from ...

and

nutation Nutation () is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight, or as an intended behaviour of a mechanism. In an appropriate reference fra ...

parameters. The ITRF data set is revised every 3–5 years, the actual accuracy is in the millimeter area. The ICRS is based on about 500

quasar A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...

s in the far universe, and on some 3000

fundamental star The Catalogue of Fundamental Stars is a series of six astrometric catalogues of high precision positional data for a small selection of stars to define a celestial reference frame, which is a standard coordinate system for measuring positions of ...

s of our

galaxy A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...

. The actual coordinates of the latter ( FK6) were published in 2000 by the

Astronomisches Rechen-Institut The Astronomical Calculation Institute (; ARI) is a research institute in Heidelberg, Germany, with origins dating back from the 1700s. Beginning in 2005, the ARI became part of the Center for Astronomy at Heidelberg University (', ). Previous ...

(ARI) in

Heidelberg Heidelberg (; ; ) is the List of cities in Baden-Württemberg by population, fifth-largest city in the States of Germany, German state of Baden-Württemberg, and with a population of about 163,000, of which roughly a quarter consists of studen ...

References

External links

Fundamentalstation Wettzell, Bavaria

* ttp://www.ari.uni-heidelberg.de/publikationen/vhd/vhd035/fulltext/gifframe.htm Fundamental system FK6, Astronomisches Rechen-Institut (ARI), 1999 Geodesy Astrometry {{geodesy-stub