Object Of The Week October 24, 2021 - IC 1396 and the Elephant's Trunk

[wvreeven]

IC 1396

Emission Nebula

Cepheus

RA: 21 39 00.0
DEC: +57 29 24

Diam: 170' x 140'

IC 1396 was discovered photographically by E.E. Barnard in August 1893 using the 6" Cook refractor at Vanderbilt Observatory. The discovery was published in "Photographic Nebulosities and Star Clusters connected with the Milky Way". That, unfortunately, is all information I could find on the internet.

Simbad, oddly, classifies the object principally as an open cluster with a note indicating "Cl+Neb HII". The cluster also bears the designation Trumpler 37. A part of IC 1396 is known as the Elephant's Trunk nebula. Many people therefore call the entire nebula by that name, but strictly speaking this is incorrect. Wolfgang Steinicke lists this part of the nebula as IC 1396 A and Simbad redirects to The Elephant Trunk molecular cloud when queried for that designation. IC 1396 A also bears the designation Sh2-131 and in it lies the YSO (Young Stellar Object) vdB 142, which can be seen as a small reflection nebula. Several dark clouds in (front of) the nebula bear Barnard designations. Here is a map of the region:

Screenshot 2021-10-25 at 11.06.46.jpg

The nebula lies some 2400 lightyears from Earth. The name Elephant's Trunk arises from the visual appearance of the dark nebula IC 1396 A, which seems to resemble the head and trunk of an elephant. The bright star HD 206267 illuminates and ionizes the entire nebula and the rims of the dark globules therein, including the Elephant's Trunk nebula, protect the dust inside the globules from the ultraviolet radiation of that star. In 2003 several very young (~100,000 years old) stars were discovered in IC 1396 A on infrared images. Two slightly older (~ few million years old) stars lie in the head of the globule and their stellar winds may have pushed away the dust there. The combination of the ultraviolet light of HD 206267 and the stellar winds of the two slightly older stars may have triggered the star formation in the globule.

Visually the nebula is a challenge due to its low surface brightness. Many starting observers indicate that they tried to observe the nebula without success. First of all, it is HUGE. Secondly, it isn't very bright. Dark skies and preferably nebula filters are needed to give this nebula a try.

I have one logged observation of the nebula from SQM 21.4 skies in central Spain in August 2016. I make no mention of the cluster nor of the YSO so I should revisit the region some day.

"At 83x very faintly visible without a filter. UHC makes it visible very well. Several dark nebulae are seen in and around it, especially B 161. The brighter edges of the nebula of the Elephant's Trunk are not visible, but I do see the dark lane inside it."

As always,

"Give it a go and let us know!
Good luck and great viewing!"

[lamperti]

I have attempted this object 5 times over the many years. At first, as a newbie, I did not see any nebulosity with a 10". Nine years later with a pair of binoculars: "O-III in front of binocular shows some nebulosity. It is large like the North American nebula." Using a 22" at 77x and either a UHC or O-III filter, "Both filters show about the same. Can see milkiness and nebulosity extending across the whole field. Quite a few stars embedded in it. Roaming around, there are places where there are no stars or nebulosity."

On another occasion, with a 20" at 73x looking for B-161, "Within IC-1396. Very obvious blank area. Maybe a half dozen stars within it but dead center is very dark. Opacity = 5/6"

[Uwe Glahn]

Two tough objects Wouter. I run a lot of attempts and got negative results most of the time, because of wrong or missing filter or simply to small fields.

I finally had success with my new widefield ATM binocular, which gives me around 5° nicely illuminated field and allows normal 2-inch filtering. But the object remains faint. The difficulty was to separate nebula background and dense star fields.

sketch: 4" binocular, 14x, Hß filter, NELM 6m5+
IC1396.jpg
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Very the same experiences with IC 1396A. The first tries with the 27-inch were sobered. Nearly nothing to see, beside very faint edges. But the object needs time and the right transparency. I finally used a UHC filter and mid size EP.

sketch: 27", 113x-172x, UHC, NELM 6m5+
IC1396A.jpg
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[j.gardavsky]

Hello all,

over the last 20 years, I have 141 "having seen" entries on this IC 1396 (Sh2-131) nebula in my observing logbook through the binoculars 7x35 up to 25x100, and all nebular filters I used to have. And I have also seen it with unaided eyes.

The visual appearance has been like three-parts, the southern rim has shown the B 160 dark nebula (nicknamed the "Frog"), other dark nebulae less certain. The Elephant Trunk insert not resolved through the binoculars.

This nebula is the brightest member in the Cepheus Bubble https://www.researchgate.net/publica...Cepheus_Bubble
http://deepskyview.de/2018/11/cepheu...er-wide-field/

and nearly most of the visual objects in the Cepheus Bubble are within the reach of the binoculars, and especially through the H-Beta filters.

Clear skies,
Jiri