Astronomical positioning
As astronomical location determination is traditionally called the determination of geographical latitude and longitude by means of astronomical angle and time measurements .
The name “location determination” is somewhat misleading because it is not the location itself that is determined , but its plumb line . The term became common in geography and scientific expeditions about 200 years ago because at that time it was the only method of measuring an unknown position to an accuracy of about 1 km without outside help. Actually it is a matter of determining the astronomical latitude and longitude , i.e. H. a determination of the direction of the physical vertical direction relative to the rotating earth axis and the astronomical meridian plane of Greenwich (or another observatory ).
The reason why the AO is not a position determination in the actual sense, but only a direction measurement , is the deviation from the perpendicular . This deflection of the perpendicular (or the vertical geoid = sea level) from its mathematical position is a consequence of the mass distribution on and within the earth's body . In the high mountains it can be up to 50 ", which would mean an apparent spatial error of 1.5 kilometers (1 arc second in the center of the earth corresponds to about 31 m on the earth's surface).
Special items
The methods of astronomical positioning are discussed in more detail in the following articles:
- Width determination (latitude)
- Determination of longitude (geographical longitude)
- Time determination (local sidereal time or local time)
See also
literature
- Wolfgang Torge : Geodesy (3rd edition), de Gruyter-Verlag, Berlin 2001
- Karl Ramsayer : Geodetic Astronomy , Volume IIa of the manual of surveying JEK , JB Metzler-Verlag, Stuttgart 1969
- Franz Ackerl : Geodesy and Photogrammetry , Volumes 1 and 2, Fromme 1950 and 1956
- Sigmund Günther: Physical Geography , Göschen Collection (Leipzig), ca.1910