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Re: (meteorobs) ZLMs
Graham Wolf wrote:
>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
Thanks for confirming that using the AAVSO Atlas *is* still an acceptable
method of finding LM for darker sites, Graham. And thanks for a right
gentlemanly response at that! :> As for getting feedback, here's my humble
US$17.32:
I guess George's point about measuring the LM in various areas of one's FOV
(possibly including the zenith) is well-taken: the obvious solution here is
to have a whole array of "comparison regions" peppered around the sky, each
with its set of well-separated and easily identified stars from 6.0 (or
thereabouts) down to 8.5 or whatever limit your most optimistic dreams will
take you to.
Then the standard operating procedure for this type of LM measurement would
be to check at least three or four of these "comparison regions" in
different parts of your FOV, and maybe toss in the occasional star count
too, if the skies aren't too dark nor the counts too high...
Seems like with a simple comparison pattern to work with, observers could
actually take MORE limiting magnitude measurements per hour, over more
regions of their sky! Sounds to me like this actually might be *more*
accurate for the experienced observer, especially considering the impact of
those endless counts on observer attention, and the possibility of
miscounting even on double-counts.
Not to mention it'd make dark-site observing a WHOLE lot more fun! :>
There's obviously some danger with this "comparison method" for newer
observers, who may easily misidentify particular stars, or even whole
comparison patterns! So for new observers, the current IMO charts would
seem to be best. Followed maybe by a gradual "switch-over" period for
intermediate obsevers, where their comparison LMs were ignored in favor of
their "count LMs" for analysis purposes?
Last but not least, for crap-on-a-stick sites like my beloved local "Pink
Sky Site", it probably doesn't matter a whole heap WHICH method you use...
Except that it'd be a lot harder to find comparison regions with closely
spaced stars that could cover ALL of the magnitude deciles from say 5.0 to
6.0! So probably for any sky under about 6.0 (or 6.5?), the IMO charts
would win out again.
Whew! Anyway I hope this ear-bending helps out (not to mention makes sense).
Clear (and REALLY REALLY DARK) skies to all!
Lew
PS: By the way, Graham, does the "Z" in your "ZLM" refer to the fact that
the LM correction on ZHR actually corrects for the LM at the Zenith
somehow, as opposed to where the observer is really looking? Just curious
about that one. -L
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Karen Simmons & Lew Gramer lewkaren@tiacdot net http://www.tiacdot net/users/lewkaren
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