Telescope mount
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A telescope mount is a mechanical structure which supports a telescope. Telescope mounts are designed to support the mass of the telescope and allow for accurate pointing of the instrument. Many sorts of mounts have been developed over the years, with the majority of effort being put into systems that can track the motion of the stars as the Earth rotates with a single motion.
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[edit] Alt-az mounts
Main article: Altazimuth mount
The earliest types of mounts are today known as altitude-azimuth, or alt-az systems. The name refers to the way the system allows the telescope to be moved in altitude, up and down, or azimuth, side to side, as separate motions. One limitation of this mount is that the telescope's field-of-view rotates at varying speed as the telescope tracks, whilst the telescope body does not, thus causing problems with astro-photography, for example. This type of mount is used in practically all modern big telescopes, and has also become popular with inexpensive commercial and hobby constructions.
[edit] Equatorial mounts
Main article: Equatorial mount
The introduction of the equatorial mount displaced most alt-az systems for many serious users for several centuries. By tilting the horizontal base of an alt-az system up until it is parallel to Earth's equatorial plane, the azimuth rotation then swings the telescope in an arc that follows the stars as they move across the sky due to Earth's rotation. By attaching a simple clockwork mechanism to this axis, the equatorial system makes long observation easy. Also the telescope's field-of-view does not rotate, which all combined make these simpler tools to use in e.g. astro-photography.
Equatorial mounts come in different shape, most common forms include German Equatorial Mount (GEM in short), equatorial fork mount, and equatorial platform.
[edit] Transit
For Transit telescopes there is a special mount, whereby the telescope point always along the meridian, but its elevation can be varied.
[edit] Fixed
Some telescopes are entirely fixed, for example the Zenith telescopes that point only straight up.
Another special fixed system is used on solar telescopes, where the telescope itself is fixed, but light comes in via two flat mirrors, one of which tracks the sun across the sky.
[edit] Hexapod-Telescope
Instead of the classical mounting using two axles, the mirror is supported by six extendable struts (hexapod). This configuration allows moving the telescope in all six spatial degrees of freedom and also provides a strong structural integrity.
