Friday 15 February 2019

Understanding Nebulae - Part 3

Getting the MOST out of your HUMAN eyes

Ok, we now know that our eyes are not the best at low levels of light. But, did you know that our eyes also have different areas that are more and less sensitive in low levels of light? That the less sensitive area to light holds both the greatest number of colour receptors and is also where we see things with the greatest detail - central vision. That the area that is most sensitive at low levels of light is also the area where less detail is seen - peripheral vision. AND that there is a sweet-spot between these two areas of our vision where we get both detail and light sensitivity!

This sweet-spot around our central vision is the area that we as observers need to use to maximize our capability at the eyepiece.

Here's an everyday example to demonstrate what I'm talking about. You are in your bedroom at night with all the lights off. Only a feeble light is visible illuminating the room. Have you noticed that when you look around the room in the dark, when you look directly at something that it somehow "disappears", but as soon as you look away to one side of that thing it somehow "reappears"!? The good news is two-fold - 1, you are not going mad - it's how our eyes actually do work; 2, it is this very feature of our eyes that we use at the eyepiece!

Looking at things this way, just to the side and not directly, is called AVERTED VISION. It is using that sweet-spot area around our central vision where there is a rich mix of both rods and cones as the central vision transitions to our peripheral vision. It is this area where there is that all important low light area of our vision where we get both detail AND low light sensitivity.

THIS is the one trick to maximizing our experience at the eyepiece!

Do not look directly at the object, but just to one side of it!

The good thing about using AVERTED VISION is it takes only an instant to learn, and only moments to master! You've been using averted vision all your life in dark rooms/environments, and you've never been aware of it!

Below is a little example of how to utilize averted vision. The object in question is a globular cluster. Our immediate response is to look at it directly. That is fine with this sketch. But through the eyepiece, so see a globular cluster in all its splendour with its many thousands of stars all so clearly visible and individual, you DON'T LOOK AT IT DIRECTLY, but just to one side as indicated by the X. It can be to the left or right of the object, it doesn't matter. It just needs to be just off to one side.

Tip in locating objects

You may have also noticed another VERY ANNOYING thing when using your scope. When you are trying to find a faint object you are panning the scope from side to side, and you catch a glimpse of something faint and fuzzy out of the corner of your eye, but when you pan the scope back to that faint thing YOU CAN'T FIND THE BLASTED THING!!!  😡 This is because you are now using your central vision to spot that faint thing, when it was your peripheral vision - your most light sensitive vision - that spotted that thing.

The solution is an easy one, but a bugger of one to learn - DON'T LOOK FOR THE OBJECT while you pan the scope back!

This is a really easy thing, but a bugger of a trick to remember, and it still catches me out after 35 years of using telescopes! 😄 It is also totally counter intuitive to how we use our eyes every day. But it all has to do with the way our eyes work that I described above. If it was your peripheral vision that spotted that faint thing, then it must be your peripheral vision that needs to be used to reacquire it!


I hope these three article specific posts have been helpful to you as you start on your astro experiences. Many people become frustrated with astronomy because they don't understand how our eyes work, how to exploit their strengths, and the unfortunate expectations that the pretty pictures create in our minds. But astro can be a very satisfying experience. Just that as with all things we do, such as walking, driving, playing a sport, it takes time and understanding to make the most of these. Astro is also a quite pursuit, not a "smash'n'grab" one. Like a said earlier, rush things and you will miss things. Slow down, calm your heart, and the Universe will reveal itself to you!  😊


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