On a German equatorial mount, the tube can hit the tripod once the object crosses the meridian. The mount then swings the tube over to the other side to keep tracking. In imaging the frame turns by 180° and the object must be re-centred.
Related terms
- Meridian
The imaginary line from north to south through the zenith. When an object crosses it, it reaches its highest point: its culmination, the best time to observe it. The Sun crosses it at solar noon, around 1 pm in winter and 2 pm in summer in France, close to noon or 1 pm in the UK.
- Equatorial mount
A mount with one axis (the right ascension, or polar, axis) parallel to the Earth’s axis of rotation. Once polar aligned, turning that single axis follows the stars, by hand or with a motor. The “German” type, with counterweights, is the most common.
- Culmination
An object’s crossing of the meridian, at the highest point of its path; the best time to observe it. For an object south of the zenith, its altitude then is 90° − latitude + declination. From London (51.5°), the Orion Nebula (−5.4°) culminates at about 33°.
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