Object of the Week, September 6, 2020 - IC 5146 - The Cocoon Nebula

[Uwe Glahn]

IC 5146 = LBN 424 = Sh 2-125
Cons: Cygnus
RA: 21 53 29
Dec: +47 16 01
Size: 12'

The history of our OOTW started 1893/1894 when Max Wolf and E.E. Barnard discovered this nebula independently on a photo plate (a 6" lens each). Our expert contributor Steve G. brings more light in the history in a thread here in 2015.

The "special feature" here is its galactic position within a massive molecular cloud. The strong star formation makes the nebula not unique but interesting for visual observer. That means we can observe a central Open Star Cluster (Cr 470) surrounded by a nebula (Cocoon) which shows signs of emission, refection and absorption. As a nice addition, especially for smaller aperture we find the large Dark Nebula Barnard 168

Physically the distance of the whole complex is around 3000ly away. High resolution spectral analyses let the nebula classify in a crossover stadium between a reflection and emission case. The central star cluster consists of around 100 young stars up to 12mag.

Most easiest detail in telescopes or even smaller binoculars is the long dark structure B 168 which can be seen as a thin, nearly 2° long streak. The Cocoon is much more difficult and even mid size telescopes can have trouble with it when the sky is not transparent enough. Best filters are UHC and Hß.

photo of IC 5146 + B 168 by Fabian Neyer (larger)
cocoon.jpg

sketch of IC 5146: 27", 113x, Hß, NELM 6m5+
IC5146.jpg

As always, give it a go and let us know.

[Raul Leon]

Hi here's my observation from Chiefland Florida 10/5/2010; Ic 5146 aka the Cocoon nebula in Cygnus ; magnitude:7.2 ; size:12' ; large and low surface brightness, this nebula really pops out when a H beta filter is used. Roundish with some stars superimposed. I used a 22mm Panoptic at 75x with my 14.5 Starstructure Dob f /4.3 ic 5146.jpg

[j.gardavsky]

Hello Uwe,

and thank you for choosing this nebula.

For whatever reason ever, I have just 1 entry in the observing logbook: 3rd November, 2013:
Achro refractor 6" F/5, eyepiece Swarovski 22x (f=21mm, AFOV 59°), filters H-Beta, and blue(RGB)CCD: fairly bright "cotton" ball, no structures

When viewing the nebulae with the mix of emission and reflected light, the Baader blue(RGB)CCD (bandpass 400nm - 510nm) is often an alternative to the narrow passband filters, like H-Beta and OIII.

On a side line, this Cocoon Sh2-125 is the 3rd nebula nicknamed as Cocoon or Little Cocoon: Sh2-82, Sh2-124. All of them visible through the 6" F/5 refractor.

Clear skies,
Jiri

[lamperti]

From 2013 with a 22" at 337: "A small faint glow seen without a filter. The UHC filter helped. Looked like a small planetary. No sharp edges."

[Ivan Maly]

I observed this in January 2012 with my old 12" SCT and 55-mm ocular. "Roundish nebulosity with a pair of bright stars, surrounded by a ring of darkening. A brighter and wider pair at the edge of the field beyond the dark ring. Nebulosity looks rather like a distant, mostly unresolved open cluster, there are a few distinguishable stars besides the bright ones. H-beta leaves only one of these fainter stars and makes the nebulosity stand out better." It was a particularly cold, transparent night.

[Steve Gottlieb]

My first observation was in 1983 with an 8". This one is from 1991 with a 17.5".

At 82x using an H-Beta filter, the Cocoon Nebula appears fairly bright, very large, about 10' diameter. Surrounds six stars including two bright mag 9-10 stars embedded near the center and at the south edge. Has an irregular round shape with a very irregular surface brightness with dark mottling and brighter regions. The nebula is quite prominent using an H-Beta filter, which gives an excellent contrast gain (higher than OIII). The nebulous glow is superimposed on a scattered star group and is situated at the east end of long dark lane (Barnard 168) that extends 1° WNW! (excellent in binoculars). There is a distinctive edge to the Milky Way on the north edge of the lane.

[Dan Smiley]

So far I have only a negative observation from 2018 using a 13.1” dob. While the dark lane was clearly visible, the unfiltered view trailed into a starry field with no sign of nebulosity. I am waiting for arrival of an h beta filter as well as departure of smoky skies to try again soon...

[tadas]

Hi all,

I had an opportunity to observe this week and did look at IC 5146. I noted that in my 14" telescope it was "A faint glow enveloping several fairly bright stars. While overall shape is round, the outline at the same time seems somewhat angular. No internal structure observed. UHC and OIII filters did help a bit, but not much. Very rich and interesting field".