Re: (IAAC) Obj: M92 - Inst: 17.5" f/4.5 Dobsonian
Very interesting observation Lew thanks for sharing. FWIW it just shows
that you don't need to wait for those pristine skies to go observing.
At 07:33 PM 6/16/99 -0400, you wrote:
>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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