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How Telescopes Work


Telescope Mounts

The type of mount that you use will depend upon your observing needs. The two types are alt-azimuth and equatorial. Alt-azimuth mounts are simpler, easy to use, and cheaper than equatorial mounts. You set the horizontal and vertical coordinates of the object when sighting it, and then lock it in. You must readjust the horizontal and vertical coordinates as the object moves out of the field of view due to the Earth's rotation.

In contrast, equatorial mounts are more complicated, require some set-up, and are more expensive than alt-azimuth mounts. Equatorial mounts must be aligned with the Earth's poles. They often have counterweights to balance the weight of the telescope. Once the mount is aligned with the poles, you can set the coordinates of the target object (right ascension, declination). An equatorial mount will track an object's motion across the sky, and makes it easier to keep an object in the field of view. If you wish to do astrophotography, an equatorial mount is necessary.

Both mounts can come with slow motion controls, which help you make small movements of the mount to keep an object in the field of view (optional). Equatorial mounts may also have the following options:

  • setting circles - help you locate an object by dialing its coordinates (right ascension, declination)
  • motor drives - drive the motion of the telescope
  • computer interface - allow a laptop computer or personal digital assistant (PDA) to control the movement of the telescope

Regardless of the type of mount that you use, the most important thing is its stability. It should have a low center of mass and be able to support the weight of the telescope adequately. It should not vibrate when you touch it lightly. Finally, it should place the telescope at a comfortable height for you whether you decide to stand or sit.

Mounts can range in price from $150 to $2,000 depending upon the type and options.