Amateur astronomy is about observing: Each and every time you look through an eyepiece, you make contact with a distant part of the universe. I’ve assembled this list of observing tips — one for each letter of the alphabet — to help you get the most out of those precious moments behind the eyepiece. I’ve discovered some of them on my own, but others were passed on to me by wise observing buddies. Read them, use them, and add to them. If you do, you’ll become a better observer.
AVOID EYE FATIGUE. Take short breaks, and try one of these simple eye exercises every 20 minutes or so. Lightly cup your eyes with your palms and relax for 60 seconds. Or simply look away from the eyepiece and roll your eyes up, down, around, and side to side for 20 seconds; then relax, eyes closed, for another 30 seconds.
BATTERIES. Take the batteries you know you’ll need — as well as the batteries you think you won’t need.
CAMERA FOCUSING. Astrophotographers want their lenses focused at infinity, but newer autofocus lenses can go past infinity when focused by hand. To resolve this problem, set the lens at infinity during the day and then lock it there with one or two wraps of tape around the barrel. Use tape that won’t leave a residue (no duct tape). Manual focus lenses don’t have this problem, but some astrophotographers tape them anyway. It’s one less thing that can go wrong.
DARK ADAPTION is the process by which the eyes increase their sensitivity to low levels of illumination. In the first 30 minutes, sensitivity increases 10,000-fold, with little gain after that. But brief exposure to bright light temporarily rolls back this hard-won increase. Just how much dark adaption you lose depends a little on the intensity and a lot on the duration of the light. A single flash from a strobe does less damage than a bright light lasting a second or more. At night, your eyes are most sensitive to red light, which means that for a given brightness, you’ll see more in light of this color. Use a red light, adjust its intensity to the lowest usable level, and then gaze only briefly at the illuminated object.
EYE PATCH. Wear an eye patch over your observing eye while setting up equipment. Put it on as long as possible before the start of your session, and you will be rewarded with a fully dark-adapted eye when you’re ready to begin observing. Move the patch to your non-observing eye when you look through the eyepiece. This lets you keep both eyes open, a technique that reduces eye fatigue. (Skeptical? Try reading this story with one eye closed for 60 seconds.) Before checking charts with a light, move the patch over your observing eye.
FOCUS each time you put your eye to the eyepiece and anytime you have a question about the sharpness of an image.
GOING DEEP. When you’re observing objects at the limit of vision or looking for small details in brighter ones, use a technique sometimes called “rocking the scope.” Gently tap the mount or the telescope tube. It really helps faint details pop out!
HIGH-ALTITUDE OBSERVING results in a degree of hypoxia, or low oxygen in body tissues, that significantly alters low-light color perception. Most people notice visual changes when they travel to altitudes approximately 2,000 feet (610 meters) higher than where they live, although those living at or near sea level may not begin to notice such effects until they reach an altitude of 4,000 feet (1.2 kilometers).
INTOXICATION. Don’t drink and drive the telescope if you’re looking to do some serious observing. Why? Alcohol impairs vision.
JUST IN CASE. Pack a “space blanket” with your equipment. Made from a metal-coated plastic film, it will trap body heat when wrapped around you, giving you an edge in all but the most severe weather conditions. It also shields against wind and rain, weighs just a few ounces, and only costs a few dollars. Often advertised as a “survival blanket,” that’s exactly what it may be for you.
KNOW YOUR EQUIPMENT. If you’ve added a new piece of equipment to your observing lineup, set it up at home first. Any problem revealed in the light will be one less you’ll have to deal with in the dark. As a second step, set up in your yard and observe as if you were at your remote dark-sky site. It’s surprising what a test run like this will teach you.
LIMITING MAGNITUDE. No better gauge of observing-site quality exists than a direct measurement of limiting visual magnitude, or LM. Most observers determine their site’s LM by identifying the faintest star they can see, usually near the zenith. Others use a method devised by meteor observers, who count the number of visible stars within predetermined asterisms.