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(IAAC) Re: Limiting magnitude question



Jure Atanackov posted:
> On the other hand there are frequent reports of LMs in excess of
> of 7.5, sometimes even 8.0 from deep-sky observers under dark skies. Just
> as an example - I chanced upon a naked eye sighting of M81 by Brian Skiff
> where he saw several 8.0 magnitude stars and a report from Nebraska Star
> Party in 1995 where an observer (forgot his name) saw 8.2 magnitude stars.
The individual who went to 8.2 was Dave Nash (now lives in Utah I
believe), and it was done from what I would call a "pristine" dark sky
site at 3100 ft (945m) elevation.  I can't go quite that faint even from
there (typically, its 7.5 to 7.8 for me at NSP), as Dave is somewhat
younger than I am (and had better eyes to boot).  From my deep sky
observing site here in the southeastern part of the state (40.29N, 1300
ft elevation), I can go to 7.0 occasionally, although more typically,
its something more like 6.5 to 6.8.  This level might be more in line
with the IMO method results.  I have done attempts at zenith limiting
magnitudes at times for specific areas of the sky overhead, but I
generally take a more common shortcut.  For the "general" limiting
magnitude number which goes into my logbook, I generally use a
large-scale chart of the area around the north celestial pole (5 degree
radius) with listed star magnitudes and then apply about a 0.1 magnitude
correction for extinction.  I do recall Sidgwick (AMATEUR ASTRONOMER'S
HANDBOOK, p. 26) mentioning an experiment where dark adapted observers
in a fully darkened room were able to see an artificial star with a
magnitude of about 8.5, so I have no trouble believing at least a few
people at a dark enough site could get close to this level.  Clear skies
to you.        
-- 
David Knisely  KA0CZC@navix.net
Prairie Astronomy Club, Inc.  http://www.4w.com/pac
Hyde Memorial Observatory:
http://www.blackstarpress.com/arin/hyde
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