By Chris Fellows, Serenity Mobile Observatory
This week I am going to take a break from the learning the night sky series and talk a little about some observing tricks that will help you pick out more detail in faint objects. If you have been following along you will remember that in “Let the stars be your road map – Part 2” I talked about setting expectations for what you will see at the eyepiece. Basically distant and faint objects appear as gray fuzzballs or smears in all but the largest telescopes under the darkest skies. This week I am going to teach you a few tricks that should improve your ability to see those “faint fuzzes” and enhance your celestial views.
The three most important things in astro-observing are location, location and location. Dark skies, away from city lights, is the single largest factor in your ability to pick out faint objects. Street lights, car headlights, yard lighting, the moon, and some friendly dude walking up with a flashlight will all adversely affect your ability to see. This happens both directly by scattering the photons in the atmosphere, graying what should be a velvety black sky, and indirectly by damaging your night vision adaptation. Get in your car or RV and get away from those lights. If you can’t do that, get behind your garage or a stand of trees that will block at least some of the light pollution. You will be surprised at how much even a slight reduction in light pollution will help.
That leads us to a second important factor: dark adaptation. The human eye is easily over-saturated by light. Once the receptors in your retina get saturated it takes up to 1/2 hour before your eyes are truly adjusted to the dark. This makes a huge difference in what you are able to see at night. This is very easy to prove to yourself. Sit out in the dark for a half hour and look up at the sky, make a mental note of the stars you can see. Now, quickly walk through a well-lit room and go back out. I am willing to bet that you won’t be able to pick out even half of the stars you could see before. So plan to observe, go out into the dark well ahead of attempting any observations and make sure to keep any full spectrum light out of your eyes. The modern culprit is the cell phone – leave it in your pocket.
Next let’s talk about drugs. Caffeine, nicotine, alcohol, amphetamines, antihistamines and cocaine are all drugs that can trigger vasoconstriction. Vasoconstriction is just what is sounds like – the narrowing or constricting of the blood vessels. When your vessels are constricted you get decreased blood flow and less oxygen to the tissues that need it to function properly. This includes the vessels that supply blood to the retina, degrading your vision. Stay off the drugs when planning a night under the stars. Conversely, you can increase your vision by simply breathing deeply. When at the eyepiece be mindful of your breathing – take slow and deep breaths. This will help you relax and increase your ability to pick out faint details and spot objects you would normally miss.
Jiggle your binoculars or telescope! The human brain has evolved to see motion. This helped us survive when that tiger was stalking us from the tall grass and pounced from the side. The quick movement is programmed in your brain to be noticeable. A tap on the side of your telescope will jiggle the view and faint objects will jump out at you.
Averted vision [Editor: Short, interesting article.] is my favorite trick in the observing bag. Its affects are active, meaning it is something you can purposely do in real time, and it has dramatic effect on your night vision. Simply speaking, you need to look slightly away from the object you are trying to see. I know that sounds weird but trust me, once you learn how to do this you will do it all the time. I use averted vision every time I look through the eyepiece. This needs a little explanation so let’s talk a little about the physiology of the human eye.
Our eyes allow light (photons) in through the opening called the pupil and through the lens which focuses it on the retina – specifically the area of the retina called the fovea where sharp color vision takes place. The retina contains special nerve cells that are sensitive to the photons and convert them into electrical signals that are sent down the optic nerve and interpreted by the brain as images. These special nerve cells come in two types, called rods and cones. There is a smallish indented area at the rear of the eye called the fovea. The fovea contains nearly all of the cone cells, about 6 million of them, which see color and has the sharpest focus.
The rest of the retina is made up of mostly rod cells, which are color blind but see contrast and luminosity. There are about 120 million rod cells in the human eye, or about 20 times the number of cone cells. These cells are spread over the rest of the retina. So, by looking slightly away from an astronomical object most of its light is moved away from the fovea and on to the parts of the retina where the rod cells dominate. Since there are so many more rods, and they are more sensitive to contrast, dim objects pop out where you couldn’t even see them when the light was directed on the fovea. I have attempted to depict this in the illustration showing the difference in what you might see using averted vision.
At this time of the year there is a great object to see this effect for yourself even without a telescope. The Pleiades, or Seven Sisters, or M 45, is a pretty star cluster in the constellation Taurus. These stars are currently moving through a cloud of gas and dust that makes them glow in a beautiful blue light. Use a star chart or cell phone application to find Taurus and you can’t miss the Pleiades. In November, face due east after sunset and M 45 will be about halfway up the sky. Find it? Now, look slightly away, now look back, then slightly away again. Cool, eh? This technique works in any low-light situation: You can use it in dark alleys, gloomy wooded trails, or in your backyard while taking out the garbage. As always, practice makes perfect so try using averted vision tonight.
Chris Fellows, Serenity Mobile Observatory
Find Chris on Facebook (or, if you’re lucky, at your campground). (Editor: Check out his amazing photos on his Facebook page!)