A telescope can be the most expensive piece of metal and glass that sits on your shelf, or it can be your family's favorite toy. It all depends on how appropriate your decisions are when buying a telescope.
First, telescopes are not mere tubes with lenses at either end. Even the simplest ones are complex and relatively fragile, so they are not something to purchase until your children are mature enough to handle them with care.
Refracting telescopes are the simplest version. These scopes use precision-ground lenses at both the viewing end and the objective end (that's the big end), and also may use Barlow lenses and a mirror to increase the light-gathering quality of your telescope. The best refracting telescopes may have up to eight lenses throughout their construction. Overall, refracting telescopes have low maintenance and are excellent for clear viewing of planets and detail viewing. Look for the ones that have achromatic or apochromatic lenses. Apochromatics are better, but they are also significantly more expensive, sometimes by a factor of 10x the cost.
Reflecting telescopes are the ones that have much fatter barrels. That's because they depend on a well-cut mirror to collect light, rather than perfected achromatic or apochromatic lenses. While reflecting telescopes do a good job of gathering light so you can more easily view distant objects, they aren't as good as a quality refracting telescope for seeing small details on closer objects. For instance, the craters of the moon may not look as clear in reflecting telescopes, though you can see all the stars that make up the Pleiades without any problem. Newtonian reflectors have some of the detail problem corrected, but they still aren't perfect. And while refracting scopes need little maintenance, a reflecting telescope needs mirrors recoated every few years or it loses much of its light-gathering advantage. You may see high-end telescopes of this type marketed as Schmidt-Cassegrain.
There are a few other types of telescopes: the Ritchey-Chretien, which is a modified reflecting telescope; catadioptric telescopes, or compound scopes with elements of both refracting and reflecting types; and Schmidt camera telescope, a catadioptric scope designed specifically for photography. Because of price, most people opt for simpler refracting or reflecting telescopes for at least the first time out.
Selecting your telescope is not all you need to do; you must also select the proper mount, or tripod. The simplest is an alt-azimuth mount, which lets you move your scope up and down and left and right. More expensive are the equatorial mounts, which use alt-azimuth motion but also align themselves according to the earth's spin to make it easier to track heavenly bodies. The best mounts are the motorized equatorial mounts, which can be programmed to not just align themselves properly but even to find specific star bodies for you.
Next, look at magnifying power. This is not as important as you might think. Most telescopes come with eyepieces that provide higher magnification power. Don't pay attention to what the box says; instead, multiply the size in inches of the lens (on refracting) or mirror (on reflecting) of the scope by 50 to find out what the maximum useful magnification is, and depend on swapping out eyepieces to get your real magnification power. Lower magnifications are typically used much more than higher ones.
Larger telescopes in general, are better for viewing, but they are also more delicate. If you have a place where you're going to set up a permanent viewing station, it's worth it to get a large scope, but if you want high mobility, you should get a smaller good-quality scope.
If you live in a high-humidity area or a place where there are extremes of heat or cold in which you will be using your telescope, do not try to get away with a cheap telescope. Telescopes are very sensitive to both moisture and temperature, and your scope must be properly sealed to manage these extremes.
Finally, before buying a telescope, try to join a local astronomy club and check a few of the good ones out. Trying before you buy is always the best way to go, and you'll pick up lots of great tips from other club members in the process.
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