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The Christmas shopping season is upon us, and a child’s fancy often turns to thoughts of telescopes. I’ve had several requests to expand on my comments about telescope buying and the accessories associated therewith, so here goes:

The sad truth is that most ‘scopes sold at this time of year are not suitable for viewing the heavens. More often than not, a child’s squeals of joy on Christmas day will turn to real tears of frustration in January.

First rule: Arm yourself with knowledge before you buy. Some manufacturers and salespeople make claims that don’t mean anything at all and are usually designed to confuse the unwary.

Thus, learn the technical characteristics and terms connected with telescopes, or you’ll end up with a piece of junk rusting quietly in your garage. Also, note that the poor kid probably doesn’t have the fine-motor skills or knowledge of the sky to find anything. Personally, I wouldn’t buy a telescope for anyone younger than 14 or so. Generally speaking, you’re up, parents. Prepare to do all the work yourself, at least at the beginning. That’s actually a blessing in disguise. Stargazing should be a family affair. There’s nothing in the world that binds people together more than a night under the stars.

I can’t tell you all you need to know in this column. That’s what telescope buying guides are for. Check out the one at telescope.com, for example.

That said, most of the buying guides are at commercial sites where they want to sell you a telescope at maximum profit. So let’s hit the high spots — the terms and warnings you’ll need so as not to get snookered by some telescope salesperson.

APERTURE is the measure of the light-gathering power of a telescope. The more light it gathers, the more you can see. Telescopes use mirrors or lenses to gather light from the stars and planets. Telescopes that use mirrors are called reflectors. Lens-based telescopes are called refractors. Aperture is usually expressed as the diameter of the mirror or lens that gathers the light. It should be at least six inches in diameter, or you won’t be able to see much.

Aperture is sometimes expressed in millimeters (mm) to confuse the issue. A 60mm refracting telescope sounds so much better than a 2.6-inch telescope, and such telescopes are, frankly, junk. The same can be said for most of the available 114mm (4.5-inch) reflectors.

MOUNTING. A telescope should be mounted on a sturdy platform, which must be beefy enough to keep the telescope pointed in the proper direction. The junk telescopes mentioned above are so wobbly that most people can’t keep them pointed.

A relatively inexpensive alternative is a six-inch reflector on a Dobsonian mount. Dobsonians use a sturdy wooden cradle to hold the telescope tube. They look more like siege cannons than telescopes, but they are remarkably stable.

COST. A usable 6-inch Dobsonian telescope will cost, at minimum, about $350 including the cost of the shipping. Spend any less on a smaller telescope, and you’re wasting your money. I know of no place in Central Ohio that sells quality telescopes, but I’d be glad to hear otherwise if somebody wants to tell me so.

If $350 is beyond your means, consider a pair of binoculars and a book on binocular observing. Buy the book first. It will provide advice on what kind of binoculars to buy.

ACCESSORIES. The eyepiece(s) provided with the telescope should be mounted in 1.25-inch-diameter barrels, not the smaller, cheaper variety.

The finderscope (or “finder”) is a small refracting telescope mounted on the side of the main ‘scope. An absolute necessity if you’re ever going to find astronomical objects, the finder should have an aperture of at least 30mm (1.18 inches). I prefer the 50mm version.

Also, don’t forget a good set of star maps. (See my Nov. 14, 2011 column for more-detailed advice on that score.)

MAGNIFICATION. Telescopes don’t work well at extremely high magnification. An astronomical telescope will only magnify well at 30 “power” per inch of aperture. A six-inch Dobsonian is rarely used above 180 power. Smaller telescopes that advertise obscenely high magnifications (“magnifies to 400 power!!!”) are stone-cold rip-offs.

APPEARANCE. The manufacturers of junk telescopes work hard to festoon their products with a lot of chrome knobs and doodads. A good, inexpensive telescope is large, stable, and rather plain looking.

HIGH PRESSURE SALESMANSHIP. Don’t listen to such claims as, “Better buy it now. They’re going fast.” They can always order you another one, and it’s far better to disappoint a child at Christmas than to turn her off permanently to the grandeur of the universe with a junk telescope.

Think three times before laying out any money. In fact, given all you’ll have to learn, by the time you read this, it’s probably too late. Start thinking now about next Christmas.

Above all, call me at 740-363-1257 before you buy. I really mean it. Think of it as a reward for making it all the way to the bottom of this column.

Tom Burns is director of Ohio Wesleyan University’s Perkins Observatory in Delaware. He can be reached at tlburns@owu.edu.

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