[Prev][Next][Index][Thread]

(meteorobs) QUERY: Limits of IMO LM charts?




I promise to provide a summary of my observations around the Perseid max, as 
soon as the data I laboriously transcribed from tape to paper can be laboriously 
transcribed from paper to electrons (hopefully tonight). I also hope to provide 
a juicy, detailed account of the wonder of observing from a pitch-black beach in 
the subtropics, with a southern ocean horizon letting me glimpse constellations 
I had never even identified before... Not to mention sharks and sea turtles. :)

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??

To my utter amazement, and in spite of no less than *four* recounts of this 
region on the morning of the Perseid max, I still was forced to conclude that I 
was seeing *38+* stars in this field! This in spite of the obvious zodiacal 
band, and the close-to-the-horizon crescent moon.

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?).

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?

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, but I haven't seen it 
mentioned in any of the emails or Web pages I've read. I ask, because one of the 
few downers of going out to these eye-bending dark sites is the endless, 
mind-numbing 50 and 60 star counts which have to be made every half hour...

Thanks in advance,
Lew Gramer, sunburnished meteor observer ;>