It has been already ten years since I imaged the IC5146 Cocoon nebula with the neighboring Barnard 168 dark cloud for the first time. This time my astrophotography setup has a shorter focal length, so the field of view was significantly larger. The frame including a dense star field of the Milky Way contains many of the deep sky object types – including galaxies as well!

The designation IC5146 from the original NGC catalog refers to “a cluster of 9.5 mag stars involved in a bright and dark nebula”. This star open cluster is also known as Collinder 470. It is located about 4,000 light-years away and spans about 15 light-years in space. The cluster central star is as young as 100,000 years only and it is responsible for exciting the local hydrogen cloud to shine in a deep red hue – hence we have an emission nebula. But at the same time, the dust in this area reflects the light of the stars, so we also have a reflection nebula. The emission nebula alone also exists in the Sharpless catalog as Sh2-125, and the whole cluster/emission/reflection complex exists in the Caldwell catalog as Caldwell 19.

Dark cloud Barnard 168 projects westward forming the appearance of a trail behind the Cocoon. A dark nebula is just the same dust cloud as a reflection nebula, and the only difference is the lack of stars in the neighborhood which could light this molecular cloud. So the dark nebula only obscures the stars behind and makes them look redder than in reality – due to selective light scattering. The distance to Barnard 168 is estimated at 500 light-years – so much closer than Cocoon nebula itself.

IC5146 Cocoon with B168
IC5146 Cocoon with B168

High-resolution version here

The data for the image above was collected over several nights in September 2022. Transparency was reasonably good, and that quality is crucial under my suburban sky. Small amounts of haze, high clouds, or smog are enough to significantly brighten the sky background, and that makes classical LRGB color data very difficult to collect. But when the air is clear I am able to spot stars up to 5.0-5.5mag in the zenith, and that is enough to capture color data using a quite sensitive camera such as QHY268M. One trick I do is collecting more data through the red filter, than through the green and blue filters. There are two reasons for that. One is the fact, that most cameras are less sensitive in that part of the visible spectrum, so more data is required to achieve the same level of signal-to-noise ratio in this color – this is regardless of the sky brightness. And the second reason is caused by light pollution which ruins the red part of the light worse, than other colors.

The area which IC5146 Cocoon with its tail Barnard 168 occupies in the sky is a dense star field with a lot of interstellar matter present. But nevertheless, there are still some “windows” where distant galaxies can be spotted. You may check the image below where I selected a few of them. So the list of the deep sky targets in this frame is almost complete now 🙂 We lack maybe a planetary nebula, although I am almost sure it is somewhere there obscured by Milky Way molecular clouds 🙂

Galaxies next to IC5146 Cocoon
Galaxies next to IC5146 Cocoon
Image technical data:

Date: September 2022
Location: Nieborowice, Poland
Telescope: Tecnosky 90/540 Owl triplet
Corrector: TS FF/FR 0.8x
Camera: QHY268M
Mount: EQ6
Guiding: ASI290MM + Evoguide ED50
Exposure: 200:80:60:50 x 2 minutes with LRGB filters
Conditions: Bortle 6, transparency medium-good, seeing medium