If you've clicked your way to this article, I assume you are either interested in buying a telescope or are at least flirting with the idea. Your dilemma, however, is you don't know a lot about telescopes in general, particularly what makes one a quality instrument and another not worth hanging your hat on. Moreover, there appear to be a staggering number of models on the market at wildly different prices. How can you know if the telescope you might buy is worth the money you are forking over?

Before buying anything -- breathe in, breathe out and ask yourself five common-sense questions.

1) Why do you want to buy a telescope?

Do you want to provide a meaningful learning experience for a child, or do you want to test the waters to see if little Jimmy or Becky will follow through with their interest? Or is this the first step toward your own personal pursuit in astronomy? Do you envision sweeping up a panoply of galaxies and star clusters, discovering a comet or looking down into the craggy craters of the moon? Perhaps you just want to have a telescope on hand for the next lunar eclipse or bright comet, or to take with you on camping trips.

In short, if your purpose is event-driven or casual observing, shoot for a simple, lightweight, low-cost telescope with a wide field of view and good optics. Ditto if you're buying a telescope for a child whose interest might be ephemeral. You might even consider binoculars.

If your or the child's interest is unquestionably spirited and steadfast, then you will want a telescope that will nurture rather than limit a developing interest. In that case, lay out a few more bucks for a larger, more well equipped model that has, it should go without saying, good optics. You won't regret it.

2) How much do you want to spend?

The answer to this question usually cuts through the fog of indecision. Good beginners' telescopes run anywhere between $250 and $600. More money buys more bells and whistles, but not necessarily more enjoyment. If you spend a lot of money on a complex telescope you don't use very often, how much fun can that be? You want a telescope that you will use and, perhaps, grow into -- not one that limits you the moment you take it out of the box or that you later rue for having spent too much money.

3) What do you want to do with your telescope?

To be honest, it doesn't matter what you plan to do with your telescope, just as long as you want to look at celestial objects with it. If you simply want a telescope that "looks good," I suggest you purchase one of those antique brass remakes sold in tony furniture shops. Their optical quality is terrible, but they look smashing when posed beside an ornamental birdcage or an early 20th-century French lithograph.

Seriously, whatever you want to observe -- planets, stars or galaxies -- you need to consider the diameter of the telescope's main light-gathering lens or mirror, called the objective. We'll explore this in more detail in the next section, but for now, suffice it to say that a telescope's "power" is squarely vested in its aperture, not its magnification capability. Telescopes are often described as "light buckets." The larger the light bucket's aperture, the more light it gathers; the more light it gathers, the more detail you can see, no matter what you're looking at. Hence, always buy as much aperture as you can afford. Like real estate, the more you have the greater your return.

4) How dark are your skies?

In other words, where will you be observing the most: from the city, suburbs or country? If you are fortunate enough to live away from city lights then put as much money as you can into aperture. Costly accessories -- high-dollar eyepieces, a computerized drive system and an electric focuser -- can wait. Get out there and observe.

5) How serious are you about astronomy?

A difficult question to answer but give it a try. Can you recognize some of the major constellations and brighter stars? Do you know where the planets are in tonight's sky? Do you keep up with the latest astronomy discoveries? If a moderately bright comet could be seen in the predawn sky, would you drag yourself out of bed to see it? Do you own more than one astronomy book or software program, or subscribe to a popular astronomy magazine like Sky & Telescope? Is your wall plastered with astronomical art or photos? Do you have two or three or more internet bookmarks that take you to astronomy-related websites?

I'm no psychologist, but it stands to reason that the more affirmative your answers are to these questions the more active your interest. That doesn't mean a telescope will necessarily enhance your enjoyment. Indeed, many people, myself included, enjoy scanning the night sky with the unaided eye and binoculars. But I suspect if you had the right telescope at your disposal, you'd probably get a lot of pleasure out of it. How much, of course, depends on you and how involved you want to become.

As you probably already know, there are all kinds of telescopes out there. In the next section, I'll cover basic telescope design, describe the various types of instruments available, and lay out their advantages and disadvantages. If you really want to buy a telescope that you won't later regret, press on to a quick lesson on light-gathering.