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



At 12:05 20-08-96 +0200, you wrote:

>I try always to measure the Lm in two or three areas.  I usually do this
>at the beginning of an observation.  In the midst of the observation, I
>often stick to one counting area to save time, especially if the sky
>darkness hasn't changed.  My perception for meteors goes down drastically
>when I count stars, therefore I try to spend as little time as possible
>on this activity.
>
>I usually recount the Lm two or three times.  In case of discrepancy,
>I note down all measurements, and find an average after the observation.
>
>It is often difficult to determine whether stars on the border of the
>area should be included or not.  This problem becomes larger at better
>Lm-values (more and more stars on the border).  I think the Taurus-area
>is on the difficult side, since the triangle-shaped area is very "long".
>So I always try to measure the Lm in Gemini and Perseus as well, but
>of course only if the sky darkness doesn't differ by a notable amount.
>
>It is possible that the IMO-areas have been derived from AAVSO-charts.
>In that case you can try to find the magnitude of the "38th brightest
>star" yourself.  It's a dirty job, but someone's got to do it...  :-)
>
>All the best,
>Trond
>
>
>P.S. With that kind of limiting magnitude, you should go for Neptune
>sometime.  My personal record is about 7.1, and I was _really_ proud
>to achieve that one.
>Is it easy to see the Milky Way near Sirius from your place?  I saw
>it once when it was ~5 degrees above the horizon.  (Made me proud to
>see it at all, since I live on latitude 60.)
>
>
>


I fully agree with Trond's comment to count in two or three Lm-area's: this
is what I always do. I count at least once an hour, often twice, also if the
Lm seems steady: you'll find out that often it is not! Indeed, counting
distracts from meteors. Solve this by noting down a break for one minute or
two minutes to conduct a count. I prefer to miss some meteors due to a break
for a count, instead of having ambiguous data because the variations in Lm
are not clear, or underdetermined. This is especially of concern when you
are having a 'long run' of several hours. I have noted the effect (during
reduction of the 1995 Quadrantids) that observers determining only a few
Lm's during that 12-13 hour period tended to show variations in ZHR that I
suspect are due to variating limiting magnitudes, since we had those
variations in determined Lm (determined at a more continuous scale: each
half to whole hour) and less variation in ZHR. Lm- determinations are
important, think about that! It is not only (and not primarily) the number
of observed meteors that count...

I Fully fully agree with Trond's comments about difficulty with faint stars
near the area's edges. Actually, I think many of the Lm-area's are not quite
favourably chosen... One of my all time high favourits is Draco: I find this
area quite 'easy' to use, though problematic with Lm's below 6.0.

Marco Langbroek
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