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Re: (IAAC) [amastro] Re: limiting magnitude at WSP
I concur with you comments about seeing objects (images) after one's
attention is directed to the subject. A prime example is some star field
photos that I have been examining with a low power microscope. Many of the
deep sky objects were missed until reference was made to an atlas. They were
definitely there at first pass, because I can see them now that I know they
are there. There is nothing imaginary about the images on the photos. As you
mentioned about the way the optics are wired to the brain results in
misrecognition. The skill gained in repeated observation is another good
example of expectations overcoming the nonrecognition/misrecognition
phenomenion. It is long established that there is a real difference in the
way we individually see or interpret vision. It's referred to as the personal
equation.
Dan Duriscoe wrote:
The National Park Service is beginning a program of night sky brightness
monitoring
with the objective of protecting dark sites in national parks. One of the
methods
we propose to use is limiting magnitude estimates by human observers. We are
particularly interested in any information and/or previous research that has
been
done on this method. I personally find that I do indeed find a few more
stars in
any given field if I know where to look for them. However, I have never
considered
this as "bias", merely a physiological peculiarity of the human brain/eye
interface. If you know what and where to look for something you're chances
of
finding it are much improved. I don't think it means that you are actually
"imagining" that it is there. Am I wrong?
Dan Duriscoe
Sequoia and Kings Canyon National Parks
Lew Gramer wrote:
> Alex Langoussis writes:
> >Your mileage may vary. When comparing skies at different observing
> >sites, I would think the best results would be obtained by the same
> >observers using the same scopes at the different sites.
>
> This is key, Alex: using unaided-eye Limiting Magnitude as an analog, two
> observers on the same night at the same location, with the same full (40+
min)
> dark adaptation, can differ in their LM as much as a full magnitude.
>
> And in fact, for the same INSTRUMENT and conditions, I'd be interested to
hear
> what relationship holds between unaided and telescopic LMs across a sample
of
> several different observers. With all-important individual variations
accounted
> for, I suspect these two numbers are pretty well linked.
>
> BTW there is one problem with the sorts of charts published in S&T, and in
the
> excellent guidebooks of some of our 'amastro' participants: unintentional
bias.
> Particularly with estimates using intermittent averted vision, there seems
to be
> a tendency for HONEST and EXPERIENCED observers to "see" what they know is
> there, even if strictly speaking it is not really visible.
>
> To completely avoid this, you have to sample multiple preselected,
well-defined
> star fields in a session, and to do "double-blind" estimates: either
plotting of
> the field without prior knowledge, or simply counting stars in the field.
>
> Lew Gramer
>
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