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(meteorobs) Re: LM's and the Milky Way
GeoZay@aol.com wrote:
>
> I have an interesting paradox that has puzzled me for some while. Perhaps if I
> explain it here, someone will have some hint as to why this puzzle exists?
>
> Sometime last year, Marco mentioned that he doesn't start noticing the Milky
> Way until he gets a star count that gives an LM around 6.0. I believe Robert
> Lunsford said something similar? They both often will achieve LM's on dark
> nights in the upper 6's and above. My normal limiting magnitude that I can get
> from a very dark sky location from this method is at best around 6.0 to 6.1.
> In my case, I begin to perceive the milky way when my LM is near 5.2. These
> observers can see dimmer stars than I on a routine basis, but don't notice the
> milky way until they get a 6.0 sky. It puzzles me as to why I can't see the
> dimmer stars but am able to perceive the milky way with a brighter sky than
> these individuals with the apparent better eyesight.
>
George it is obvious that you must have a perception approximately 0.8
magnitudes lower than Marco and I. If I see a 6.0 sky you will rate it
5.2. If I see a 6.8 sky you will rate it as 6.0. It is not that you are
seeing the Milky Way under a brighter sky but rather that you rate the
LM as being lower. The sky brightness will be the same for the both of
us.
> At first I thought that my difficulty would lie in the area that some of the
> dim stars in my star count are too close together and I'm not able to split
> them for the count. But in some star count areas, there aren't any close stars
> that would effect my star count that much and still give me an LM near 6.0. I
> routinely get a near 6.0 sky no matter where I make the count. I assume it has
> something to with physiology...but can't seem to grasp in what way? Perhaps
> the overall color of light from the Milky Way is easier for me to perceive and
> still not able to pick up on dim stars all that much? Any one with any ideas
> as to why?
I believe that star count areas yield an LM that is actually worse than
reality for the reasons George mentions above. Still, it is better to
underestimate the LM than overestimate. It is interesting that George
gets an LM of 6.0 under various conditions while I can have fairly large
changes even during the course of one session. Some of my changes are
due to switching count areas during the session. For a great majority of
my sessions I achieve the best LM estimate during my first or second
hour with estimates falling perhaps 0.1 magnitude the remainder of the
night. I make LM estimates at the beginning and end of every hour using
the two closest areas to the center of my view. I will make more
estimates should thin clouds or the moon be present. I believe Lew
mentioned someone estimating every 15 minutes or up to 5 times an hour.
What a pain! To be perfectly honest I find these estimates to be tedious
and often interrupted by a meteor or two. It is valuable information
though and a necessary part of every thorough observers routine.
In summation, I believe that when George and I get together we see the
same sky brightness, the same Milky Way, but the estimated LM's will be
0.8 magnitudes apart due to different perception factors.
This has been a very interesting thread. Thanks to George for bringing
it up and to all the people who took time to respond.
Bob Lunsford
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