German mount
The German mount (also equatorial mount) is an equatorial mount for astronomical telescopes . It was already around 1610, shortly after the invention of the telescope, the Jesuit Christoph Grienberger at the Vatican Observatory for solar observations of his friar Christoph Scheiner (co-discoverer of sunspots) developed.
In principle, it consists of two mutually perpendicular axes that are equipped with roller bearings in modern mountings . The right ascension or hour axis must point exactly to the celestial pole and is therefore parallel to the earth axis . The second axis is the declination axis . It points to the celestial equator and allows the telescope to be swiveled into the correct declination in the sky .
The hour axis has a compact axis cross in which the declination axis is stored. The telescope tube is attached to one end of the declination axis and a counterweight to balance the tube weight is located at the other end . The hour axis bearing is always loaded with the tilting moment of both, therefore the two roller bearings of the hour axis should have a large distance from one another. The mount is mostly driven by worm wheels and stepper motor controls. The accuracy with which the mount can track the telescope to an object under observation depends on the precision with which the worm wheel was manufactured and on its diameter.
In commercial mounts for amateur telescopes , a polar finder telescope is often integrated into the tubular hour axis.
The mount usually has 2 additional adjustment axes. By rotating around the vertical axis, the north direction is set as the zero point of the azimuth . The horizontal axis is used to adapt to the pole height (= geographical latitude of the observer). Both axes are only required for transportable telescopes and are often a structural weak point. In observatories and other permanently installed observation instruments , more stable devices are used for adjustment .
Advantages and disadvantages of the German mount
The German mount is suitable for telescopes with long and short tubes. Statically it is better suited for middle geographic latitudes.
The compact design facilitates transport and assembly as well as the construction of stable mounts by amateurs.
Like the English mount , the German mount must also be balanced with a counterweight, since the telescope's center of gravity is not at the intersection of the hour axis and the declination axis. The counterweight makes the mount more susceptible to vibrations.
With long telescopes - depending on the geographical latitude of the location and the declination of the observed object - it can happen that the telescope tube hits the mount when passing through the meridian . The telescope must then be turned from the east to the west. Since the image field rotates by 180 °, photographic recordings across the meridian passage are not possible under these circumstances.
Individual evidence
- ↑ The presentation essentially follows: Herwin G. Ziegler: Teleskopmontierungen and their electrical devices. In: Günter Dietmar Roth (Hrsg.): Handbook for Sternfreunde (Volume 1). Springer-Verlag, Berlin, Heidelberg 1989 (special edition for Weltbild Verlag, Augsburg), pp. 93–100