If Earth did not move, an alt-azimuth mount would be all that any of us would ever need. But our planet does spin, and we must deal with it. The second type of mount is called the equatorial mount. It was designed to track the apparent motion of the stars. It does this by aligning one of its axes parallel to Earth's spin. Please note that there are two types of equatorial mounts — manual and motorized. If you have a choice, select the motorized version.Digital setting circles
Either alt-azimuth or equatorial mounts may be upgraded with a set of digital setting circles (DSCs), available from many astronomy vendors, for example, Lymax Astronomy
All commercial DSCs work on alt-azimuth and equatorial mounts. An electronic rotary encoder is placed on each axis, and a small processor performs the transformation from the altitude and azimuth of the mount to the right ascension and declination of the sky.
DSCs appeal to those observers who like to understand the concepts of astronomical coordinate systems but want the processor to do the actual pointing. To set up DSCs, you must center either two or three bright stars (depending on the system) in the field of view. Then, after you enter an object's designation, you simply move your telescope until the readouts for right ascension and declination are at zero.Go-to drives
A go-to system is essentially nothing more than a DSC combined with a dual-axis motor driver. As with DSCs, go-to drives require you to center one or two stars for alignment. Most go-to telescopes manufactured today have a large database of objects from which you can select.
Go-to drives have been paired with global positioning system (GPS) electronics and electronic compasses. The result is an almost hands-free setup. The Meade series of GPS telescopes with the Autostar controller is a good example. If you choose the alignment option "Automatic," the go-to drive first acquires the GPS satellite constellation (as it is called). This allows the drive to figure out the position (longitude, latitude, and elevation) of the telescope. Next, it finds north, then true north, which is offset from magnetic north. Then, it electronically figures out whether the mount is level and compensates in both tip and tilt. After that, the first of two stars is placed into the field of view. You are asked to center the star and press "enter." This is repeated with a second star. Both stars, by the way, are selected by the telescope's computer, which already knows whether or not they are above the horizon. That's it. After three button presses of the control paddle, you're ready to observe.Mount stability
We call our instruments "telescopes," but the phrase "optical tube assembly on a mount" also works. In fact, it points out that half of any "telescope" is the mount. Some would say the mount is the more important part. An unstable mount will render the finest telescope unable to deliver quality images. If the mount is undersized, wind — the bane of most large telescopes — will not be your only enemy. You will experience "bouncing" images even when you are focusing.
The test of a quality mount is sometimes given as the "damp-down factor." This is the time it takes an image to stabilize (for the vibrations to dampen) after the telescope is moved or refocused. Under no circumstances should the image take more than 5 seconds to damp down. Regarding wind, a spring Texas gale is going to move even the stoutest of mounts. A better test is how your mount responds to a slight breeze.
There is a trade-off to having the "best possible mount," which would be affixed to a permanent pier sunk into several cubic yards of concrete in an observatory. Most observers want (and need) their telescopes to be portable. An amateur astronomer lucky enough to own a 24-inch Starmaster reflector realizes the "quick-look" type of observing session is pretty much out of the question.