A telescope mount is a mechanical structure which supports a

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...

. 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 In physics, motion is the phenomenon in which an object changes its position with respect to time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed and frame of reference to an observer and m ...

of the

fixed stars In astronomy, fixed stars ( la, stellae fixae) is a term to name the full set of glowing points, astronomical objects actually and mainly stars, that appear not to move relative to one another against the darkness of the night sky in the backgro ...

as the Earth rotates.

Fixed mounts

Fixed telescope mounts are entirely fixed in one position, such as

Zenith telescope A zenith telescope is a type of telescope that is designed to point straight up at or near the zenith. They are used for precision measurement of star positions, to simplify telescope construction, or both. A classic zenith telescope, also know ...

s that point only straight up and the

National Radio Astronomy Observatory The National Radio Astronomy Observatory (NRAO) is a federally funded research and development center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc. for the purpose of radio a ...

's Green Bank fixed radio ' horn' built to observe

Cassiopeia A Cassiopeia A (Cas A) () is a supernova remnant (SNR) in the constellation Cassiopeia and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. The supernova occurred approximately away within the Milky Way ...

Fixed altitude mounts

Fixed-altitude mounts usually have the primary optics fixed at an

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

angle while rotating horizontally (in

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematical ...

). They can cover the whole sky but only observe objects for the short time when that object passes a specific altitude and azimuth.

Transit mounts

Transit mounts are single axis mounts fixed in azimuth while rotating in altitude, usually oriented on a north-south axis. This allows the telescope to view the whole sky, but only when the Earth's rotation allows the objects to cross (''transit'') through that narrow north-south line (the meridian). This type of mount is used in

transit telescope In astronomy, a transit instrument is a small telescope with extremely precisely graduated mount used for the precise observation of star positions. They were previously widely used in astronomical observatories and naval observatories to meas ...

s, designed for precision astronomical measurement. Transit mounts are also used to save on cost or where the instruments mass makes movement on more than one axis very difficult, such as large

radio telescope A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency ...

Altazimuth mounts

Altazimuth, altitude-azimuth, or ''alt-az mounts'' allow telescopes to be moved in altitude (up and down), or azimuth (side to side), as separate motions. This mechanically simple mount was used in early telescope designs and until the second half of the 20th century was used as a "less sophisticated" alternative to equatorial mounts since it did not allow tracking of the night sky. This meant until recently it was normally used with inexpensive commercial and hobby constructions. Since the invention of digital tracking systems, altazimuth mounts have come to be used in practically all modern large research telescopes. Digital tracking has also made it a popular telescope mount used in

amateur astronomy Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomers ...

. Besides the mechanical inability to easily follow celestial motion the altazimuth mount does have other limitations. The telescope's field-of-view rotates at varying speed as the telescope tracks, whilst the telescope body does not, requiring a system to counter-rotate the field of view when used for

astrophotography Astrophotography, also known as astronomical imaging, is the photography or imaging of astronomical objects, celestial events, or areas of the night sky. The first photograph of an astronomical object (the Moon) was taken in 1840, but it was no ...

or other types of astronomical imaging. The mount also has blind spot or "zenith hole", a spot near the zenith where the tracking rate in the azimuth coordinate becomes too high to accurately follow equatorial motion (if the elevation is limited to +90 degrees).Bill Keel's Lecture Notes - Astronomical Techniques - Telescope Mountings
/ref>

Alt-alt (altitude-altitude) mounts

Alt-alt mounts, or altitude-altitude mounts, are designs similar to horizontal equatorial yoke mounts or Cardan suspension gimbals. This mount is an alternative to the altazimuth mount that has the advantage of not having a blind spot near the zenith, and for objects near the

celestial equator The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. This plane of reference bases the equatorial coordinate system. In other words, the celestial equator is an abstract proj ...

the field rotation is minimized.La montatura alt-alt (The alt-alt mount), article in italian
/ref> It has the disadvantage of having all the mass, complexity, and engineering problems of its equatorial counterpart, so is only used in specialty applications such as satellite tracking. These mounts may include a third azimuth axis (an ''altitude-altitude-azimuth mount'') to rotate the entire mount into an orientation that allows smoother tracking.

Equatorial mounts

The equatorial mount has north-south "polar axis" tilted to be parallel to Earth's polar axis that allows the telescope to swing in an east-west arc, with a second axis perpendicular to that to allow the telescope to swing in a north-south arc. Slewing or mechanically driving the mount's polar axis in a counter direction to the Earth's rotation allows the telescope to accurately follow the motion of the night sky. Equatorial mounts come in different shapes, include

German equatorial mount An equatorial mount is a mount for instruments that compensates for Earth's rotation by having one rotational axis, the polar axis, parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras. The ...

s (GEM in short), equatorial fork mounts, mixed variations on

yoke A yoke is a wooden beam sometimes used between a pair of oxen or other animals to enable them to pull together on a load when working in pairs, as oxen usually do; some yokes are fitted to individual animals. There are several types of yoke, u ...

or cross-axis mounts, and

equatorial platform An equatorial platform or equatorial table is an equatorial telescope mount in the form of a specially designed platform that allows any device sitting on it to track astronomical objects in the sky on an equatorial axis. They are used to give equ ...

s such as the

Poncet Platform A Poncet Platform or Poncet mount is a type of equatorial platform (a telescope mount that adds an additional ''polar axis'' to non- equatorial mounts) that uses a simple polar pivot and an inclined plane. The motion of the mount allows any dev ...

. Tilting the polar axis adds a level of complexity to the mount. Mechanical systems have to be engineered to support one or both ends of this axis (such as in fork or yoke mounts). Designs such as German equatorial or cross axis mounts also need large counter weights to counterbalance the mass of the telescope. Larger domes and other structures are also needed to cover the increased mechanical size and range of movement of equatorial mounts. Because of this, equatorial mounts become less viable in very large telescopes and have been pretty much replaced by altazimuth mounts for those applications.

Hexapod-Telescope

Instead of the classical mounting using two

axes Axes, plural of '' axe'' and of '' axis'', may refer to * ''Axes'' (album), a 2005 rock album by the British band Electrelane * a possibly still empty plot (graphics) See also * Axess (disambiguation) *Axxess (disambiguation) Axxess may refer to ...

, the mirror is supported by six extendable

strut A strut is a structural component commonly found in engineering, aeronautics, architecture and anatomy. Struts generally work by resisting longitudinal compression, but they may also serve in tension. Human anatomy Part of the functionality o ...

s ( Stewart-Gough platform). This configuration allows moving the telescope in all six spatial degrees of freedom and also provides a strong structural integrity.

References

{{Reflist Telescopes