Editing Equatorial mount (section)

{{short description|Mounting system for camera or telescope}}
{{redirect|Polar axis|the mathematical concept|Spherical coordinate system}}
[[File:Forststernwarte Jena 50cm-Cassegrain 1.jpg|250 px|thumb|right|A large German equatorial mount on the Forststernwarte Jena 50cm [[Cassegrain reflector]] telescope.]]

An '''equatorial mount''' is a mount for instruments that compensates for [[Earth's rotation]] by having one [[rotational axis]], called ''polar axis'', parallel to the [[Earth's axis]] of rotation.<ref>{{cite web | url = http://www.astrogea.org/soldevilla/las_monturas.htm | title = LAS MONTURAS | publisher = Observatorio J. A. Soldevilla | access-date = 2008-09-20 | archive-url = https://web.archive.org/web/20180728224834/http://astrogea.org/soldevilla/las_monturas.htm | archive-date = 2018-07-28 | url-status = dead }}</ref><ref>{{cite web | url = http://www.oarval.org/LXD55PolAlign.htm | title = Observatorio ARVAL - Polar Alignment for Meade LXD55/75 Autostar telescopes | publisher = Observatorio ARVAL}}</ref> This type of mount is used for astronomical [[telescope mount|telescopes]] and [[camera]]s. The advantage of an equatorial mount lies in its ability to allow the instrument attached to it to stay fixed on any [[celestial object]] with [[diurnal motion]] by driving one axis at a constant speed. Such an arrangement is called a ''sidereal drive'' or ''[[clock drive]]''. Equatorial mounts achieve this by aligning their rotational axis with the Earth, a process known as ''[[polar alignment]]''. 
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[[File:Equatorial mount principle.svg|250 px|thumb|The green equatorially mounted telescope rotates at the same rate as the Earth but in the opposite direction, while the red telescope is not driven.]]
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[[File:Equatorial mount.svg|thumb|upright=1.5|Principle of operation and effect of an equatorial mount, assuming the subject is far enough that parallax is negligible]]