equatorial mounting

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equatorial mounting:

see telescopetelescope,
traditionally, a system of lenses, mirrors, or both, used to gather light from a distant object and form an image of it. Traditional optical telescopes, which are the subject of this article, also are used to magnify objects on earth and in astronomy; other types of
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equatorial mounting

equatorial mounting

A telescope mounting in which one axis (the polar axis) is parallel to the Earth's axis of rotation, while the second axis (the declination axis) is at right angles to it. Its great advantage is that when the telescope is clamped in declination, and the polar axis is driven to turn once in 24 hours in the opposite direction to the Earth's rotation, any star will remain stationary in the field of view. Until recently almost every large telescope was equatorially mounted, but the constantly changing stresses involved in swinging possibly hundreds of tonnes of asymmetrically shaped material about an inclined axis mean that the mounting must be extremely strong and hence extremely costly, so as a result many telescopes are now constructed with a computer-controlled altazimuth mounting.

There are several types of equatorial mountings, some being shown in the illustration. In the fork mounting the telescope swings in declination about an axis carried on two prongs of a fork; the fork itself rotates about a shaft that is the polar axis. In the yoke (or English) mounting the polar axis is in the form of a long frame with a bearing at each end. The telescope swings in declination about an axis between the sides of the frame. This mounting is simple, very rigid, and needs no counterpoise weights; the polar region is, however, inaccessible. The horseshoe mounting is a modification of the fork and yoke mountings: the upper end of the polar axis frame is made into a horseshoe shape to accommodate the telescope tube; the polar region may then be observed. Many of the giant reflectors use this exceptionally stable mounting. In the German mounting the declination axis is carried as a tee on the top end of the polar axis. The telescope is carried on one end of the declination axis and there is a counterpoise on the other end.

The drive mechanism for the telescope is usually called a drive clock; in modern telescopes it is often an electric motor controlled by a variable frequency generator. A telescope is usually driven, about its polar axis, at the sidereal rate so that one rotation is completed in 23h 56m 4s, the duration of one sidereal day. Small corrections are required in drive rates because of atmospheric refraction and when following the Moon or planets, which move relative to the stars. These corrections are achieved by varying the frequency supplied to the drive motor.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Equatorial Mounting


a telescope mounting that has two axes of rotation. One axis is directed toward the celestial pole and forms with the plane of the horizon an angle equal to the geographic latitude of the point of observation. The second axis is perpendicular to the first and lies in the plane of the celestial equator. The axes permit the telescope to be turned and directed at a point of the sky with specified coordinates (hour angle and declination). To compensate for the diurnal motion of the stars, the telescope is turned by a clock mechanism around the polar axis at a rate of one revolution per sidereal day.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

equatorial mounting

[‚e·kwə′tȯr·ē·əl ′mau̇nt·iŋ]
The mounting of an equatorial telescope; it has two perpendicular axes, the polar axis (parallel to the earth's axis) that turns on fixed bearings, and the declination axis, supported by the polar axis.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Caption: iOptron's new CEM120 Center-balanced Equatorial Mount is the company's current heavyweight, with a rated load capacity of up to 115 pounds.
The telescopes have a C-ring equatorial mount, with an optical design comprised of an f/2.5 Hextek light-weight primary mirror and a 330mm diameter Hextek secondary.
They deliberately designed the English cross-axis equatorial mount to be strong and stiff enough to carry the mass of a 60-inch reflector, should a larger telescope someday be desired.
The top of the tube was set at a height which would result in a height over the observatory floor of 80cm--I had to extend this by another 30cm when I moved from a fork to a German equatorial mount. Around the top and bottom of the pier I clamped shaped 50x150mm oak timbers and connected these with four vertical 50x75mm oak struts--these give a very solid 300mm square platform on which to install the mount.
The telescope has an open-lattice carbon-fibre truss-tube with light-weight Hextec mirrors on a split-ring horse-shoe equatorial mount. A prototype mount fitted with two smaller telescopes was installed in the test dome in their car park.
While in a pinch it could be mounted on a small tracker, the Meade performs best on a full-sized but small equatorial mount capable of accepting an autoguider.
The principal piece of equipment that every advancing astrophotographer needs is a good tracking equatorial mount. That's because the biggest hurdle we face is that our targets are constantly moving across the sky.
Joop de Jager presented his imposing black instrument on a foldable split-ring equatorial mount with electronic drive control.
To make the necessary star-trail image, you need to attach a digital camera with a standard or a short telephoto lens to your equatorial mount or telescope tube and direct it at the celestial pole.
My 30cm LX200 optical tube does not have a dovetail bar so the options for attaching it to a commercial German equatorial mount boiled down to three: screw a plate between mirror cell and corrector cell onto which a dovetail bar could be mounted; make a cradle to wrap around the tube and attach that to a dovetail; or, possibly, buy a commercial system like a Homeyer (4) or Parallax Instruments (5) cradle.
The German equatorial mount was manufactured by Software Bisque, located in Golden, Colorado, USA.