Astronomy is conducted in the dark. No surprise there. But some activities, like observing a galaxy or a nebula, require special attention to the red-flashlight technique. There is a difference between a red flashlight bright enough to find your way to the restroom and one that maintains your dark adaptation for chart reading and critical observing. In each case, use the minimum amount of red light necessary to do the job. The best red lights are adjustable in brightness, such as the one shown below with a thumbwheel dimmer. I consider a red light essential for backyard astronomy. You can order one by phone from any telescope shop in the country. Get one. Here’s why:
Redder and Dimmer
The human retina reaches the first stage of dark adaptation fairly rapidly, in about 30 minutes. Thereafter, over a period of hours, the eye makes incremental gains in its ability to detect faint objects. Unnecessary exposure to a bright red light — let alone white light — means that optimum levels of dark adaptation will never be attained. Even when using dim red light (to which the rod cells in the retina are least sensitive), experienced observers routinely close their observing eye when consulting charts, to ensure the best views of faint telescopic objects.
Not only are red flashlights often too bright for optimum observing, but they are frequently not red enough. Bulbs, LEDs and lenses that are already red can be painted with dark red nail polish to make them dimmer and redder. Alternatively, flashlight lenses and computer screens can be covered with Rubylith red masking film. Because the eye’s rod cells are not very sensitive to wavelengths of light longer than about 620 nanometres, the rule of thumb is: the redder the better.
Focus and Averted Vision
Having worked hard to reach an optimal level of dark adaptation, the best way to see even more detail in faint objects is simple: Don’t look directly at them. Instead, let your eye wander around the field of view, but pay attention to the object you are viewing — a technique known as averted vision. This counterintuitive trick often reveals much more detail for the simple reason that averting your gaze from the object places it on your eye’s night-sensitive rod cells, which are much more concentrated toward the periphery of your visual field.
When observing faint objects, focus first on adjacent stars. It is almost impossible to obtain accurate focus on a diffuse object such as a comet or a galaxy. Use the same trick for planets, because atmospheric seeing often makes accurate planetary focus difficult to attain — concentrate repeatedly and check focus on Jupiter’s moons, for example.
The best way to focus a telescope is to rack the eyepiece inward, not outward. Stop when the object appears sharp. Using the opposite approach allows the eye to accommodate as the focus changes, and the net result is a blurring of the object once the eye relaxes. A simple trick to reset the eye is to glance upward first — to objects located at infinity— and then focus the telescope while consciously keeping the eye relaxed.
Aside from maintaining your dark adaptation and employing averted vision, there are several things you can do when trying to detect faint, fuzzy objects in your telescope. First, once you have found an object, try using medium to high power (equal to 15 to 30 times the telescope’s aperture in inches). This darkens the sky and often makes objects at the threshold of detection stand out better. Second, try jiggling or gently tapping the telescope or sweeping it back and forth a bit. This often provides the additional sky contrast needed to glimpse a faint comet or galaxy.
Monk’s Hood and “Too Much” Telescope
When observing from a light-polluted backyard or an apartment balcony, consider draping a few yards of black felt or velvet over your head and shoulders as a light shroud. This so-called monk’s hood is extremely effective for attaining higher levels of dark adaptation, particularly when coupled with an electric dew heater to prevent the eyepiece of the telescope from fogging.
Sometimes glare from distant lights can’t be avoided, but if possible, prevent direct glare into your backyard by placing basketball-style poles and backboards to selectively block the offending lights.
Avoid buying too much telescope. Large telescopes are much less expensive than they were a generation ago. But the euphoria surrounding a big-scope purchase quickly wears off once you realize how big and heavy it is. Inevitably, a big, bulky scope that has to be transported even a short distance will be used less and less as time goes by. An 8-inch reflector or Schmidt-Cassegrain is sufficiently large to qualify as a “telescope for life.” It is small enough to be easily transported and large enough to provide a lifetime of fascinating observations.
Simple Photo Tracker and More
If you own a digital SLR camera, consider building a barn-door tracker for short, guided exposures of the night sky. Modern SLR cameras are extremely sensitive to low light (sorry, common point-and-shoot cameras are not), and exposures do not have to be very long. The barn-door tracker is easy to construct using everyday tools. Complete instructions for building a barn-door tracker are available on-line and in the guidebook NightWatch.
A simple way to delay the formation of dew on a small telescope or a finderscope is to construct a dew shield from an old corrugated cardboard box. Cut out the side of the box, and tear off the outer layer of paper on one side. Then roll the cardboard into a tube, placing the exposed corrugations on the inside. The dew shield can be covered with duct tape to waterproof the outside and sprayed with Krylon ultraflat black on the inside to eliminate reflections. A dew shield about four times longer than the diameter of the objective lens works very well.
You can’t buy your way into astronomy; it has a steeper learning curve than many hobbies, but aficionados will tell you it’s worth it for the mind-stretching benefits alone. If you are a beginner, be persistent. Go outside and observe every chance you get, and become familiar with the constellations and brighter deep-sky objects. You will gradually gain an appreciation of the ever-changing positions of the Moon and the planets and of the seasonal change in the constellations. Soon, you will realize that what was once a beautiful but unknown starry sky has become a celestial road map in your mind.
After purchasing their first telescope, most amateur astronomers realize that their long-forgotten binoculars are actually small, portable, handheld telescopes! Binoculars, with their generous wide panoramas, offer unique views of many deep-sky objects, such as the Pleiades and Hyades. Far from being occasional accessories, your binoculars should be observing partners with your telescope.
It is tempting to acquire a set of expensive eyepieces to cover every conceivable observing situation. In practice, though, a low-, medium- and moderately high-power eyepiece, plus a 2x Barlow lens, will meet almost all your observing needs.
When choosing a new eyepiece, keep the size of the exit pupil in mind. A dark-adapted eye can open only so wide. If you’re closer to 20 years old, don’t exceed a seven-millimetre exit pupil. If you’re over 40, don’t exceed five millimetres. Using an exit pupil larger than necessary effectively reduces the aperture of your telescope. To determine the exit pupil of a potential eyepiece purchase, divide the focal length of the eyepiece by the focal ratio of your telescope.
In guidebooks and in telescope advertising, a telescope’s maximum magnification is given as 50 power (50×) per inch of telescope aperture. This is mostly a theoretical concept, although it can be useful for star testing or splitting close double stars. Powers of around 25× per inch of telescope aperture are more reasonable for “high-power” planetary viewing.
Let your telescope cool after initial setup, especially for critical planetary observing. Most Newtonian and Schmidt-Cassegrain telescopes retain a great deal of heat when taken outside into the cool night air. Internal heat creates thermal plumes inside the telescope, disturbing the higher-power views. Depending on the size of a telescope, it may have to stand for a few hours before reaching equilibrium. Observe nonplanetary objects as your telescope cools. Alternatively, place a fan on a stool and let it blow directly onto the back of your Newtonian mirror. With a Schmidt-Cassegrain telescope, point it downward, remove the plug at the back and let it stand that way for an hour or two to let the heat escape.
In a similar vein, don’t try to observe through a window. The glass in a window is not optical glass, and the difference in temperature between the outside and the inside will make a clear view almost impossible.
Deal with dew by using a long extension cord and an electric hair dryer to warm up telescope optics. If you are out at a dark-sky observing site, use your car’s heater to warm up eyepieces or place a fogged eyepiece in a clean pocket so that body heat can warm it up.
In cold weather, thin polyester/Lycra gloves are extremely useful when setting up telescopes and handling eyepieces and charts while observing. These gloves have embedded rubber on the palms and fingers to ensure a positive hold when picking up delicate objects. Warm fleece mittens can be worn over the gloves when your hands get too cold.
Improving Your Skills
If you own a large telescope, particularly one that lives in a backyard observatory, an easily portable grab-and-go telescope is a way to cover all your observing situations, such as a brief sojourn to a dark site to see a horizon-hugging comet.
Sit down to observe, if you can. An observing chair or stool allows you to breathe deeply and really concentrate on what you’re trying to see. A fully oxygenated eye can detect fainter objects — or more planetary detail. Stay relaxed by keeping your nonobserving eye open. You can cup your hand over that eye to block out the stray light or try using an eye patch.
As you become more proficient at finding celestial targets, consider sketching objects that you see; this forces you to look harder at the object you are observing. There is a big difference between a quick look and an accurate sketch of what you saw.
Keep an observing logbook. It doesn’t have to be complex. Note the date, the time you spent observing and a list of the objects you saw. Note any interesting details. A logbook is a fabulous way to keep track of your progress in observing and a great way to remember unique events, because it serves as a personal diary of your time spent as a backyard astronomer.
While an equatorial mount is fine for imaging or high-power planetary observing, don’t dismiss a telescope with a simple altazimuth mount for visual observing. It will force you to star-hop and learn the sky and is lighter and easier to use.
If you own a large, heavy, solid-tube Newtonian telescope, consider installing handles or creating a sling to make it easier to carry out to the backyard. Even better, most backyard astronomers find they get outside much more often when they have a shed in which to store their telescope. Finally, think about purchasing one of the simple observatories now available. Few people regret having all their equipment set up and ready to go.
Dr. Dale Armstrong is a longtime amateur astronomer living in London, Ontario. One of his first recorded astronomical observations — made in 1973, when he was 11 — was a sketch he did of Jupiter while observing with a 40mm refractor.