A telescope wouldn’t be terribly useful without something to hold it steady. Telescope mounts come in two general types: altitude-azimuth (or altazimuth) and equatorial.
The simplest type of mount is the altazimuth version. It has two perpendicular axes of motion, vertical (altitude) and horizontal (azimuth). Standard camera tripods have altazimuth mounts.
Because they are easy to use and cost less than equatorial mounts, altazimuth mounts are ideal for smaller, inexpensive, beginner telescopes. They’re also the mount of choice for terrestrial observing with spotting scopes. Some altazimuth mounts are equipped with slow-motion controls, which allow fine adjustment of the telescope’s aim to help zero in on target objects.
The Dobsonian Mount
One new version of altazimuth mount used widely by amateur astronomers is called the Dobsonian mount. Invented by San Francisco telescope-maker John Dobson in the 1970s, this boxy mount is constructed of wood and sits low to the ground. Besides being inexpensive, Dobsonian mounts are inherently strong — capable of supporting giant Newtonian reflectors. Teflon and other low-friction materials used on the bearing surfaces allow very smooth adjustment of the telescope’s position.
The equatorial mount is the preferred type for astronomy. It also has two perpendicular axes, but they are called right ascension (RA, or polar) and declination (Dec). When the RA axis is aligned parallel with the Earth’s rotational axis, objects can be easily "tracked" as they drift across the sky (due to Earth’s rotation) by turning just one of the slow-motion controls (RA) instead of two, as is required with an altazimuth mount.
An equatorial mount offers other advantages as well. A motor drive can be coupled to the RA axis for automatic sky tracking-a terrific convenience. Also, with better equatorial mounts, astronomical objects can be located by their celestial coordinates (found in observing guides and star atlases) using the RA and Dec setting circles.