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.

Don't expect to see everything an astronomical object has to offer right away. The first look always shows less than comes out with continued scrutiny. This is true whether your subject is a dim galaxy that can hardly be told from the blackness of space, or a hairline feature on the blindingly bright Moon.

Seeing Through the "Seeing." One reason it takes time to see detail is the unsteadiness of the Earth's atmosphere. Celestial objects constantly shimmer and boil when viewed at high power, thanks to weak but ever-present heat waves in the air around and above us. The severity of this shimmering — called the atmospheric seeing — varies from night to night and often from minute to minute.

As you watch an object quiver and churn, unsuspected detail will flicker into view during quick moments of stability when the view sharpens up — only to fade out again before you know it. The skilled observer learns to remember these good moments and ignore the rest. The quality of the atmospheric seeing matters most when viewing bright objects at high power, but it influences the visibility of faint ones too.

The main reason it takes time to see detail, however, has to do not with the atmosphere but with the eye and mind. Wringing everything possible out of very distant views means learning new visual skills that involve active, concentrated effort. You'll discover that the eye's picture of a difficult object builds up rather slowly. First one detail is noticed and fixed, and you think there's nothing more to be seen. But after a few minutes another detail becomes evident, then another.

To convince yourself of this, look at a piece of sky with the naked eye and try to spot faint stars. Some will be visible right away; others take a few seconds to come out. When no more appear, most people would quit trying. But keep at it for a few minutes. Chances are some more will glimmer into view in places you would have sworn were blank. After a while you're seeing stars that are at least a half magnitude (37 percent) fainter than at first.

The planet Mars provides another classic example of this effect. For the beginner taking a first look with a small telescope, Mars ranks as the most disappointing object in the sky. It's just a tiny, featureless, orange fuzzball. The beginner steps aside to let an experienced Mars observer look in the eyepiece. Silence. "There's the north polar cap. . . . That big dark area in the south must be Mare Erythraeum. Okay, I've got Sinus Meridiani. . . . There's a cloud patch on the western limb. . . . "

The beginner looks again. Nothing but a fuzzball. Well, maybe there is a bit of brightness at the north edge crawling around in the poor seeing, and the fuzziness isn't a perfectly uniform orange, but these hardly seem like things worth noticing. Nevertheless, the next time the beginner looks he or she won't be quite a beginner, and the bright spot and dark area will come into view more readily.

Training Your Eye. An excellent way to train yourself to see better is to make sketches. These don't have to be works of art; the idea is just to record details in your notebook more directly than you can with words. Star fields require no artistic talent whatsoever, but by sketching a field that contains a faint asteroid or outer planet, you can identify the intruder be checking back in the next few days or weeks and seeing which starlike speck of light changes position.

For practice sketching planets, try drawing the Moon with the naked eye. If you have reasonably sharp or well-corrected vision, the Moon shows much more detail to the naked eye than any planet will in a telescope! Make a semicircle a couple of inches in diameter by tracing some round object and then draw the terminator exactly as you see it on the Moon. Carefully add the major dark areas with pencil shading, then look for finer markings. By now you'll be seeing much more detail on the Moon's face than you ever thought possible without optical aid.