One may be forgiven when observing N186 for logging it as a not-altogether sensational view…  merely a small and serene scene consisting of a small cluster of stars (NGC 1791), an even smaller cluster of stars (BSDL 384), and a few exceedingly faint wisps of nebulosity, all set against a beautiful backdrop rich in stars. But in reality, like all superbubbles, this is far from a serene scene… it’s a maelstrom where the ferocious winds and supernova shock waves of massive stars are carving out a huge cavity (325 light years in diameter) in the surrounding gas.

Unlike the showpiece superbubbles such as the jaw-droppingly beautiful N11 and N44 – both chock-a-block with stupendously bright and complex nebulae and beautiful clouds of stars – modest N186’s handful of stars and threadbare nebulosity is nonetheless a worthwhile observation on which to spend some time because it is a rare treat not only to see what has happened in the last few million years (albeit you can’t really see a whole hell of a lot), but also consider what is going to happen – there are plenty more hefty stars inside N186, and over the next few million years they will pop off like firecrackers, their debris expanding outwards fast enough to eventually catch up with and slam into the bubble’s edge. Then we’ll have something sensational to see!

This superbubble certainly requires a very dark and transparent sky, good dark adaptation, and lots of averted vision in order to catch much of anything. And time. It is one of those objects that you really need to spend some time with if you want to tease out strands of nebulosity from this incredibly faint and threadbare superbubble.

A very pretty superbubble, but alas, very little to be seen in our telescopes. Credit: NOAO/CTIO/MCELS

16″ at 228x: NGC 1791 appears fairly bright, irregular in shape, ~45′ in diameter. Its centre is speckled with a few mag 14-15 stars dotting the glow of unresolved stars, and a mag 14 star lies on its northwestern edge. With the UHC filter, NGC 1791 appears embedded in a very short ghost of a streak of nebulosity that runs in a NE-SW direction; it looks like an Impressionist’s softest brush stroke of faintest pearl-coloured light, a wraith-like tendril so pale that it is almost translucent against the rich starry background.

While using the UHC filter, I used averted vision to see what else I could see of the superbubble. I think that I caught the most fleeting glimpse of another smudge of nebulosity on the southern edge of the bubble, but it was extremely faint and extremely small – nothing more than an almost-transparent strand of threshold nebulosity that quivered into view but melted just as quickly back into the background; one of those once-off views that is so fleeting, one is not sure if it can be logged as seen or not. Probably not.

16″ at 228x: BSDL 384 appears as a mag 11.5 star buried in a very small, and very faint glow of unresolved starlight. The star R67 =HD 32763, is a cool one to observe as it is a red supergiant.

It is unclear whether SNR N186D, lying on the superbubble’s northern edge is physically connected to the superbubble or whether this is a chance projection of separate objects along a line of sight. Either way, it remained steadfastly invisible to my telescope at low magnification, with and without an OIII filter, and the only way I knew where I should be searching was thanks to the mag 13.4 star LHA 120-S 152 (OB-type).

16″ at  228x: This was a pleasant little surprise – a very small, round, very faint droplet of nebulosity floating amongst the host of background stars.