Notes from Under Sky


It's no Carly Simon tune, that's for sure

Recently, on sci.astro.amateur, there was an extensive thread about observing skills and whether or not one "sees better" as one gains experience. This was debated rather loudly—well, as loudly as you can imagine on a text-only newsgroup—until we finally came to the conclusion that the answer depends primarily on what you mean by "seeing." Perhaps that all seems obvious now in retrospect, but it still took a while.

I was thinking the other day, as I often do, and it occurred to me that people often say things like "The Cassini Division was razor sharp and wide enough to drive a Mack truck through," even though the Division only spans about half an arc second and a lot of these people's scopes don't resolve anywhere near that finely.

So are they lying? Or deluding themselves? Or do they perhaps have some superhuman power that allows them to see beyond the physical limitations of their telescopes?

Probably not. But it seemed to me that when you see something very far away, using the unaided eye for instance, you often think you are seeing it perfectly clearly, when the truth is that you can barely make it out, even when you have no idea a priori what the thing you're looking at is.

What I think is happening is that you know how the blurring works with distance, and you are able in some way to work "backwards" to derive the original, unblurred object. I also think something similar is happening in the case of, say, the Cassini Division. CCD imagers often do something called deconvolution—usually, they mean undoing the effects of fast seeing or the spreading effect of the Airy pattern. But visual observers might do that too.

What has this got to do with observing experience? Well, deconvolution or whatever you want to call it is an observing skill, and I think it's something that's integral to "seeing things," and finally it's something that I believe gets better with experience. The next time you go out and look through an eyepiece at a challenging object, try to think explicitly about the visual processing that's taking place before you consciously perceive something. Is there deconvolution going on in your life? Only you can say for sure, but I'd lay reasonably good money on it.

Copyright (c) 1999 Brian Tung