09Mar2012

Techniques For Better Viewing

Some tips on using your scope to better advantage

How do you get the most out of using your telescope? Astronomers have been collecting and swapping observing tips for years. Here is a brief description of some popular recommendations from selecting an observing location to observing with a telescope.

Don’t observe near or within the unsightly glare of outdoor lights such as floods, mercury vapor “yard blasters” and wall packs to name but a few. Even better yet, put your telescope in the car and take it to a location outside of town. Make certain you have the property owner’s permission before doing so.

Likewise, the light from a bright moon may interfere as well. When viewing faint objects you might want to wait for a night that the moon’s not up or at least is merely a crescent.

If your telescope has a small finder scope attached, make sure that it’s aligned parallel to the main telescope before using it to locate celestial targets. First choose a distant terrestrial object, such as a roof peak by day or a far off light at night. The target object should be at least a couple of blocks away.

Using the lowest power eyepiece, locate the target object with the main instrument. Once it’s found, lock the knobs on the two axes so the telescope won’t move. Adjust the small thumb screws on the finder scope until the object is centered in the cross hairs and re-tighten them. Check the main telescope. If the object not centered, unlock the axes, re-center and repeat until the object has been centered in both scopes.

Now you’re almost ready to observe. Dark adaptation occurs as the eye recovers its sensitivity after exposure to light. Let your eyes adjust to the darkness while avoiding any white lights or flashlights. Ten minutes is enough to recover a fair amount of night vision and after a half hour the adaptation will be mostly complete.

When referring to printed charts and reference materials, or making notes, avoid white light flashlights. Use a red filtered one instead. The eye’s rods are insensitive to red light so your low level night vision will not be affected.

Distant galaxies and far off world's await the curios

In a pinch, try using a rubber band to fasten one or two layers of brown paper from a grocery bag over the end of the flashlight. Begin viewing each new object using your lowest power eyepiece. Don’t automatically jump to the highest powered eyepiece in your collection. Among different power eyepieces of similar design, low power views tend to be brighter and have a wider field including more of the sky.

Anyone that has looked into the eyepiece at faint nebulae or galaxies through a telescope — no matter how large — immediately realized the views are not the same as the beautiful full color images taken with the Hubble Space Telescope. The reason is because images are created with time exposures on film or electronic detectors that allow light to be collected over time. Our eyes don’t work that way.

The eye’s retina has cones and rods. Cones allow us to detect color but in order to do so require more stimulation than a faint telescopic image usually provides. The rods are more sensitive but see in black and white. The rods are the workhorse when it comes to viewing faint objects.

Averted vision is a technique for directing an image to fall upon the rods where it is most effective. Because the rods are not located at the center of vision, the trick is to direct the vision slightly off to the side by not staring directly at the object. In doing so, the faint image may pop out and be visible, yet disappears when one looks straight at it using the cones.

American author Edgar Allan Poe was aware of the physiology behind averted vision. The following description is from his 1841 short story “The Murders in the Rue Morgue”:

“To look at a star by glances — to view it in a side-long way, by turning toward it the exterior portions of the retina (more susceptible of feeble impressions of light than the interior), is to behold the star distinctly — is to have the best appreciation of its lustre — a lustre which grows dim just in proportion as we turn our vision fully upon it. A greater number of rays actually fall upon the eye in the latter case, but in the former, there is the more refined capacity for comprehension.”

Another technique for seeing seemingly invisible faint objects is a light tapping of the tube, causing the image to jiggle. The eye likes motion and once the image is detected after a slight rap on the tube, your averted vision may be able to hold the image steady.

Several of the above tips are valid whether or not you have a telescope. So get outside, as Poe wrote, “to be enamoured of the Night for her own sake.” Source: Carroll County Times

 

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Dave says:

Good point Tim. I’ll run a separate story on this in an upcoming issue. (Ed.)