GEM

Abbreviation: German Equatorial Mount. An equatorial mount is one that has one axis of rotation aligned with Earth’s axis of rotation. Once correctly aligned, the mount can track an astronomical object with only one driven axis (RA). By driving the RA axis at the same rate as the Earth’s rotation but in the opposite direction, whatever is in the mounts FOV stays there. Another advantage is there is no rotation visible in the eyepiece or camera FOV as the mount moves with the sky.

The German equatorial mount has the second axis of rotation (declination) at 90° to the RA axis taking the shape of a “T”. One end of the declination axis (usually the upper) has the telescope or camera mounted on it; the other end has a counterweight. The GEM was invented by the German physicist Joseph von Fraunhofer.

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