Polar cradle
A polar cradle is an accessory part of astronomical instruments . With it, an azimuthal mount can be converted into an equatorial mount.
function
The polar cradle inclines the main axis of the mount so that it is aligned parallel to the axis of the celestial equator . Due to the inclination of the main axis, the telescope only has to be tracked in the hourly axis ( right ascension ) in order to compensate for the earth's rotation and to keep the observation object in the field of view. The rotation of the image field that occurs with azimuthal mounting is avoided, which enables astrophotographic recordings with a long exposure time.
construction
The polar cradle consists of a base plate and a second plate, the inclination of which is adjustable. The optimal angle of inclination for observing celestial objects corresponds to the latitude of the observation location. The inclination is adjusted by turning a threaded rod and fixed with clamping screws. For precise adjustment of the celestial pole , the base plate can be aligned horizontally using a second setting option. The polar cradle is placed on a tripod or a column. The azimuthal mount with the telescope is placed on the cradle .
commitment
The polar cradle is used in amateur astronomy in order to be able to take longer exposed sky images with a relatively simple azimuthal mount (e.g. fork mount). The counterweight required for the equatorial mount is not required. The disadvantage of the construction is that the entire telescope structure can become more unstable and susceptible to vibrations.