At nearly $3 billion for the Chandra X-Ray Observatory, astronomy can be a dauntingly expensive pursuit. Fortunately, you don’t have to spend quite that much to get started. In fact, you don’t really have to spend anything. A lot of observation can be done with the naked eye, and many local communities have active amateur astronomers who would be happy to let you gaze at the heavens through their telescopes. Some veteran amateur astronomers even warn newcomers that they will be disappointed with a telescope unless they first obtain some star charts and guidebooks and make an effort to learn the major constellations, perceive differences in brightness, and learn to explain the phases of the moon. “Learn to use your eyes before you buy a telescope,” they say. There’s some real value in this advice. You need at least a little working knowledge of the sky before you can locate much of anything with a telescope. In addition, the type of telescope you buy will depend in part on the type of observing that you want to do, and you won’t know that until you have a little experience. So our first piece of advice is to be patient: Don’t run out to a sale at your local Mega-Lo-Mart and buy a telescope just yet.

Do I Really Need a Telescope?

Few experiences with the night sky are more instantly rewarding than your first look at the moon, a nebula, or a planet through a telescope. Saturn, in particular, can look almost too perfect. One of us taught students (while in graduate school) who refused to believe that the planet that they were looking at through the telescope was real.

This student insisted that Saturn was a sticker on the telescope lens. However, it is also true that such an experience can be singularly disappointing if that shiny new telescope you bought at the mall turns out to be a piece of wobbly, hard-to-use junk. If you are willing to invest in a good telescope (we’ll talk about the magnitude of the investment in just a moment), and if you are willing to invest the time to learn how to use it, a telescope can be a wonderful thing to have. But will you use it? If you are an urban dweller who never escapes the streetlights of the city and are hemmed in by tall buildings, you may be better advised to spend your money elsewhere. Then again, owning a sufficiently portable telescope gives you a good excuse to pack up every once in a while and head for the country, where the skies are darker and the seeing is better. You might consider an alternative to both the naked eye and the telescope: a good pair of binoculars.

For handheld viewing, 7× magnification is comfortable for most people. If you have steady hands, 10× may work well for you, and if you have the hands of a (successful) brain surgeon, even 12× may work. Remember, the greater the magnification, the harder it will be to hold the binoculars steady because objects will wobble farther in your ever smaller field of view. Magnification means less than you think when it comes to viewing stars. While pointing a telescope or binoculars at the night sky will make stars that are too faint to see with the naked eye visible, all stars are so incredibly far away (the closest beyond our sun, Alpha Centauri, is about four light-years away) that a given star at higher magnification will still be nothing more than a point of light.

Magnification is also largely wasted if what you look at is too dim to see well. Get binoculars with the largest aperture (the diameter of the objective, or main lens) you can afford. An aperture of 50 millimeters is a good choice. Couple this with a 7× magnification, and you have a 7 × 50 pair of binoculars—a good allaround choice for handheld viewing. If you want to successfully use binoculars with a magnification of more than 10× or 12×, you will need to mount them on a camera tripod equipped with a binocular adaptor clamp or a specially designed binocular tripod; otherwise, the sky will be a blur. Binoculars have the advantage of being very portable, and whole guidebooks have been written about observing the sky with them (for example, Exploring the Night Sky with Binoculars, by Patrick Moore [3rd ed., Cambridge University Press, 1996]).

However, at anywhere from $200 to $1,000 and more, binoculars with high quality optics are not cheap; if you’re thinking about buying a pair of big, expensive binoculars, there are other possibilities you may want to consider. The “field of view” is the piece of the sky you can see through your telescope or binoculars. You can easily determine the field of view of a telescope-eyepiece combination if you know the apparent field of the eyepiece (this will be listed with the specifications of the eyepiece) and the magnification. Let’s say you have a magnification of 10×. The field of view is equal to the field of your eyepiece divided by the magnification. If your eyepiece has an apparent field of 45 degrees (1/4 of the sky from horizon to horizon) with 10× magnification, your telescope will have a 4.5-degree field of view. If the magnification were 100× with the same apparent field of the eyepiece, the field of view would be 0.45 degrees. What should be clear is that as the magnification is increased, the field of view (or how much of the sky you see) decreases.