Stargazers: Scan night sky with these tricks


On a recent trip to Africa, I was struck by the remarkable ability of safari guides to point out even the tiniest and most camouflaged flowers, birds and animals. "How in the world did they ever find that?" I thought.

The answer, of course, is that these guides have expert knowledge of the area and have developed a few useful tricks of the trade along the way.

The same is true for astronomers. People are often amazed by my ability to find things among a seemingly random maze of stars. Of course, I have expert knowledge of the sky as well as decades of practice, but that's not the whole secret.

To excel at stargazing, we must first understand how human vision works so we can maximize the power of our eyesight.

One of my secrets is to use a process we've all experienced: dark adaptation. You know how tough it can be to find your way to your seat when you enter a movie theater on a sunny day. But after spending time in the darkened theater, finding your way in the room is no challenge. That's because, in darkness, our pupils dilate to allow in more light. This process takes time — often more than 20 minutes — but it does eventually happen.

Step back onto the sunny street again, however, and the sudden shift from dark to light can be stunning. Yet within seconds you're seeing normally again.

Astronomers always allow plenty of time for this process to occur before they begin observing. Once dark adaptation is completed, they protect their night vision by using red light when finding their way around or when using star maps or log books.

Another astronomer trick is something called averted vision. The sensors at the center of the retina are known as cones; they see colors quite well, but only under bright lighting conditions. Only rods — the gray sensors surrounding the cones — can see in faint light, but they do so at the expense of color.

In order to see faint celestial smudges more clearly, astronomers use their rods by glancing off to the side of dim objects.

Try out these techniques in a very dark environment. Allow yourself to become fully dark adapted by avoiding white light. Take a flashlight with you that is covered with red cellophane, or get yourself a red LED flashlight. Then, find some faint objects in the sky and avert your vision to see them.

For viewers located in the Northern Hemisphere, one of the best ways to test these techniques is in the northern sky: the Little Dipper. Choose one of its faintest stars and force yourself to stare directly at it. What happens? It vanishes. That's because you're trying to force the cones to work; gaze slightly off to the side of the star and let the rods do the work, and you'll see the star.

Unless you're an astronomer, you probably weren't aware of the tricks used by us "night people." But you are now. So no more excuses — get out there and enjoy those feeble photons raining down upon us from afar!

Visit Dennis Mammana at


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