GoTo (telescopes)
Encyclopedia
In amateur astronomy
, "GoTo" refers to a type of telescope mount
and related software which can automatically point a telescope
to astronomical object
s that the user selects. Both axes of a GoTo mount are motor driven and are controlled by either a microprocessor
-based integrated controller or a personal computer
, as opposed to the single axis semi-automated tracking of a traditional clock drive
mount. This allows the user to command the mount to point the telescope to a right ascension
and declination
that the user inputs or have the mount itself point the telescope to objects in a pre-programmed data base including ones from the Messier catalogue, the New General Catalogue
, and even major solar system bodies (the Sun, Moon, and planets).
Like a standard equatorial mount
, equatorial GoTo mounts can track the night sky 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 alt-azimuth telescope mounts
.
and azimuth 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
. 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.
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.
Amateur astronomy
Amateur astronomy, also called backyard astronomy and stargazing, is a hobby whose participants enjoy watching the night sky , and the plethora of objects found in it, mainly with portable telescopes and binoculars...
, "GoTo" refers to a type of telescope mount
Telescope mount
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...
and related software which can automatically point a telescope
Optical telescope
An optical telescope is a telescope which is used to gather and focus light mainly from the visible part of the electromagnetic spectrum for directly viewing a magnified image for making a photograph, or collecting data through electronic image sensors....
to astronomical object
Astronomical object
Astronomical objects or celestial objects are naturally occurring physical entities, associations or structures that current science has demonstrated to exist in the observable universe. The term astronomical object is sometimes used interchangeably with astronomical body...
s that the user selects. Both axes of a GoTo mount are motor driven and are controlled by either a microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
-based integrated controller or a personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
, as opposed to the single axis semi-automated tracking of a traditional clock drive
Clock drive
In astronomy a Clock drive is a regulatory mechanism used to move an equatorial mounted telescope along one axis to keep the telescope in exact sync with the apparent motion of the celestial sky...
mount. This allows the user to command the mount to point the telescope to a right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
and declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
that the user inputs or have the mount itself point the telescope to objects in a pre-programmed data base including ones from the Messier catalogue, the New General Catalogue
New General Catalogue
The New General Catalogue of Nebulae and Clusters of Stars is a well-known catalogue of deep sky objects in astronomy. It contains 7,840 objects, known as the NGC objects...
, and even major solar system bodies (the Sun, Moon, and planets).
Like a standard equatorial mount
Equatorial mount
An equatorial mount is a mount for instruments that follows the rotation of the sky by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras...
, equatorial GoTo mounts can track the night sky 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 alt-azimuth telescope mounts
Altazimuth mount
An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two mutually perpendicular axes; one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth of the pointing direction of the instrument...
.
How a GoTo mount works
GoTo mounts are pre-aligned before use. When they are powered on, they may ask for the user's latitude, longitude, time, and date (they can get this data from a GPS receiver connected to the telescope, or even built into the telescope mount itself and the telescope mount controller can have a real time clock).Alt-azimuth mounts
Alt-azimuth Go To 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 altitudeAltitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
and azimuth 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
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
and declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
. 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.
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 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 CielCartes du CielCartes du Ciel is a free planetarium program for Linux, Mac OS X and Windows. With the change to version 3, Linux has been added as a target platform, licensing has changed from freeware to GPL and the project moved to a new website....
- CelestiaCelestiaCelestia is a 3D astronomy program created by Chris Laurel. The program is based on the Hipparcos Catalogue and allows users to travel through an extensive universe, modeled after reality, at any speed, in any direction and at any time in history...
- Hallo Northern Sky (HN Sky)HNSKYHNSKY or Hallo Northern Sky is a freeware planetarium program for Microsoft Windows to simulate the night sky. It is provided with several non-English language modules, as well as several stellar databases....
- KStarsKStarsKStars is a planetarium program using the KDE Platform for Unix-like computer operating systems. It provides an accurate graphical representation of the night sky, from any location on Earth, at any date and time...
- List of telescope parts and construction
- List of telescope types
- NASA World WindNASA World WindWorld Wind is an open-source virtual globe developed by NASA and the open source community for use on personal computers. Old versions need Microsoft Windows but the more recent Java version, , is cross platform and provides a suite of . The World Wind Java version was awarded in November 2009...
- Starry NightStarry Night (planetarium software)Starry Night is commercial planetarium software, available for Mac OS X, Microsoft Windows and for the iphone. Starry Night focuses heavily on providing attractive, realistic imagery, although recent versions have also increasingly targeted the amateur astronomy community with features like...
- Stellarium
- XEphemXEphemXEphem is a Motif based ephemeris and planetarium program for Unix-like operating systems developed by Elwood C. Downey.XEphem uses* The VSOP87D planetary theory for Solar System ephemeris,...