Private Eyes

We somehow doubt that Galileo Newton, Halley and other pioneers of modern astronomy had in mind the type of full moon that's pictured here when they squinted skyward questing further knowledge of heavenly bodies. But we do know that today's telescopes and spotting scopes are great fun--and if you should zero in on a planet or a constellation while trying to bring an object of somewhat different configuration into proper perspective, that's OK, too. Invented in (concluded on page 190)Private Eyes(continued from page 123) Europe during the 17th Century, the telescope immediately began to unlock the secrets of the heavens. Galileo's first telescope--a primitive instrument comprised of two lenses (convex and concave) separated by a tube--aided in destroying the popular philosophy that a stationary earth stood at the center of a revolving cosmos.

Although the telescopes pictured here probably aren't going to enable you to make any history-changing astronomical discoveries, they are great fun to gaze through. One peek and you'll find that that old devil moon is quite a ball of light; and when you finally tear your eyes away to zero in on one of the planets--by Jupiter!--the sight even beats reruns of Star Trek. (Jupiter, incidentally, is an especially good subject, as the planet's visual detail is exceptionally clear and its atmospheric features usually alter within the span of a night's viewing.)

You may wish to invest your money in a refractor telescope if you're just getting into stargazing. It uses one optical element--the objective lens--to focus light into a small image and a second lens (commonly known as the eyepiece) to magnify that image. Refractors come in all shapes and sizes; many offer zoom capability that will whisk you from, say, a wide, bright 20X (20 to 1 magnification power) to the detailed close-up of 45X. Models with 2.4- and three-inch apertures are readily available; biggies with four-inch apertures usually must be special-ordered from a manufacturer.

Reflector telescopes (often called Newtonians) are large tube-shaped instruments that have an eyepiece mounted near the aperture. They're ideal for a serious exploration of the night sky. Reflectors feature a primary objective mirror that receives light and reflects it to a smaller secondary mirror called a diagonal. This second mirror, tipped at a 45-degree angle, reflects the image produced by the primary mirror to an eyepiece that then magnifies it.

Reflectors call for a bit more maintenance than refractors, as the Newtonian's open-tube design allows dust and film to collect on optical surfaces that must, occasionally, be cleaned. Another very slight drawback is that the aluminum coating on the reflector's exposed mirror surfaces may deteriorate over the years, necessitating a recoating. The reflector, however, makes up for these slight inconveniences by providing the owner with a truly wondrous view of the heavens that's relatively inexpensive.

There's also a third, more complicated type of telescope on the market called a catadioptric, which essentially combines the features of both refractors and reflectors. In brief, catadioptrics amplify light rays entering the scope by an involved lens/mirror partnership. The result is an instrument that offers optimum viewing and exceptional compactness--one case in point being the Celestron 8 pictured here, which collects 510 times as much light as the unaided eye and permits magnifications ranging from 50X to 500X.

Now that you've got an idea of what types of telescopes you'll want to consider when making a purchase, let's take a closer look at their optical properties. First, there's something called light-gathering ability. This simply means that the more light that's gathered through an objective lens, the brighter the image you'll see. Light-gathering ability breaks down to the following easy-to-remember formula: Each time you double the diameter of the objective lens, you increase the light-gathering ability fourfold.

Resolving power is the ability of a telescope to separate heavenly bodies that are very close together. Poor resolving power may show two distant stars as a blob of light; an instrument with higher-quality resolve will separate them into distinct pin points.

Most telescopes--especially the imported ones--come with a skyful of impressive accessories, often neatly housed in a handsome wooden box that can be left out on display or stashed in a closet. And almost all models include a handy little 5X or 6X telescope called a finder that's permanently mounted on the side of the instrument. The purpose of the finder is just what the name implies; its wide field of vision helps you locate celestial objects much more easily than you could with the big scope.

Other accessories that may be included with your unit are: eyepieces for low, medium and high magnifications; a Barlow lens, which doubles or triples the magnification of each eyepiece; a star diagonal that will enable you to zero in on objects directly overhead; an erecting prism that rights the upside-down images refractor models originally produce; a sun screen and a moon filter.

There are also some truly nifty optional goodies on the market in the form of clock drives that rotate the telescope along its polar axis at the rate of one revolution per day. All the clock drives we know of use 110-volt A.C. power and allow for fine-motion adjustments by means of control knobs.

A word about spotting scopes: These and most inexpensive refractor models aren't powerful enough for sky watching, but they will provide amazing close-ups of the apartment just across the way.

By now, we hope you're as turned on to telescopes as we are--and if you spot any heavenly bodies that we might be interested in, be sure to let us know.

Turn to page 190 for detailed information on these scopes.