Re: (IAAC) Published magnitudes and visibility (was Re: Obj: IC 1296...)

<plus any reddening due to dust...
Hmmm...this statement doesnt make sense. I always thought that because of dust or the presence of dust, the object would reflect rather than emit, thus making the object unobservable through any type of nebular filter. This is true with portions of the Trifid, The Merope Nebula, M78 and when looking at Proto-Planetary objects, where the star has thrown off its accumulated dust into a torus around the star. The dust may hide the progenitor star of the pre-planetary nebula. Such is the case in many observable proto-planetary objects like the Egg Nebula, CRL 2688; Frosty Leo, Campbells Star, M2-9, the Butterfly Nebula, etc.
In the latter stages of life, the about to be planetary nebula first throws off its dust, then after about 10,000 years it throws off a solar wind of hot gas at about 2,000 mph which makes the  proto-PNe glow a little, but later on, a dense SUPERwind traveling around 5,000 mph is ejected at which point it encounters the previously slow wind and forms a bow shock. This bow shock is evident in all PNe we see today, giving rise to the Ring structure we see in most all planetary nebula.
So a redenning of the dust rally doesnt make sense. Just my 2 cents worth
Dave Aucoin
----- Original Message -----
From: Lew Gramer
Sent: Wednesday, August 29, 2001 6:39 PM
To: Internet Amateur Astronomers Catalog - Discussion
Subject: (IAAC) Published magnitudes and visibility (was Re: Obj: IC 1296...)

I am really enjoying this thread - thanks everyone! BTW,
I've changed the subject line (above) so hopefully this
thread will be easier to find from our archives later...

Dave Aucoin writes:
>we can see about 1.5 to 2 magnitudes [deeper] than the
>published photographic magnitues

And Doug Stewart follows up:
>I tend to agree with you. I find that many nebulae -
>especially planetaries - with only a photographic mag.
>published are far easier to see than one would expect.

This was a nice rule of thumb you cited for planetaries,
Dave! I have not heard this little formula before. For
sure, I would expect an EXACT number would have to take
into account the physics of the particular object, plus
any reddening due to dust, etc. Still, it is helpful...

For my own observing, especially for objects besides PNe
and emission nebulae, I would take this a step further:

In general, if I use published magnitudes at all in my
observation planning, I will use them exclusively as a
POSITIVE indication... In other words if the published
magnitude (in ANY band) is *bright*, I might take that
as a cue that the object in question *is* worth trying
for. If on the other hand, I see a published magnitude
which is "too faint" for my instrument and my hoped-for
conditions, then I will simply ignore it! After all, I
reason, the band in which total magnitude was measured
may or may not be properly cited - plus even V mags do
not fit MY (or anyone's) color responses perfectly...

In the latter scenario, I will tend to look rather for
indications from my fellow visual observers around the
world (both on IAAC, elsewhere on the Web, and in the
published sources), as to the object's visibility. Of
course, I am ornery enough that even if I can find NO
observations of an object from other amateurs, I will
still sometimes put it on my list for a session, if I
hope to be observing under very favorable conditions!
(Sadly, that isn't very often, living where I do. :>)

Anyway, I am far from being the most experienced deep
sky observer here, so I welcome thoughts from others!

Clear skies all, and thanks for a lively discussion,
Lew Gramer

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