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Re: (IAAC) limiting magnitude

At 03:42 PM 3/3/98 -0500, you wrote:

>If Brian Skiff 
>doesn't have time to comment on this thread right now, you can still read
what 
>he has to say in this book. :) The tough part is finding a copy now... It 
>appears to be out of print.

It is out of print - according to Skiff - but a deal is being worked on to
get a re-release in softcover or else another printing of it done sometime.
I have been looking for a copy of this book for some months now, but have
not found one. Anyone have an extra?

>By the way, your experience is quite different from mine, Jeff. I generally 
>find magnitudes commonly quoted in, e.g., NGC, IC, UGC, MCG, and Zwicky 
>catalogs are pretty hard to interpret for my observing! I can sometimes
guess 
>from the general magnitude RANGE whether an object will be visible with a
given 
>scope and sky: 

I hear you here - I get tripped up on the sizes more than magnitudes,
though, which as we already mentioned are not very useful for visual use.
Using size and magnitude together I can get some idea of what to expect to
see in the eyepiece, as long as the numbers are good. It is not too often
that the two come together, it is true.

>Anyway, based on these numbers, an observer might have expected the two
objects 
>to appear somewhat similar... In fact, my logs didn't bear this out: I
logged 
>n710 as "one of the brightest members of 262", difficult to distinguish
from a 
>star but still an easy direct vision object. n717 on the other hand was
"only 
>visible to averted vision" and "largely featureless". 

In cometary observation, we have something called the Degree of
Condensation, a 1-10 scale, which tells how starlike or how diffuse a comet
is. Something like this would be useful for galaxy observers, too.
Obviously, strongly condensed galaxies have been, in my experience at
least, easier to see than diffuse ones.

>An even more telling example was an observation of the mighty Abell 1367 in 
>Leo's haunches a year ago: IC 2955 is quoted at V=14.0, while nearby NGC
3862 
>has V=12.7. But my logs actually show IC 2955 as appearing the BRIGHTER of
the 
>two that night, in that scope... My full log is at:
>    http://www.tiac.net/users/lewkaren/netastrocatalog/msg00174.html

Interesting observations!

Both of these galaxies are in the RC3 catalog, which give some interesting
numbers:

IC  2955  Mean Surface Brightness 12.59 mag/sq arc min
NGC 3862  Mean Surface Brightness 14.53 mag/sq arc min (in B)

This certainly supports your observation. Also, some interesting numbers
from the PGC - which has *very* accurate integrated magnitudes for these
objects:

IC  2955  15.1 mag
NGC 3862  13.7 mag

Off the top of my head I can't recall which system PGC magnitudes are in,
but I strongly suspect they are P. I will leave it to the reader to
determine which metrics are more useful at the telescope. :-)


--
Jeff Medkeff          | Acting Assistant Coordinator
Rockland Observatory  | Association of Lunar and Planetary
Sierra Vista, Arizona | Observers, Solar Section

On the web at http://shutter.vet.ohio-state.edu/
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