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(meteorobs) ZLMs
Hi folks, from down under in NZ!
Recently, there has been some discussion about extended limiting
magnitude estimations for VERY DARK skies, so I thought I's submit my 50
cents worth... particularly from Lew Gramer, which I understand, has
already been answered by several meteor workers.
I have never been a fan of the IMO "triangle" method of determining
Zenith Limiting Magnitudes (ZLM)... a term I think I coined about 5
years ago, instead of the more popular but sometimes confusing "LM"
term.
Alastair McBeath (IMO VP) and I, both independently use star charts
such as the AAVSO for our ZLMs, as this seems easier to HIM and ME to
use. The AAVSO Atlas goes down to Mv 9.5, which is well beyond the
current world record of 8.6 held by Sephen James O'Meara of SKY &
TELESCOPE, from Mauna Kea (and that's a CONSISTENT 8.6!!!). I have
managed a ZLM of 7.4 from Black Birch 1290m, and Mt John Observatory on
May 11-12 (-23 C with chill factor!) at 1030m, with a ZLM of 7.2 for
some 2.5 hrs. It is claimed in SKY & TELESCOPE, that the late Gerard
Kuiper (of KAO fame) could see down to 7.6 well into his 70's. I once
saw 12 pleiades from New Zealand, on Mt Brewster in the Haast Valley at
about 5,000 feet, in May 1965, as a young boy, when there was a 25 deg
F frost.... brrrrrr! Steve O'Meara's record (which is the best this
century) is 16, and the all time record is 18 pleiades. Ralf Koschack:-
an IMO Councillor from Germany, and a former director of the IMO VMDB
before Rainer Arlt, frequently sees ZLMs of 7.0 to 7.5.
Scientifically, it not only has to do with the dark skies itself, but
also the actual diameter of the human eye pupil, which varies from
person to person. Dark adaptation is usually complete, I find, after 40
minutes, certainly an hour. I usually find that my clearest skies in NZ,
usually come a couple of hours after a good solid rain shower, which
predictably washes out the atmospheric crud.
O'Meara's pupils have been medically checked, and are abnormally large,
so were Kuiper's. Maybe the explanation lies there, I suspect.
Anyway, folks... use whatever RELIABLE system you wish, but remember,
that the AAVSO goes down to 9.5, and even O'Meara can't reach THAT!
About three years ago, for Southern observers, I invented a magnitude
sequence for ZLMs, using the Southern Cross, that goes down to 10.0.
During the winter months, in NZ, the Cross is on the Zenith in the
early evenings. For Summer months, I am preparing a ZLM 10.0 sequence
around the "stinger" of Scorpius, and hope to publish this soon.
Remember, the ZLM relates to the ZENITH SKY, not the radiant sky...
don't get the two mixed up.
OK, I'm out of here. Any reactions under 100Mt, please to Mt
Erebus, R.D.2, Antarctica, where the North-Westerlies should hopefully
keep any fall-out well away from Wellington.
Any people ou there who would like me to make some proposals,
suggestions, ideas, comments to IMO Council (we have our next meeting at
Apeldoorn, next month) drop me a note by e-mail, as I am an IMO
Councillor. We want as much input from around the world as possible.
Your comments can remain anonymous and confidential if you wish.
Brick-bats are just as welcome as boquets. WE on IMO Council want to
serve you as well as possible, and would appreciate YOUR feedback. let
us know what you want, don't want etc. WE are YOUR servants out there,
and if we are to properly administer global meteoritics, then we need
global feedback and input.
Looking forward to hearing from you, and acting on your comments
Proudly in the service of global meteoritics
Your kiwi buddy and meteor collaegue
GRAHAM WOLF
New Zealand