In astronomy, there are two major groups of instrumental mounts : The alt-azimuth and equatorial. The first usually equip all small initiation instruments. Easy to implement, intuitive to use and requires no special knowledge. However, with these mounts, it is also easy to find an object to lose because it is obliged to act on both axes to follow. The altazimuth mounts will therefore used only as visual (the DOBSON telescopes are part of this category). When one team an evolving astronomical instrument, it immediately switches to the second family, the equatorial. Fitted with polarfinder or not, they can be set so that we can follow a star by acting only on one axis, the time axis (the second, the declinaison, being used for tracking corrections).

This time axis, if it is equipped with a stepper motor controlled by an electronic quartz rigorous can practice without embarrassment astrophotography. The famous setting that allows the equatorial mount to develop its full potential in monitoring quality to compensate for the Earth's rotation is called the station establishment.

I practiced this setting each night early for a little over ten years on a German mount polarfinder. So this is the mount type that I know very well the process which I have detailed the main phases in the diagram above.

The quality of the stationing on a German mount polar finder for an observer in the Northern Hemisphere is directly influenced by the position of the north celestial pole relative to the stars as it is to match a pattern lasered in the viewfinder with the actual position of the pole star whose validity is not definitive.

The long precession extending a cycle of 41,000 years causing a steady movement of the celestial North Pole among the stars. In this long circular course, the representative of the celestial pole star changes repeatedly over the millennia. In this perspective, we can deduce that the celestial north pole was incarnated once, around 3000 BC, the Thuban star in the constellation Draco. Then, in a slow slide that lasted 5000 years, North Celestial Pole is now close to the pole star.

The annual value of the displacement is 50.290966 arcseconds per year or 1 arcdegrees every 72 years. This movement is not harmless because it means the German equatorial mount polarfinder is actually becoming obsolete in the space only two decades !

Stationing a german mount

03/15

 

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Arnaud FIOCRET
 

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