Information about Good Telescope Mounts
To be effective, the telescope must be firmly mounted so that it doesn't wobble or vibrate. Remember that the best telescope in the world will not perform well without a good, stable mount. You must be able to make coarse and fine adjustments to keep an object in view. This is quite a trick as the earth is rotating under our feet at 15 degrees an hour. The stars appear to move overhead, but the earth's rotation is causing the apparent motion. There are two general categories of telescope mounts: the alt-azimuth and the equatorial types.
An Alt-Azimuth Mount is the simplest and typically least expensive mount. The telescope can be slewed left and right (azimuth), or up and down (altitude). The simplest of these is the Dobsonian ("Dob"). Aiming is accomplished by holding the front edge of the telescope and moving it to the desired spot in the sky. The Dob must be readjusted in azimuth and elevation every few minutes to keep the object in view. It is great for casual observing because it is easy to set up, does not require alignment, and is very stable.
The alt-azimuth mounts, until recently, could not be easily motorized to track stars. That has now changed. Using computer-controlled motors, several manufacturers are building alt-azimuth mounts that will track the sky.
An Equatorial Mount is designed to have one of its two axes pointed at the North Celestial Pole near Polaris. During set-up, the mount must be carefully aligned. The polar axis can be motorized to exactly compensate for the rotation of the earth. Objects will then stand still in the eyepiece, making it easier to study the objects or take photographs. The simplest mount is turned by hand via a "worm gear" drive. All of this machinery costs money, but the convenience is very appealing. The most common variations of the equatorial mount used by amateurs are the "Fork" mount and the "German Equatorial" mount.
The Fork mount is most often used for the short tube catadioptric telescopes. It supports the telescope between the two tines of the fork, with the fork pointed at the North Celestial Pole. These mounts are popular because they are very compact and are always motorized. They are somewhat subject to vibration because of the long fork tines but can be successfully used for visual observing and astrophotography.
The German Equatorial mount is often used to mount refractors because of their long tubes. It uses a counterweight to balance the tube, which is mounted to one side of the polar axis. Heavy duty versions of these mounts are some of the most stable available and are ideal for long duration studies or astrophotography. They also have "setting circles" for finding objects in the sky.
The Go-To Mount (or "Go-To" Telescope) is a recent development that is becoming increasingly popular. These mounts, or telescopes, can be either alt-azimuth or equatorial, and each has its own advantages. They are equipped with a small computer and a motor on each axis. Once aligned with two bright stars in the night sky, they can be commanded, using a small hand paddle, to slew to a galaxy or any other celestial object in their database. These are referred to as "GoTo" telescopes, since they can be told to "go to" an object. Knowledge of the constellations and "navigation" stars is still required in order to align the telescope properly. Some familiarity with "Messier" and "NGC" catalogues is helpful
©2005 Indiana Astronomical Society