…continuedSecrets of Deep-Sky Observing
Every deep-sky observer, even those with computer-pointed telescopes, will appreciate highly detailed star charts such as those in Uranometria 2000.0 or the Millennium Star Atlas. If you know exactly where a faint deep-sky object is supposed to be located in your telescopic field of view, you will be able to detect objects about a magnitude fainter than you could otherwise see with certainty. That's about like increasing your telescope's aperture by 60 percent. A 10-inch becomes a 16-inch.
Alternatively, a portable computer at the telescope can display the very detailed and flexible star-charting software available from many sources. Red cellophane over the screen will save your night vision.
When you pour all your concentration into examining a deep-sky object at the very limit of vision, does it get even harder to see after 10 or 15 seconds? Does the sky background brighten into a murky gray? Diagnosis: you're holding your breath without realizing it. Low oxygen kills night vision fast. An old variable-star observer's trick is to breathe heavily for 15 seconds or so before trying for the very dimmest targets. And keep breathing steadily while you're looking.
Night vision also is impaired by alcohol, nicotine, and low blood sugar, so don't drink, smoke, or go hungry while deep-sky observing. Bring a snack. A shortage of vitamin A impairs night vision, but if you've already got enough of it, taking more won't do any good. Few people in the developed world manage to get vitamin-A deficiency, unless they have a crappy diet of junk food, so don't expect a quart of carrot juice to improve your eyesight. But do eat your vegetables.
Prolonged exposure to bright sunlight reduces your ability to dark-adapt for a couple of days, so wear dark glasses when spending much time outdoors. Make sure the label on the dark glasses says they block ultraviolet light (both UVA and UVB); some cheap ones don't.
Over the years ultraviolet daylight (and maybe even bright visible daylight) ages both your eye lens and retina, reducing sensitivity and increasing the likelihood of degenerative diseases such as cataracts and macular degeneration. So if you wear ordinary eyeglasses outdoors, ask your optometrist to have an ultraviolet-filter coating applied to them. This option is so cheap and easy, and will reduce your lifetime UV exposure so greatly, that every eyeglass wearer ought to get it regardless of any immediate medical need.
Polycarbonate eyeglass lenses block ultraviolet light by themselves with no coating required, which lets you have antireflection coating applied to them instead highly recommended for any night-sky observer.
Most of all, be patient. If at first you don't see anything where a star cluster, nebula, or galaxy is supposed to be, keep looking. Then look some more. You'll be surprised at how much more of the scene glimmers into view with prolonged scrutiny another faint little star here and there, and just possibly the object of your desire. After you glimpse your quarry once or twice, you'll glimpse it more and more often. After a few minutes you may be able to see it almost continuously where at first you thought there was nothing but blank sky.
You can be confident that your observing skills will improve with practice. Pushing your vision to its limit is a talent that can only be learned with time. "You must not expect to see at sight," wrote the 18th-century observer William Herschel, often considered the founder of modern astronomy. "Seeing is in some respects an art which must be learned. Many a night have I been practicing to see, and it would be strange if one did not acquire a certain dexterity by such constant practice."