Durchmusterung
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Durchmusterung is a German word for a systematic survey of objects or data.
In astronomy, it is the usual name for the first comprehensive astrometric star catalogue of the whole sky, processd by the Bonn Observatory (Germany) in the middle of the 19th century, named the Bonner Durchmusterung.
Today the term Durchmusterung includes not only stars but also the search for other celestial objects. Special tasks are the celestial scanning in electromagnetic wavelengths which are shorter or longer than light waves.
The decadal work of the Bonner Durchmusterung (abbreviated by BD) tabulates the positions and apparent magnitudes of approximately 300,000 stars to apparent magnitude 9–10. It was the basis for an excellent star atlas (some 100 pages) and for the AGK and SAO catalogues of the 20th century. The BD star numbers are still used and allow the correlation of this pioneering work with modern projects.
Many astronomical projects — from studies of celestial mechanics and the solar system, up to the nascent field of astrophysics — were essentially supported by Atlas and data of the Bonner Durchmusterung. But some decades later the positional accuracy began to be insufficient for more exact projects. Further the BD could not cover the whole sky, because far southern stars are not visible from Germany.
So the scientific community decided to supplement the Southern Sky by two additional astrometric surveys which should be carried out by observatories located at the Southern hemisphere:
- Córdoba, Argentina, and
- Cape Town, South Africa
The Cordoba Durchmusterung (abbreviated CD) was made visually — similar to the former BD), but the Cape Photographic Durchmusterung (CPD) was conducted by the new photographic technique, which just before was shown to have sufficient accuracy.
Similar to the BD numbers, the southern stars are identified by CD and CPD numbers.
To establish a more exact reference system for the Bonner Duchmusterung, in the late 19th century the astronomers and geodesists began to work on a Celestial Fundamental Co-ordinate System, based on the Earth's rotation axis, the vernal equinox and the Ecliptic plane. This astrometric project led to the Fundamental Catalogue of the Berlin observatory and was used as an exact coordinate frame for the BD and AGK. It was modernized in the 1920s (FK3, mean accuracy ±1"), up to the present FK6 as the latest step of cosmic geodesy (accuracy 0.1"). Together with radioastronomical measurements the FK6 accuracy is now better than ±0.1".
Parallel to this, some astrometric satellites were planned to revolve round the Earth. The most important result of these developments was the Hipparcos space probe which scanned 108,000 stars over the whole sky by a network of thousands of CCD cross profiles and led to three very accurate star catalogues:
- Hipparcos Catalogue (108,000 stars, average accuracy ±0.003")
- Tycho Catalogue (1 Million stars, with accuracy ±0.03"), and
- Tycho II Catalogue (> 1 Mill.?) which was improved for double star effects and other small systematic errors.
In the next decade a further step is planned using a future satellite, Gaia. The Gaia catalogue plans to have at least 10 times more stars than Tycho II, with an apparent magnitude limit of 13 or fainter. Therefore will include a sufficient number of stars of our Galaxy to make future projects more relevant for the extreme accuracy of modern space science.
