File:Butterfly nebula.jpg

English: sh2-108 is often called the Gamma Cygni (Sadr) nebula or even Sadr region because of the foreground appearance of the supergiant star. However, this is an optical illusion: this nebula lies far beyond Gamma Cygni/Sadr in the depths of the Cygnus X complex of star formation regions. Sadr itself lies at a distance of ~1500 light years.

The small open cluster of stars above Sadr in the top middle is NGC6910. This cluster however may be located within the nebula itself, as it is at a similar distance of ~3700 light years beyond the galactic Great Rift (the dark band of interstellar clouds of cosmic dust obscuring the middle of the Milky Way, including the stellar association Cygnus OB9, whose core cluster comprises NGC6910). Apparently the dust in front dims the light from the open cluster by more than one magnitude. Still, this 2.2 magnitude object resembling a butterfly shape (and is sometimes also called that) shows off a number of both emission and dark nebulae.

This is my first image after a long hiatus, since 2022 was very busy for me. Thankfully, sh2-108 was a relatively straight-forward target, very bright even though I put in some good time on it which helps with noise control and also weighting of images. Even though I've been busy with sciencing the past summer, the weather was not cooperative: there was lot of rain and clouds and the seeing was terrible. So having a lot of exposures helps with improving quality. I avoided doing this target in the past because there's a much larger context that is beautiful and maybe best done with a wide field lens or as a composite but given my time availability, I chose to do the path of least resistance here.

The first image (A) is a Ha only image (https://www.astrobin.com/nm6fwk). The second (B) is the PixInsight processed image, quite minimal, using the Ha for the L image. I tried a composite L from the mono S2, Ha, and O3 data but Sadr really showed up brightly (due to the O3 signal) and decided this was the better route. I also further processed the PixInsight image in TopazStudio 2 (C - minimal and D). As usual, the processing in C and D looks aesthetically great from far away but if you zoom in, you can see the compromises made to achieve the better look.