Stephan's Quintet=Hickson 92=NGC7318+
Aug 29, 1998 ~1:40am MST
10" f/4.5 Newt
Seeing 3/10, very soft seeing; NELM=6.7
Finding the Quintet is trivial, being very near the bright 'signpost'
galaxy NGC 7331 which is interesting in its own right due to its numerous
companions and field galaxies. Four of the closer companion galaxies are
easily visible from a dark site with a 10", with a few more popping out
from time to time or at least making the observer suspicious of their
presence at times. Ranging out as far as a half degree from 7331 reveals
many more faint galaxies, especially in a large scope; but more to the
point if the direction is south and slightly westwards, one comes upon
Hickson 92 = Stephan's Quintet.
The Quintet is one of the more famous of deep sky objects, which means of
course that as a planetary observer I had never carefully observed it
before. This object proved to be easily seen in the 10", and was quite
visible in the 4.5" Newt as well, though obviously its morphology was quite
resistant to vision in the smaller scope. I quickly abandoned the small
instrument in favor of making a sketch in the larger one.
Stephan's Quintet pays large dividends to the observer who spends a lot of
time looking for the details. Initially, the group appeared to consist of
only a few evenly-illuminated whisps of light among a smattering of stars.
The thrill of observing such an object is, it seems to me, solely in the
detection. But I have never been one to settle on what is first shown to
me, so I persisted in observing the galaxy cluster in the hopes that
different magnifications or the employment of more advanced techniques or
tricks might reveal more to me.
Quite a bit of time was needed to sort out what was visible, and I finally
concluded that a group of five small galaxies arranged in the boundaries of
a parallelogram were apparent. (Later checks of SkyMap revealed the
galaxies seen were 7317, 7318a+b, 7319, and 7320.) Separating 7318 into
its two components was very problematic and never really achieved; I never
succeded in seeing them as anything but a sort of overlapping, barbel shape
with brighter, fatter areas extended roughly east-west, and a fainter area
in the middle.
As I observed the Quintet longer and longer, though, it became apparent
that all of the galaxies were, to differing degrees, slightly brighter in
the middle, and not quite evenly-illuminated after all. After some time
looking specifically for brightening, I decided that all of them showed
very subtle condensations in their centers. None of them sported stellar
nuclei, but the seeing was very soft and such were likely to be missed even
if present.
After about 30 minutes carefully looking at the field, I began to sketch.
Unfortunately, as seems to inevitably happen, the contrast in my sketch is
greatly exaggerated, but does get across the gist of what I observed.
Filling in the galaxies themselves was simple, having been amply prepared
by about a half hour of careful looking prior to picking up a pencil. I've
been working on my smearing technique after some admonitions by Brian
Skiff, and with some additional teutelage by another advanced Arizona
observer, Rik Hill, I think things are improving in this area quite a bit.
After depicting the barely-visible brightness gradients and smearing out
the outer regions of the galaxies, I turned toward the larger field to
provide some context.
The problem with sketching the surrounding stars is that as you look for
them, more and more pop into view. When I started looking, I never would
have suspected that Pegasus was a place where I would find rich starfields,
but if faint stars count as a contribution to richness, then I guess
Stephan's Quintet is in a rich starfield. I eventually abandoned the task
of recording all the stars, and instead settled on depicting the brighter
ones, and the ones in interesting positions relative to the galaxy cluster.
As I sketched the surrounding starfield, a noticed that one star repeatedly
appeared to be a little fuzzier than the others. After about ten minutes of
struggling to see this faint "star" for what it was, I decided to plot it
as another fuzzy patch, on the grounds that my eyes deserved the benefit of
the doubt. This proved fortuitous: this is plotted as NGC 7320C in SkyMap
Pro, and appears quite clearly in photographs of the Quintet, as I
discovered later. It must be a vanishingly faint galaxy, as it is definitly
on the limit for my 10", at least for last night, perhaps being visible
only 20% of the time, and visible as fuzzy even less than that.
As the observation wore on, the seeing got worse and worse, and instead of
continuing to plonk around with deep sky objects I decided to pack it in.
An observation of Jupiter or Saturn would have been futile under the
circumstances, as brief parting glances at each showed.
This afternoon, I scanned my sketch (which made the boosted-contrast
problem even worse) and attempted to smooth it a little to better
approximate the original (mostly, that was a futile effort). Comparison
with the DSS is quite favorable, which was a welcome result as earlier this
year I rather screwed up a sketch of Hickson 79, putting a bright component
galaxy in completely the wrong orientation.
Jeff Medkeff's home page.
Jeff's astronomy pages.
Copyright © Jeff Medkeff, 2002, All Rights Reserved.