Sh2-129 and Ou4 – Imaging the Squid Nebula from Light-Polluted Skies
Is it possible to image faint OIII objects from light-polluted skies like Bortle 8/9 city sky?
This project involved an enormous amount of time (relatively speaking,
considering British weather) spent on narrowband imaging of Ou4 (Squid Nebula)
from my backyard. This data is complemented by LRGB images captured both from my
backyard and from a relatively dark-sky location (Bortle 4). Interestingly, I
was unable to gather any narrowband data from the dark-sky
I dedicated over 60 hours across different attempts to process this image, and
each time the verdict was the same: I need more data. As the target now sets
earlier in the evening and achieving sufficient signal from Ou4 is
This was my first mono imaging project, and Ou4 itself is an exceptionally challenging target. It’s one of the faintest OIII objects of uncertain origin, discovered only about a decade ago in 2011. Taking on such challenges seems to have become a theme for me, given my projects often span over a year.
That said, I firmly believe this target is worth revisiting next year. With better planning, I aim to start imaging earlier in the year, spend more time integrating data in my Bortle 8/9 backyard, and visit dark-sky locations to complement the effort.
To answer the question posed by the title: Yes, it is possible to image faint objects from light-polluted skies. And yes, it’s very hard.
Acquisition
This image combines data from both light-polluted and darker skies:
Backyard (Bortle 8/9):
Narrowband data (Ha, OIII) and LRGB data captured using a ZWO ASI2600MM Pro camera and William Optics RedCat 51 telescope.
Dark-sky site (Bortle 4):
LRGB data captured by collaborator Gleb Deykalo, using a QHY294M Pro camera and William Optics EvoGuide 50ED telescope.
You can explore Gleb's astrophotography on Instagram or AstroBin.
Processing
I processed the LRGB and narrowband data, blending Ha, OIII, and LRGB information to create the final composite.
Gleb gave feedback on the OIII data processing (“Stretch it more!”) and provided an LRGB processing example for inspiration.
About the Targets
Dark Seahorse Nebula (Barnard 150, LDN 1082)
The Dark Seahorse Nebula is a molecular cloud of dust that doesn’t emit or reflect light, but rather blocks it, creating dark spots in the image. Some stars appear in front of the cloud, while others are barely visible, embedded within the dust.
Flying Bat and Squid Nebulae (Sh2-129, Ou4)
Sh2-129, the Flying Bat Nebula, is rendered in both LRGB and Hydrogen Alpha (Ha, 656.3nm), giving it its rich red hue.
Ou4, the Squid Nebula, is a much fainter object, discovered as recently as 2011. It’s rendered in blue-green from Doubly Ionized Oxygen (OIII, 500.7nm). Its faintness makes it a particularly challenging target, even under optimal conditions.
