A Telescope's Other Half

Just as a car's engine is useless without a chassis and wheels, the optical tube assembly is only half a telescope. The other half is the mount. It is just as important as the optics if not more so. It has to be steady, sturdy, and smoothly working.

Telescope mounts come in two basic kinds. An equatorial mount allows the telescope to move in the directions of celestial north-south and east-west. This can be a big help. If you align one axis of an equatorial mount on Polaris, you can track celestial targets as the Earth turns by moving the telescope around just this one axis. Many equatorial mounts come with an electric motor to do this for you. Motor tracking is especially useful for high-magnification viewing and for showing celestial objects to groups of people. It's also a prerequisite for most through-the-telescope photography.

An altazimuth (altitude-azimuth) mount, by contrast, moves up-down (in altitude) and right-left (azimuth). A photo tripod is an example of an altazimuth mount. Another is the popular Dobsonian mount, shown below.

Altazimuth mounts are generally lighter than equatorials, in part because they don't require counterweights to balance the telescope. (I hasten to note, however, that the equatorial "fork" mounts sold with many compound telescopes are relatively lightweight, too; the photo above shows one example.) Dobsonian mounts, in particular, can be very stable and low-cost.

But altazimuths do not readily lend themselves to motorized operation, and you have to move the telescope in two directions simultaneously to track celestial objects as the Earth turns. While this becomes second nature to many observers, others find it maddening. (See the section below on "smart" telescopesfor a high-tech way around this problem.)

Your own personality should play a part in choosing a mount. Are you comfortable with instruments that require tools and a head for numbers to set up and use? Or are you looking for the astronomical equivalent of a point-and-shoot camera? A Dobsonian can be set up in the time it took to read this paragraph. An equatorial mount can take a bit longer if you want to get the most out of its features. Computerized "smart scopes," which promise easy object-finding, are actually the most complicated to deploy.