Determination of latitude
Width determination is the abbreviation for calculating astronomical or the latitude of an observation point by the angle measurement after constellations .
Since the prevalence of GPS and other satellite positioning, the term increasingly also includes radio positioning methods .
Fast, proven methods
The oldest - and at the same time the simplest - methods are the measurement of the midday height of the sun and the polar height using the Pole Star . In principle, they only require a single measurement of the elevation angle to the star, provided that the geographical longitude and the exact time are known. If this is not the case, the midday height can be determined as the maximum value of several measurements.
The height of the North Star corresponds to the latitude itself, if one accepts an error of at most 0.7 °. For higher demands, the measurement can be repeated after 12 hours and the two values averaged.
The circummeridian method has also been used since the 18th century , in which a star is measured at the same height on both sides of the meridian. It can also be used to determine time or length and control direction.
More precise methods
More complex, but more precise methods of determining latitude are z. B.
- The astronomical stand line method (English Sumnerline ), in which the heights of two stars are measured and compared with those at the Gisste (assumed) location. The associated stand lines are entered on the nautical chart (or processed digitally) and intersect at the real location of the observer.
- the method of equal heights , in which 3 or more stars are measured and their circles of distance are calculated. They intersect in the place of the observer according to the principle of the arc cut (see also astrolabe and Ni2 astrolabe )
- the Sterneck method , which is particularly good for Sekundentheodolite is
- the Horrebow-Talcott method , which was used to monitor the Earth's polar motion until a few decades ago . Here, pairs of stars are measured with a micrometer at their culmination .
- and other methods of geodetic astronomy , for example the Zinger and Embacher method .
literature
- Karl Ramsayer : Geodetic Astronomy , Handbook of Surveying Volume IIa, 900 p., JB Metzler-Verlag, Stuttgart 1969
- Manfred Meinig: Changes in width of the Potsdam station . In: Astronomical News: A Journal on all Fields of Astronomy . Volume 312 Issue 6, 1991, WILEY-VCH Verlag, pp. 405-411