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mountingThe structure that supports an astronomical telescope, designed so that the telescope may be pointed at almost every part of the heavens, preferably without forcing an observer into awkward positions. All telescope mountings must therefore be constructed so that the tube can turn about two axes at right angles. There are two main types: the equatorial mounting, with one axis parallel to the Earth's axis, and the altazimuth mounting, with one axis vertical. Since high magnifications exaggerate any movement, the support must be rigid. In addition, because the Earth is turning through 0.25° per minute, means must be provided to move the telescope smoothly in the opposite direction; this counterbalances the diurnal motion of a star and keeps it in the field of view.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006