One of several crustacean-shaped nebulae (crab, prawn, shrimp), Sh2-188 is an old planetary in Cassiopeia. This was one of those ‘cursed’ objects for me, where every time I tried to image it, something would go wrong. I’ve had unforecasted clouds roll in and focuser issues the last two times I tried to dedicate a night to it, so I was glad to find that this time, the gremlins stayed away.The asymmetric shape is hypothesized to be the result of a bow shock interaction with the interstellar medium–see
Wareing, et al 2006. I was gratified to find in that paper they show the same faint structure opposite the bright crescent that I found. Something that took an observatory in 2006, I can now reveal from my backyard. I was also pleased to see that the structure within the crescent is not “sharp.” I thought perhaps there were focus or processing issues in my image, as those filaments look a bit fuzzy or out of focus, but that is how they truly are. Figure 1 in the paper shows the nebula as captured by the 2.5 m Isaac Newton Telescope, which has far greater resolution than my 8″ Newtonian, and you can see that the filaments are indeed a bit chunky, very similar what I revealed in the H-alpha channel. This makes sense given that this is an old planetary that has been expanding for over 20,000 years.
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