- Geodetic astronomy
**Geodetic astronomy**is the application of astronomical methods into s and technical projects ofgeodesy .The most important topics are:

* Establishment of geodetic datum systems (e.g.ED50 ) or at expeditions

*apparent places of stars, and theirproper motion s

* precise astronomical navigation

* astro-geodeticgeoid determination and

* modelling the rock densities of the topography and ofgeological layers in thesubsurface

*Satellite geodesy using the background ofstar s (see alsoastrometry andcosmic triangulation )

* Monitoring of theEarth rotation and polar wandering

* Contribution to thetime system of physics andgeosciences Important

**measuring techniques**are:

*Latitude andlongitude determination bytheodolite s, tacheometers,astrolabe s orzenith camera s

*time andstar position s by observation ofstar transit s, e.g. bymeridian circle s (visual, photographic or CCD)

*Azimuth measurements

** for the exact orientation ofgeodetic network s

** for mutual transformations between terrestrial and space methods

** for improved accuracy by means of "Laplace point s" at special fixed points

*Vertical deflection measurements and their use

** in geoid determination

** in mathematical reduction of very precise networks

** for geophysical andgeological purposes (see above)

* Modernspatial methods

**VLBI with radio sources (quasar s)

**Astrometry of stars byscanning satellites likeHipparcos or the future Gaia.The

of these methods depends on the instrument and its spectral wavelength, the measuring or scanning method, the time amount (versus economy), the atmospheric situation, theaccuracy stability of the surface resp. the satellite, on mechanical andtemperature effects to the instrument, on the experience and skill of the observer, and on the accuracy of the physical-mathematical models.Therefore the accuracy reaches from 60" (navigation, ~1 mile) to 0,001" and better (a few cm; satellites, VLBI), e.g.:

*angle s (vertical deflections andazimuth s) ±1" up to 0,1"

*geoid determination & height systems ca. 5 cm up to 0,2 cm

* astronomical lat/long and star positions ±1" up to 0,01"

*HIPPARCOS star positions ±0,001"

*VLBI quasar positions andEarth's rotation poles 0,001 to 0,0001" (cm...mm)**See also***

Astronomy ,stellar triangulation ,spherical trigonometry

*Satellite ,space techniques ,electro-optics , CCD

*Triangulation ,tacheometer ,passage instrument

*Astro navigation ,Karl Ramsayer

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