Tools of the Trade

Jack Kramer

When non-astronomers look through your telescope at a galaxy or nebula, chances are pretty good that they will be underwhelmed. Philosophically they may appreciate what you're showing them, but visually it's often not as awesome as they had expected. The difference is that you realize that the object will be faint. And here is where the experienced observer calls on some tools of the trade - the know-how that helps us coax minute details from that minute bit of light.

The phrase "tools of the trade" may conjure thoughts of telescopes and other astronomical hardware. But for a serious observer, the real tools are observing techniques themselves. When reading accounts of observations, you may have wondered how certain individuals are able to see so much detail in faint objects using relatively small telescopes. The answer is that they know how to look. Walter Scott Houston was one of the better known amateur astronomers and a prolific writer on deep sky observing. Reading some of his works, you might assume that he used a large telescope. Not so. A great percentage of his observations were with a 4-inch Alvan Clark refractor. It was a good instrument, but more importantly, he made the best possible use of it. Phil Harrington, author of the book Star Ware, noted that the ability to see fainter magnitudes depends largely on the experience of the observer. The 18th century astronomer William Herschel perhaps said it best: "Seeing is in some respects an art that must be learnt".

The most familiar tool is averted vision. Here the observer looks slightly to one side of where the object lies in the field of view. This takes advantage of the fact that our peripheral vision is somewhat more acute than when we look at an object straight on. When we stare directly at an object, the image falls at a point where the optic nerve enters the back of the eyeball, so there are fewer rods and cones at this spot.

While we're on the subject of eyesight, a relaxed observing eye is a better detector of faint detail. To prevent eyestrain, many observers learn to observe with both eyes open, rather than keeping the unused eye tightly shut. This also relaxes the facial muscles. Ron Wodaski, an amateur from Washington state, reflected on the strain inherent in one-eyed viewing: "If I relax my face muscles, the closed eye pops open and I cannot prevent it. I have to scrunch up my whole face pretty good to keep one eye open and one eye closed." On a recent trip to New Mexico, I discovered that there was a certain faint galaxy that I was able to see only with averted vision, but when I kept both eyes open I was able to see it directly. A helpful trick is to wear a convex-shaped eye patch over the unused eye. Yes, you'll look like a pirate, but who cares in the dark!

And speaking of the dark, one of the tools of the astronomer is the ability to select a good observing site. For deep sky observing, that means finding a site that is as dark as possible - something we've talked about many times in these pages. If you're pretty much homebound, then it becomes a matter of finding a spot in your backyard that is free of extraneous light.

It's also a good habit to record your impressions about what you see, or better yet, try to draw the object. This improves your powers of observation by forcing you to look for distinguishing characteristics so you'll have something to report about each object. A running joke is that a lot of observers record the identical comment about all deep sky objects: "faint and fuzzy"! But within that fuzziness may lie a wealth of detail, and looking for detail is how discoveries are made.

If you locate an object then quickly move on to something else, the chances are pretty good that you won't see many details. You have to look at an object for awhile. There are a couple of reasons for this. First of all, sky conditions are constantly changing, so you might catch that one moment when conditions are most conducive to seeing fine detail. This applies especially to solar system observing, since the planets often reveal a wealth of fine detail that is visible only in moments of especially good seeing. If you think you saw something, but don't see it again, the chances are pretty good that you did actually see it just long enough for it to register in your eye and brain.

Another reason for prolonged observation is that to a limited extent, it seems that our vision has a capability to become more acute with longer observation, in much the same way as film absorbs light during a long exposure. Several observers have commented on this phenomenon, so perhaps it's not just an illusion. At the very least, prolonged observation sort of "conditions" your eye to catch whatever is in the field of view. Or perhaps it's just your mind becoming more attentive.

Astronomical objects reveal themselves to us in subtleties. For example, slight gradations in the brightness of a galaxy are often referred to as "mottling", and may indicate that you've detected some of the spiral arm structure. The edges of objects are seldom sharply defined. That's because smaller telescopes are not able to detect the gradual thinning out of stars or gas at the extremities of galaxies or nebulae. But if you're able to see a more sharply defined edge, then that might indicate a dark absorption lane.Galaxies often have brighter hubs and/or central condensations. Do you notice a slightly brighter center of the galaxy? That means it's likely to be a spiral galaxy, since ellipticals tend to be more uniform in brightness across their surfaces. Planets, too, contain many low-contrast details. A better telescope or eyepiece provides more contrast between light and dark areas; it is this capability that let's us see more of the subtleties.

If you aspire to make the most of your time under the stars, then the tools of the trade - your powers of observation - will be more critical than the size or power of your telescope. These skills are acquired over time and nurtured with practice. It is often said that the best telescope is the one that is used most often, and in the same vein, the most skilled observer is the one who most often uses the "tools of the trade".