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An Altazimuth or alt-azimuth mount is a simple mount used for moving a telescope, camera, helostatic mirror, or solar panel along two perpendicular axes of motion, one vertical and one horizontal. The vertical movement is known as the altitude, while the horizontal motion is called the azimuth.
The biggest advantage of alt-azimuth mounts is their simplicity in both manufacture and use. They are often used for beginner telescopes, or for spotting scopes, but are still widely in use for more advanced instruments. In the latter case, advanced electronics and motors are sometimes attached to compensate for the restrictions of the mount's simplicity.
In astronomy, alt-azimuth mounts were, for a time, surpassed in popularity by the more complex equatorial mount. The latter is more naturally suited for tracking astronomical objects in the night sky as the Earth spins on its axis, since its polar alignment means that only one axis need be adjusted rather than the two of an alt-azimuth mount. Being able to track such objects reliably is particularly important for astrophotography, as well as more advanced amateur astronomy, both of which became more accessible when equatorial mounts became affordable.
In recent decades, alt-azimuth mounts have once again become very popular for astronomical telescopes:
- Telescopes built on the very popular Dobsonian design employ a variant of the alt-azimuth mount due to its ease of construction. Dobsonian style telescopes are optimized for visual astronomy, and the alt-azimuth mount is more suitable for this larger class of instrument since it doesn't add the unnecessary mass, complexity, and expense of an equatorial mount.
- Affordability of modern electronics has been a further motivation for a return to alt-azimuth mounted telescopes, with their increased simplicity for manufacture and practical use. In particular, 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 may be used to rotate the camera to match the field of view.
- For the largest telescopes, the mass and cost of an equatorial mount is prohibitive. The simple structure of an alt-azimuth mount is much better suited to such large heavy instruments.
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