Tricks Astronomers use to see Stars Best
by Bryan Schaaf
Rest: Get some rest before going out to observe the stars. A brief nap
can help your eyes relax and later perform better in the dark. Avoiding very bright lights
or television in the evening before leaving home helps, too.
Dark Adaptation: Once you are at the observing location, look at the
night sky. At first you might not see much, but as your eyes adapt to the dark you will
notice many more stars. It takes up to an hour for your eyes to become dark adapted and
that means you will see light that's 200 times dimmer. Your dark adaptation can be ruined
almost instantly with any stray light, so avoid lights to protect your night vision.
Averted Vision: Eyes are very sophisticated. Each eye has a sensor
array called a retina. Inside the center of the retina are sensors called cones. Around
the cones on the periphery of the eye are rods. Cones are great for sensing colors and
fine detail, but they are poor for detecting faint light. Rods are great for detecting dim
light, but fail at sensing colors and details. Rods provide a wide angle of vision even at
night. Astronomers use this knowledge to optimize what can be seen.
Instead of looking straight AT an object, look to the SIDE out the corner of the eye.
The rods will allow you to detect a faint object in the telescope view that otherwise
might be missed completely. This is called averted vision.
Image Scanning and Induced Motion: When viewing a telescope image
sometimes the object or objects, such as a galaxy cluster, is too faint to see even using
averted vision. It often helps to move your vision around in the field randomly. Sometimes
this method will cause a faint object to suddenly appear in the periphery of vision. This
can also be achieved by gently tapping the telescope tube to induce a motion of the image.
Motion can often bring out the faint, nearly invisible objects, much like a deer in the
woods, for instance. When a deer stands still it's colors can blend into the surrounding
vegetation, but it can often be detected when it moves.
All of the above tricks to see the stars best have to do with the
ability of the brain and eyes to work together. Your eyes' sophisticated lens system sends
an upside down image to the sensors of the retina, similar to the function of a camera or
telescope. Your brain inverts the image for you. Also, the brain tends to correct other
defects that the lens sends to your retina. The eye-brain combination can be trained to
see very dim light or detect subtle differences in light level or color. The more
observing you do the more you will see! Patience and practice are the keys that make
amateur astronomy fulfilling.
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