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



At 02:35 PM 8/19/96 -0400, Lew wrote:

>Meantime, however, I have a very specific QUESTION about the IMO Limiting 
>Magnitude Chart #8, in Taurus. The question is, what do I do with a star count 
>which significantly exceeds the published limit of 32 stars??
>The only explanation I could come up with (barring an error in the published 
>chart) was that this area of the sky was just under 7.5 lm, and that there
were 
>a PROFUSION of stars in the magnitude decile between 7.5 and 7.6 (or 7.7?).

Wow, what a problem you had...makes my 5.8 LM skies seem like downtown
Charleston! If it was me, I would probably list the lm as 7.6 and make a
note about it in the report.

>This leads to a more general question (although I won't be under these skies 
>again for some time... ignore my gentle weeping): Is there any published 
>"extension" to the LM chart tables put out by the IMO, listing star counts and 
>limiting magnitudes below the IMO's arbitrary limit of 7.5?

None that I know of...(?)......perhaps a project for an underworked NAMN
administrator... ;>

>As a MORE GENERAL question, is the AAVSO-chart method of determining limiting 
>magnitudes still advocated by IMO for experienced observers under very dark 
>skies? It's discussed in my old copy of the IMO Handbook...

The star count areas should be used when possible, but this "older" method
may need to be reverted to in those times like you experienced. I would say
at those times, check the AAVSO charts, just be sure to note it in your
report. But when the lm is back down to what us "normal" observers get, I
recommend sticking with the star count areas.

Welcome back... :)

Mark Davis
MeteorObs@charlestondot net