(IAAC) Obj: M92 - Inst: 17.5" f/4.5 Dobsonian
Observer: Lew Gramer, Steve Clougherty
Your skills: Intermediate (some years), Advanced (many years)
Date/time of observation: 16/17 May 1999 0200 UT
Location of site: Myles Standish State Forest, MA, USA (Lat 42N, Elev 5m)
Site classification: Rural
Sky darkness: 6.9 <Limiting magnitude>
Seeing: variable 8 to 3 <1-10 Seeing Scale (10 best)>
Moon presence: None - moon not in sky
Instrument: 17.5" f/4.5 Dobsonian
Magnification: 125x, 220x, 285x
Object category: GlobularCluster
Object class: IV
Object data: mag 6.5 12.1m* size 11.2
Taking advantage of a cirrus-y sky tonight to view "well known" objects,
Steve and I decided to swing his excellent new 17.5" TeleKit over to the
"lesser" Messier glob in Hercules, M92. Imagine my surprise when a quick
look at this Chestnut turned into a loggable and quite interesting obser-
vation! For before we even increased magnification on this great gorgeous
globular, a contrast effect of the hazy sky suddenly showed me one of the
starkest and most evident "dark lanes" I've so far noted in any globular!
It was exactly as though God had taken a cosmic butter knife and "halved"
the inner 1/4 of the globular - basically the entire bright core. I have
made it a sort of observing program of mine to search out globulars which
display these "dark lanes" under any observing conditions. They're inter-
esting to me because of course these clusters do not ever contain enough
REAL dust to form such obscuring features: all such material was certain-
ly removed from the ancient globulars of our Galaxy billions of years ago!
So I am excited to try to understand (and observe!) what effect of resol-
ution, contrast or actual cluster dynamics might cause these "dark lanes".
As usual, the outer areas of M92 displayed a lovely pattern of "arms" or
"streamers" of stars, arcing in patterns fairly symmetrically around the
cluster's intense core. Tonight, thanks maybe to haze, the streamers were
suffused by a haze of unresolved stars even at medium power (220x). As I
raised the power to 285x, I was amazed to see that the core's "dark lane"
not only became more evident, but actually displayed what looked like a
secondary feature: a "tributary" or kink in the darkness split off from
near center and headed East(?), not quite reaching the edge of the core.
At the higher power, though, I also began to notice scatterings of very
faint stars, and tiny, irregular, extremely faint unresolved clumps all
along the length of the main "lane". Still, at no power would I lose the
impression of that cosmic butter knife at work on M92. :)
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