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Re: (meteorobs) Light Pollution
To a thread about light pollution, Lew Gramer wrote:
>> [Description of Long Key observing with with LMs of 7.5 or better...]
>>One last disclaimer: I've never yet been to West Texas, to see the deadly
>>dark skies where some have supposedly measured LMs in the 8.5-8.9 range.
>>When I do someday get there though, I sincerely hope to find it is truly
>>THAT MUCH darker than my beloved Long Key site. We'll see!
And George Gliba responded:
>I flatly don't believe anyone anywhere can see LMs in the 8.5-8.9 range with
>the naked-eye. Surely this must be a typo of 7.5-7.9! I think 8.5-8.9 LM is
>impossible to see by anyone anywhere.
I know it is pretty mind-boggling, George. But I know for certain that Stephen
James O'Meara (of Comet Halley and S&T fame) has logged stars well into the 8s,
using a kind of double-blind trial involving sketches of certain tiny sky areas,
later compared with photometric sequences. As for impossibility, I can clearly
recall as a kid reading in astronomy books from the '50s that it was "physically
impossible" for humans to see stars fainter than mag 6! ;>
By the way, it must be noted that these do *NOT* constitute true "Limiting
Magnitude" estimates in the IMO sense. O'Meara and others - see the book _The
Starry Room_ by Fred Schaaf! - were seeking to record the very faintest stars
they could perceive BY ANY MEANS, so long as they were confirmable.
By contrast, the purpose of an IMO LM measurement is to determine the faintest
stars which the eye's extrafoveal area will pick up in the course of "natural"
sky gazing... Now this seems to mean different things to different people, but
to me it means the stars which you might easily spot "out of the corner of your
eye" if they suddenly started to move at meteoric speed.
The criterion I use for this - based on some advice from experienced observers
like Bob Lunsford, Norm McLeod and Rainer Arlt - is simple: if I can see a star
without straining for more than 50% of the time, using either unconcentrated
averted vision or direct vision, then I count it! If not, not...
Clear skies all,
Lew
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