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{{unreferenced, date=February 2014 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 ...
, "GoTo" refers to a type of telescope mount and related software that can automatically point 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 observ ...
at
astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often u ...
s that the user selects. Both axes of a GoTo mount are driven by a motor and controlled by a computer. It may be either a microprocessor-based integrated controller or an external personal computer. This differs from the single-axis semi-automated tracking of a traditional clock-drive equatorial mount. The user can command the mount to point the telescope to the celestial coordinates that the user inputs, or to objects in a pre-programmed database including ones from the
Messier catalogue The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ''Catalogue des Nébuleuses et des Amas d'Étoiles'' (''Catalogue of Nebulae and Star Clusters''). Because Messier was only in ...
, the New General Catalogue, and even major Solar System bodies (the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
, Moon, and planets). Like a standard equatorial mount, equatorial GoTo mounts can track the
night sky The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky include ...
by driving the right ascension axis. Since both axes are computer controlled, GoTo technology also allows telescope manufacturers to add equatorial tracking to mechanically simpler
altazimuth mount An altazimuth mount or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two perpendicular axes – one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth (compass bea ...
s.


How a GoTo mount works

GoTo mounts are ''pre-aligned'' before use. When it is powered on, it may ask for the user's latitude, longitude, time, and date. It can also get this data from a
GPS The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
receiver connected to the telescope or built into the telescope mount itself, and the mount controller can have its own real time clock.


Alt-azimuth mounts

Alt-azimuth GoTo mounts need to be aligned on a known "alignment star", which the user will centre in the eyepiece. From the inputted time and location and the star's
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 ...
and
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. Mathematicall ...
the telescope mount will know its orientation to the entire sky and can then find any object. For accuracy purposes, a second alignment star, as far away as possible from the first and if possible close to the object to be observed, may be used. This is because the mount might not be level with the ground; this will cause the telescope to accurately point to objects close to the initial alignment star, but less accurately for an object on the other side of the sky. An additional reason for using two alignment stars is that the time and location information entered by the user may not be accurate. For example, a one-degree inaccuracy in the latitude or a 4-minute inaccuracy in the time may result in the telescope pointing a degree away from the user's target. When the user selects an object from the mount's database, the object's altitude and azimuth will be computed from its right ascension and
declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...
. Then, the mount will move the telescope to that altitude and azimuth and track the object so it remains in the field of view despite Earth's rotation. Moving to the location is called ''slewing''. When
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 ...
is involved, a further motor has to be used to rotate the camera to match the field of view for long exposure photographs.


Equatorial mounts

For an equatorial GoTo telescope mount, the user must align the mount by hand with either the north celestial pole or the south celestial pole. Assuming the user is accurate in the alignment, the mount points the telescope to a bright star, asking the user to center it in the eyepiece. Since the star's correct right ascension and declination is already known, the distance from what the user considered to be the celestial pole and the actual pole can be roughly deduced. Using another alignment star can further improve the accuracy of the alignment. After alignment the telescope mount will then know its orientation with respect to the night sky, and can point to any right-ascension and declination coordinates. When the user selects an object to view, the mount's software looks up the object's right ascension and declination and slews (moves) to those coordinates. To track the object so that it stays in the eyepiece despite Earth's rotation, only the right-ascension axis is moved.


See also

*
Cartes du Ciel ''Cartes du Ciel'' ("CDC" and "SkyChart") is a free and open source planetarium software, planetarium program for Linux, macOS, and Microsoft Windows, Windows. With the change to version 3, Linux has been added as a target platform, Software lice ...
* Hallo Northern Sky (HN Sky) *
KStars KStars is a freely licensed planetarium program using the KDE Platform. It is available for Linux, BSD, macOS, and Microsoft Windows. A light version of KStars is available for Android devices. It provides an accurate graphical representation of ...
*
List of telescope parts and construction Hardware Accessories *Finderscope *Iron sight * Reflector (reflex) sight * Cheshire collimator: A simple tool to collimate a telescope Control *Clock drive * GoTo Mechanical construction *Mirror support cell * Serrurier truss * Silvering Mounts ...
* List of telescope types *
Starry Night ''The Starry Night'' ( nl, De sterrennacht) is an oil-on-canvas painting by the Dutch Post-Impressionist painter Vincent van Gogh. Painted in June 1889, it depicts the view from the east-facing window of his asylum room at Saint-Rémy-de-Proven ...
*
Stellarium A stellarium is a three-dimensional map of the stars, typically centered on Earth. They are common fixtures at planetarium A planetarium ( planetariums or ''planetaria'') is a theatre built primarily for presenting educational and entert ...
*
XEphem XEphem is a Motif based ephemeris and planetarium program for Unix-like operating systems developed by Elwood C. Downey. History XEphem started as a Unix and Motif conversion of the IBM PC-based '. It was initially released in December 1993 wit ...


External links


Aligning an equatorial-mounted GoTo telescope in the northern hemisphere
Telescopes Astronomy software