Hi PGC,
Quote:
Originally Posted by pgc hunter
Another fantastic report. Shame about the smoke though....I can't tell you how much I HATE those burnoffs! All of Autumn was ruined here, along with several clear nights.
Nice job with "PGC 8451", mag 16.5 wow! I'm guessing that's one of the faintest galaxies you've ever seen?
Love those small HSB PNe's.
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Re the low magnitude -- the short answer is I dunno. But as said before here and elsewhere, I pay little attention if any to faint/ultra-faint magnitudes because a very substantial majority of them are rubbery to say the least. This one is no different. I've recorded a number of eg's that according to Megastar or Deepsky or other sources are worse than mag 17 and in a friends 50cm we've seen a few in the 18's but they are plainly in error or bear little relationship to a true visual magnitude -- because they were nowhere near ultra-tough to see.
Here's a couple of examples that demonstrate the problem.
Hickson 48 is a small group of galaxies near AGC 1060 (Hydra I) in Hydra. Hickson 48C (PGC 31577) according to Megastar is mag 16.4 and 48D (PGC 31580) is 17.0. Where did those magnitudes come from? Megastar provides a source for the data -- the PGC and it is a good chance in turn they came from the CGCG. How were they measured? At what wavelength? These answers are not easy to discover. The former is visible faintly in 31cm but not the latter -- which can be seen in 46cm and while faint is not a huge stretch (both assume a very dark sky).
Now, I have had a poke around in SIMBAD (have I mentioned before how much I hate the SIMBAD interface?) and it isn't terribly helpful (well immediately helpful) on magnitudes for these two. It does provide some radio flux brightnesses however ...
Sky-Map does not provide a magnitude. Nor does DeepSky. Deep Sky Browser does and they confirm the ones in Megastar and prefix them with a "p" indicating that it is a photographic magnitude but how reliable is that for visual purposes?
So, a poke around in NED however did produce something helpful -- one of the earlier papers from 1989 here:
http://articles.adsabs.harvard.edu/c...;filetype=.pdf
which is a full photometric catalogue of the Hickson groups by the astronomer (Paul Hickson + a few others) who originally compiled the catalogue in 1982.
Now scroll down to P7, Column 8 Hickson 48 and you will find they have photometrically measured B mags of 16.52 and 17.48 -- now at last some useful information. There is an equation/relation somewhere I can't presently lay my hand on that converts these to visual magnitudes but there is a handy rule of thumb (very reliable) that also simply says add 0.9 magnitudes (to make it brighter) and that is a very good v mag approximation.
From that we get approximations of v15.6 for C and v16.6 for D. Those figures are consistent with their eyepiece appearance (well my experience) and are pretty reliable -- they are also somewhat different from the 16.4 and 17.0 we started with and we still don't really know where they came from or how they were measured.
As for all the other faint galaxies in the sky -- the overwhelming majority you won't be so lucky after a 1/2 hour NED/SIMBAD/Sky-Map/Deep Sky Browser interrogation.
The moral of the story is this -- if it's a faint magnitude and you don't know how it was measured, treat it like it is made of rubber. It is a guide no more. You could if you wish have a trawl through the papers etc and maybe just maybe find something truly useful but for many its a long-shot.
Re the PNe -- well my own taste is for the larger difficult PNe (like the Abell catlogue) -- but each to his own. I don't spend a lot of time tracking down near stellar ones that are more of a test of finding skills. For me, not as interesting as the ghostly ones.
Best,
Les D