Hi there. You posted:

Charming, isn't it, how wildly the experts vary? Let's say that
the dream sky, which can be approached but never equalled on Earth,
is mag 22 per square arcsecond. Knoll/Schaefer places the NELM
for that sky at 6.6, Blackwell/Clark at 7.2, and Ferris at 8.0.
FWIW, under my customary decent rural skies -- surely no better
than mag 21 per square arcsecond, if that -- I have seen stars
to mag 6.8 or 6.9, but I have done no better at all under far
darker and clearer skies out West.

Much of what we are seeing here is variation in the sensitivity of eyes rather
than the lack of consistency found with "experts". However, there are very
real variations in the quality of sites when it comes to ZLM of the eye. At
my local observing site, the unaided eye ZLM is often in the 6.5 to 6.9 range.
Last week at the Nebraska Star Party, I did a quick star count in and around
the head of Draco and checked the stars visible against the data in Megastar.
One very faint star I detected surprised me, as it turned out to be
magnitude 7.59! I do know that others with better eyes have gone fainter from
that location, and this is documented in various places (the record appears to
be Dave Nash's 8.2 at the 2nd Nebraska Star Party). I can't go fainter than
7.8 even from NSP, but the sky is clearly better than what I get at home.
Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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* Attend the 10th Annual NEBRASKA STAR PARTY *
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