November 13, 2011
Up at Perkins Observatory, we get an enormous number of calls this time of year about buying telescopes. The best advice I can give is, “Don’t rush into a purchase.” You’ll find a lot of junk telescopes out there, and you need to make a thoughtful decision about what you put under the tree.
Instead, find a reputable telescope buying guide online, and arm yourself with knowledge. You’ll find a good one, if you don’t mind a commercial website, at telescope.com.
That said, let me answer the most common question: “What about the telescope I saw at the X Department Store or Y Camera Shop? It only costs $169.95.”
Please don’t. It’s probably too small. It’s probably too unstable.
Here’s the bottom line, expressed in the language of the telescope geek: The beginning telescope buyer should purchase a reflecting telescope with a six-inch diameter or larger mirror on a Dobsonian mount and not a smaller reflector or refractor, which is what you’ll find at most local stores.
See what I mean? You’ll need to know the language or the salesperson will start licking his or her chops.
“Reflectors” use mirrors to gather the light from the stars. The Dobsonian mount is a simple but stable wooden mounting for the telescope. It will not follow the stars across the sky, but it is sturdy and inexpensive.
A refractor uses a lens at the top of the telescope to gather the light. The refractors or small reflectors you’ll see at most local stores have three serious flaws.
First, to get good views, you’ll need a telescope with a light-gathering mirror or lens at least six inches in diameter. The smaller refractors found in many local stores are too small to see anything more than the craters on the moon and a few bright planets. You’ll get terrible views of everything else — star clusters, galaxies, and gaseous nebulae.
Second, a refractor with a six-inch lens requires a mount so large as to make its transportation to a dark-sky observing site difficult. The small telescopes sold at big-box and “science” stores have mounts so wobbly that you’ll have difficulty pointing the telescope and keeping it pointed once you find something. A reflector on a Dobsonian mount fits on the back seat of a small car. It points where you want it to point and stays there, eliminating the frustration of an unstable mounting.
Third, a six-inch refractor can set you back thousands of dollars. A six-inch reflector can be purchased online at telescope.com for about $325, including shipping. It’s all the telescope many people will ever need.
A good telescope will last a lifetime and can easily be resold if you lose interest. Don’t buy a cheap refractor or a reflector with less than a six-inch mirror just to save money. You will certainly lose interest because of its very limited range and difficulty of use.
If you can’t afford a decent ‘scope, consider binoculars as an alternative. A pair suitable for astronomy should have lenses at least 50 millimeters in diameter. (That’s the way binocular size is expressed. See what I mean about the complexities here?)
Avoid so-called “fixed-focus” binoculars. They are designed for looking at nearby objects on Earth. And for heaven’s sake, get binos with glass, not plastic, lenses.
Use binoculars to learn the sky while you save up for your eventual telescope purchase. You’ll be surprised at how much you can see, especially if you’re willing to travel away from light-polluted urban skies to a rural observing location.
Whatever instrument you choose, don’t forget to purchase a detailed set of star maps. Your telescope is useless if you can’t find anything in it.
Any well-stocked bookstore should have books that identify the locations of the best astronomical objects. You’ll also find specialized books just for binocular observing, but you might have to order them online.
Despite the relatively high cost, buying the telescope is the easy part. Learning to find your way around the nighttime sky is a lifetime labor of love. But once you embark on this great adventure, the universe and all the wonders in it will be at your command.
Tom Burns is director of Ohio Wesleyan University’s Perkins Observatory in Delaware. He can be reached at firstname.lastname@example.org.