An Altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two mutually perpendicular axes; a vertical (altitude) axis, and a horizontal (azimuth) axis. They are generally used with telescopes, cameras, radio antennas, heliostatic mirrors, or solar panels.
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Telescope altazimuth mounts
When used with an astronomical telescope, the biggest advantage of an alt-azimuth mount is the simplicity of its mechanical design. The primary disadvantage is its inability to follow astronomical objects in the night sky as the Earth spins on its axis the way that an equatorial mount can. Equatorial mounts only need to be rotated about a single axis, at a constant rate, to follow the rotation of the night sky (diurnal motion). Altazimuth mounts need to be rotated about both axes, at variable rates, and they also impart a rotation to the field of view.[1] The design also does not allow for the use of mechanical setting circles to locate astronomical objects. The advent of microprocessor based, two-axis drive systems and digital setting circles have removed some of these shortcomings.
Current applications
Typical current applications of altazimuth mounts include:
- Research telescopes
- Mounts for very large telescopes. In the largest telescopes the mass and cost of an equatorial mount is prohibitive and they have been superseded by computer controlled Altazimuth mounts.[2] The simple structure of an alt-azimuth mount allows significant cost reductions, in spite of the additional cost associated with the more complex tracking and image-orienting mechanisms.[3] An altazimuth mount also reduces the cost in the dome structure covering the telescope since the limited orientations of the telescope means the structure can be more compact.[4]
- Amateur astronomical telescopes
- Beginner telescopes. Altazimuth mounts are cheap and simple to use.
- Dobsonian telescopes. John Dobson popularized a simplified altazimuth mount design for Newtonian reflectors because of its ease of construction; Dobson's innovation was to use non-machined parts for the mount that could be found in any hardware store such as plywood, formica, and plastic plumbing parts combined with modern materials such as nylon or teflon.
- "Goto telescopes". It has often proved more convenient to build a simple alt-azimuth mount and use a computer to manipulate both axes to track an object, than to build a more mechanically complex equatorial mount that employs only a single motor. When astrophotography is involved, a further motor has to be used to rotate the camera to match the field of view for long exposure photographs.
References
- ^ Mahra, H. S.; Karkera, B. N. (1985). "Field rotation with altazimuth mounting telescope". Bull. Astron. Soc. India 13: 88.
- ^ Pierre Léna, François Lebrun, François Mignard, Observational astrophysics, page 147
- ^ Dawe, J. A.; Watson, F. G. (1985). "Design for a large altazimuth Schmidt telescope". Occas. Rep. R. Obs., Edinb. 16: 15-18.
- ^ Siegfried Marx, Werner Pfau, Astrophotography with the Schmidt telescope, page 18
See also
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