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Re: (meteorobs) QUERY: Limits of IMO LM charts?



In a message dated 96-08-19 14:38:44 EDT, you write:

<< Meantime, however, I have a very specific QUESTION about the IMO Limiting 
 Magnitude Chart #8, in Taurus. The question is, what do I do with a star
count 
 which significantly exceeds the published limit of 32 stars??
 
 To my utter amazement, and in spite of no less than *four* recounts of this 
 region on the morning of the Perseid max, I still was forced to conclude
that I 
 was seeing *38+* stars in this field! This in spite of the obvious zodiacal 
 band, and the close-to-the-horizon crescent moon.
 
 The only explanation I could come up with (barring an error in the published

 chart) was that this area of the sky was just under 7.5 lm, and that there
were 
 a PROFUSION of stars in the magnitude decile between 7.5 and 7.6 (or 7.7?).
 
 This leads to a more general question (although I won't be under these skies

 again for some time... ignore my gentle weeping): Is there any published 
 "extension" to the LM chart tables put out by the IMO, listing star counts
and 
 limiting magnitudes below the IMO's arbitrary limit of 7.5?
 
 As a MORE GENERAL question, is the AAVSO-chart method of determining
limiting 
 magnitudes still advocated by IMO for experienced observers under very dark 
 skies? It's discussed in my old copy of the IMO Handbook, but I haven't seen
it 
 mentioned in any of the emails or Web pages I've read. I ask, because one of
the 
 few downers of going out to these eye-bending dark sites is the endless, 
 mind-numbing 50 and 60 star counts which have to be made every half hour...
 
 Thanks in advance,
 Lew Gramer, sunburnished meteor observer ;>
  >>
------
Lew,
It's rather puzzling that you have an LM over 7.5.  Do you wear glasses while
you observe?  If so, perhaps there's a little bit of magnification by your
lenses.  I know Norman mentioned once that he wears glasses...I was wondering
if you do to? Also, you might be counting some of the stars more than once
perhaps? Did you have any effects with Venus or the moon? I hope your mean
magnitudes correlate with your high LM.  I believe it is Ralf
Kolfschak(forgive the spelling I think?) who often reports LM's above 7.0,
but his Mean Magnitudes often corresponds to these high LM's with them being
near +4.0 etc.  If your Mean Magnitudes don't reflect a similar pattern, you
might be cursed with a form of "tunnel vision". I know Lunsford has what I
call wide angle perception. I myself have about mid-way perception and I
suspect from what I hear from Norman he has what I would call tunnel
vision...that is he see's quite well in a narrow area.  Getting back to the
problem of not being able to have a star count area high enough for your
vision, I guess until an alternative solution is put forth, use whatever
means necessary to determine your LM above 7.5.  From your communications, I
doubt you will have this problem very often though.
George Z.