Once you've obtained an astronomical telescope, what can you expect of it?
Both less and more than many new owners realize.
One of the fun parts of being an amateur astronomer is showing off the heavens to others. The "oohs" and "aahs" as people get their first good look at the Moon or Saturn are a pleasant reward for the proud telescope owner. Naturally, you will have aimed the scope at the most spectacular object above the horizon. Sometimes there's a temptation to show people more typical objects — ghostly, barely visible apparitions with obscure catalog numbers — "to give them an idea of real astronomy." The reactions then are not so encouraging, even when viewers are told they're looking at a recently recovered comet or a galaxy 50 million light-years away.
The truth is, most of the thousands of objects visible in amateur instruments are not the least bit spectacular. Anyone who gets a telescope expecting dramatic visual thrills is in the wrong hobby.
The riches that astronomy offers are of a different sort. Visual observing outdoors in the dark usually means working to detect something that's extremely faint, tiny, hard to find, or all three. The more difficult the task, however, the greater the rewards of success. The excitement lies in finding and seeing, first-hand, remote marvels far beyond our planet — and in gaining skills and knowledge as an amateur scientist.
Too many people buy a telescope as if it were a TV, expecting it to show pictures all by itself. It's more like a piano, which gives back only as much value as the work you put into it. Learning to use a telescope well is a whole lot easier than learning a musical instrument, however. If you practice the techniques described here, you'll soon master the skies.
Know Your Equipment
Naturally, everyone first tries out a new telescope in the daytime. This is when to become familiar with its motions, pointing, focusing, different eyepieces, and magnifying powers, so you can then do everything in the dark. Here are some things you'll want to get straight in daylight before taking your telescope out under the night:
The Finder. Most telescopes have a finderscope attached to the side to help aim it. You need a finder because the main telescope has such a tiny field of view — that is, it shows such a tiny piece of sky — that you can't tell exactly where it's pointed just by looking. The higher the power of your main telescope, the smaller the field of view. For example, at 50 power you're looking at a magnified piece of sky about as small as your little fingernail covers when held at arm's length. Pretty tiny!
An 8× finderscope, by contrast, displays about as much sky as a golf ball covers at arm's length. This is big enough so you can aim at something you see with the naked eye and get it in the finderscope's view. Once it's there, you center it in the finder's crosshairs. That should be a precise enough aim for the object to appear in the view of the main telescope.
First things first: you'll need to adjust the finder's alignment screws so it gets aimed parallel to the main telescope. In daylight, point the main scope at something at least several hundred feet away using the lowest-power eyepiece. (But not the Sun! Never look through a telescope that might get aimed at the Sun or you could blind yourself.) A distant treetop is ideal. Center it in your view. Never mind if it appears upside down.
Now look in the finder. See the treetop? Is it centered in the crosshairs? Adjust the screws holding the finder until the crosshairs line up on the target. Now check back in the main telescope to make sure it hasn't moved. Then switch to a high-power eyepiece in the main telescope, and repeat the operation until the finder is locked in position with perfect aim.
And why, you ask, is the treetop upside down or oriented at some other weird angle? The answer is that this is an astronomical telescope, and after all, there's no up or down in space. So it doesn't matter how the field is oriented. Turning the image right-side up would require extra optical parts, adding to the instrument's expense and possibly degrading its performance. ("Image erecting" lenses are best used in terrestrial telescopes: those intended for looking at things on Earth in daytime, when there's no shortage of light.)
The Mount. As noted in the article "Choosing Your First Telescope", telescope mounts come in two basic types: equatorial and altazimuth.
An equatorial mount allows the telescope to swing only in the directions of celestial north-south and east-west. An altazimuth goes up-down (moving in altitude) and side to side (azimuth). The altazimuth mount has the virtue of simplicity. An equatorial mount is ultimately more helpful, but it takes some getting used to.
If you have an equatorial mount, find its polar axis (the rotating part that's closer to the telescope's base; it may have a setting circle showing right ascension). Outdoors, place the telescope so the polar axis points roughly to where you know Polaris, the North Star, will be located after dark. The telescope's motion around this axis now traces the paths taken by celestial bodies across the sky as the Earth turns.
Sweep the telescope around its polar axis from the eastern horizon across the sky to the west to visualize the paths the stars will follow over the course of a night. The mount's motions may seem awkward and unpredictable at first. But remember that no matter where the telescope is pointed, it will move only toward or away from Polaris (celestial north-south) and at right angles to this direction (celestial east-west). The orientation of these two directions varies in different parts of the sky, but with some practice swinging the telescope around in daytime you'll get used to them.
The Fine Art of Observing
The challenge of astronomy is that we must view most of the universe from extremely far away. When you're trying to see something well on Earth, your instinct is to move closer for a better look. But when it comes to stars and galaxies, we're stuck where we are. So, ever since the dawn of telescopic astronomy, the art of observing has been the art of using your eye to the utmost of its ability.
Looking with care. When looking through the telescope, focus and refocus with care. A good observer is always fiddling with the focus, trying to get it just a hair sharper. Many people find it best to keep both eyes open, since squinting strains the working eye. You can cover the "off" eye with one hand or with an inexpensive eye patch, available at drugstores.
-- Continued on Next Page
© 2005 Reprinted with permission from Sky Publishing Corp.
