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Re: (meteorobs) Bob Lunsford's Suggestions/Help & Nov. 19/20 Correction

This is definitely a shortcoming of the current count-area based LM estimating system suggested by IMO. Several other problems with it are: (1) Difficulty of determining if a faint star near the edge is inside or outside of the artificial boundary of the area, especially using averted vision (2)  If you are under dark conditions, the number of faint stars near your limit in a region is large and/or close spaced and it gets difficult to make an accurate count, again particularly using averted vision. (3) There is no smooth transition in LM, since each star counted results in a step-wise change in LM, which is not realistic. (4) You waste a lot of time to struggling with these difficulties every time you need to re-evaluate the LM during a session, which may discourage people from doing that and be detrimental under changing conditions.

I use the simpler system of just finding a sequence of stars covering the range of LM expected, in 0.2 mag steps. I use Tycho2+Bessell corrections, the most accurate available for brighter stars. I need just a half dozen stars or so, which are easy to keep track of, and I get a very accurate and continuous estimate based on which star I can just see with moderate effort by averted vision. I can re-check the LM frequently and effortlessly during my session without interference of even counting the meteors.

I would highly recommend IMO discard the count-area based system with a simple one like I use.

Mike Linnolt (LINMI)

--- RainerArlt <rarlt@aipdot de> wrote:
> At low limiting magnitudes, there are severe gaps in
> the
> conversion tables from star count to LM. This is of
> course
> since not every tenth of a magnitude is 'occupied'
> by a star 
> in the count area. You will often encounter a
> significantly
> lower LM in one of the counts made the same time. A
> count 
> in area #4 of 7 stars may be 5.1, but since the next
> star is at
> something like 5.8, the LM could have been also 5.2,
> 5.3, 5.4,
> ... 5.7 with the same count in #4.
> 
> I'd suggest to use the highest count for each time
> and average
> these (unless LM better than say +6.0). In your
> example, this
> would come down to
> 
>    07:06   5.5
>    07:27   5.9
>    07:50   5.3
> 
> AVERAGE    5.57
> 
> The method of course requires that enough star
> counts are made
> during the observation and that -- most critically
> -- several
> areas are counted.
> 
> Please note also that updated LM conversion tables
> based on
> the Tycho catalogue are available at
> 
>      http://www.imodot net/visual/lm.html      or
>     
> http://www.amsmeteors.org/imo-mirror/visual/lm.html
> 
> 
> Best wishes,
> Rainer
>
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