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Re: (IAAC) [amastro] Re: limiting magnitude at WSP
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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