Astrogeodesy
Under Geodetic Astronomy or Geodetic Astronomy is meant those methods of geodesy and astrometry at which measurements to celestial bodies and other extraterrestrial made goals and the coordinate systems of Spherical Astronomy be used.
The central task is the determination of vertical directions (vertical deviations) and other directions of the earth's space in a fixed reference system . The positions (" places ") of the celestial bodies are set or to be determined in a celestial or celestial coordinate system . The relationship between the two systems is related to the position of the earth in space , especially the earth's rotation .
Possible stars
- Fixed stars , especially precisely measured fundamental stars , and for practical geodesy
- in particular, the Pole Star (Polaris, Polestar)
- the sun (e.g. for the precise orientation of surveying networks )
- bright planets and the earth's moon
In addition, measurements of artificial earth satellites ( satellite geodesy ) and quasars ( cosmic geodesy ) are used, because astronomical geodesy and astrometry overlap somewhat.
Various methods of distance measurement and the most precise time measurement are also used.
Significance of astro-geodetic methods
The goals of these measurements are very diverse:
- Refinement of the terrestrial reference systems
- Determination of the geoid (Astrogeoid, Astr. Leveling )
- Determination of structures and density in the upper crust of the earth
- Stiffening and better accuracy of survey networks
- Orientation of polygons in engineering geodesy
- Overcoming visual obstacles (buildings, forest, lost fixed points )
- Independent navigation through astronomical lines
- Contributions to the spatially fixed coordinate system and to
- ongoing determination of parameters of the earth's rotation .
Measuring instruments
The measuring instruments used are - as in other areas of geodesy - mainly theodolites , tachymeters and quartz clocks , earlier also vacuum pendulum clocks and precise chronometers .
In addition, small to medium-sized special instruments from the field of astronomy and astrometry that work either visually , photographically or optoelectronic :
- Astrolabes (e.g. Ni2 astrolabe from Zeiss, Danjon astrolabe )
- Zenith cameras from 20 to 100 cm focal length and smaller Zenith scopes
- Universal instruments
- Passage instruments (until around 1980) and meridian circles
- Newly developed CCD instruments,
- Stereo comparators for evaluating photographic plates and films; Photogrammetry devices
and (overlapping with satellite geodesy and geophysics ) some of their measurement methods, e.g. B. with
- Satellite cameras
- Kinetheodolite , Gigas theodolite
- special scanners for stars - see z. B. Hipparcos
- Laser - distance measurement to near-earth satellites ( SLR )
- partly pseudoranging with GPS and in future Galileo
- Radio telescopes for VLBI (Very Long Baseline Interferometry )
- Directional and microwave orbit measurements in space travel
- Tide pendulum for earth tides and vertical changes
- Astrogravimetric plumbing deviation determination (see gravity anomaly ).
Well-known scientists
Astrogeodesy owes important developments to u. a. the following researchers (in approximately chronological order):
- Tycho Brahe , James Bradley ,
- Friedrich Argelander , Friedrich Wilhelm Bessel , Carl Friedrich Gauß
- Friedrich Robert Helmert , Johann Palisa , Otto von Struve , Max Wolf ,
- Wilhelm Embacher , Erwin Gigas , Karl Ramsayer
- Helmut Moritz , Albert Schödlbauer , Hellmut Schmid
See also
- Higher geodesy , geoid , gravimetry
- Astronomical navigation , north , positioning , position of the sun ,
- Astronomical refraction , zenith distance , stellar triangulation
- Fundamental point , land surveying , azimuth , plumb line ,
- Atomic time , barycentre , universal time (UT), UTC , CET ,
- Fundamental system (astronomy) , FK4 , FK6 , Hipparcos catalog , ITRF
literature
- Karl Ramsayer : Geodetic Astronomy (= Handbook of Surveying. Vol. 2a). 10th, completely revised and restructured edition. JB Metzler-Verlag, Stuttgart 1970.
- Gottfried Gerstbach : Optimization of astrolabe observations. In: Geoscientific Communications. Vol. 7, 1975, ISSN 1811-8380 , pp. 102-140.
- Albert Schödlbauer : Geodetic Astronomy. de Gruyter, Berlin et al. 2000, ISBN 3-11-015148-0 .
- Bobby Schenk : Astronavigation. Without formulas - practical. 10th, revised edition. Delius Klasing, Bielefeld 2000, ISBN 3-7688-0259-0 .