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The altazimuth type is the simplest as it involves only two axis, altitude and azimuth. Usually based on friction or some other adjustable means of keeping the telescope pointed in a certain direction. Perhaps the simplest variation of these is the infamous Dobsonian telescopes. These are usually home-built and use some pieces of Teflon to allow for smooth and stable positioning of the telescope. One set controls the direction vertically, along the altitude, the other set controls the horizontal movement or it‘s azimuth.
Other types of altazimuth mounts use turn-able knobs that can tighten a screw which causes the friction to secure, or to loosen the telescope. Some of the more sophisticated types also allow for ‘slow-motion’ controls, which can be turned to permit minor adjustments in the telescopes alignment. All of this is important when you want to look at a particular object in the sky.
Why? Because the Earth rotates. Any object in the sky will move at least one degree of arc across the sky every four minutes. In the cases of satellites, or the International Space Station, they move at an even faster rate across the sky. Meteors move the fastest.
So if your object of study some evening is Mars or the Andromeda galaxy, you’ll need to keep adjusting the direction of your telescope as these objects move across the sky based on the Earth’s rotation. Or, if all this adjusting seems too much work, you invest in a telescope with an equatorial mount. A mechanical device using weights as a counter balance to allow for smooth and accurate positioning.
The key advantage to an equatorial mount is that it uses a three-axis system to position a telescope. Star’s are usually mapped in the sky based on their ‘Right Ascension’ , their position on a longitude line, and their ‘Right Declination’ along a latitude line. With the equatorial mount, we also get a ‘Polar axis’, which positions the telescope on the basis of the Earth’s rotation by aligning the telescope with Polaris.
If you wanted to watch one particular object for a length of time, say long enough to take a photograph of it, then you only need one electric motor attached to the Polar axis to track the object once you had the other two axis ‘dialed in’. In your fully automated, computer-controlled telescopes, all the axis would be motorized.
Now, there are variations of everything these days. Some of the popular types of catadioptric telescopes use a ‘fork mount’ which is fully automated with computer controlled motors that are based on both the altazimuth and equatorial mounts. Again, these types are very easy to use. They come with a control device and usually with additional software for your home computer. You can literally plan out an observation schedule and program your telescope to execute it. On the other side of the coin, the Dobsonian is probably the simplest type of mount, and the cheapest. So if your budget is small and you want to buy the most ‘optics’, then this type is the best way to go.
But there is much to be said for the quaintness of the doing things yourself. So, when selecting your first telescope, the key factors to consider, along with price, are #1) What is your main interest? What do you want to see with it? #2) Where am I going to use it? How easy can I transport and set it up? #3) How well will it track an object in the sky? Well enough for photography? Once you establish these criteria, you then narrow your selection down to price. Keep in mind, that as with any hobby, there are always accessories, and that is what I will discuss next time.