Object of the Week December 16th, 2018 – NGC 1909 (IC 2118) "Witch Head Nebula"

[Uwe Glahn]

NGC 1909 = IC 2118 (LBN 959, Ced 41) "Witch Head Nebula"

Reflection Nebula

RA: 05° 02'
DEC: -07h 54m
Eridanus

Size: ~3°x1°

The history of our OOTW began 1786 when William Herschel noted "strongly suspected nebulosity of very great extent". This astonishing discovery is more impressive when you imaging that Herschel's field in his long focal length 18.7-inch speculum reflector was extremely small. With his normal "sweep - magnification" of 157x he got only 15' field. The IC designation came from Max Wolf who found the nebula on some photographic plates between 1891 and 1905 [1905MNRAS..65..528W].

Physics of the nebula is more complicated than first suspected. The nebula itself is illuminated by the bright star Rigel which lies only around 2.5° SE. It is believed that the nebula is an ancient supernova remnant. Further the nebula seems to belong to the huge Orion-Eridanus bubble which was formed by the Orion OB1 group.

Nevertheless, the nebula seems to be extremely difficult in any kind of telescopes even under very transparent skies. The problem is more the small field or better the huge size of the nebula. Most of the time we only can try to find the edges of the object. I was absolutely surprised when I pointed my small 8x30 binocular to the field and easily saw NGC 1909. Even with my powerful 20x125 binocular the nebula was much more difficult to see. So try out small binoculars and be surprised.

photograph: CEDIC team (Berhard Hubl), Canon EF 200mm f/2.8L @ f/3.5
link to the original side with higher resolution and further info
I2118-4.jpg

sketch: 20x125, 3° field, NELM 6m0+
NGC1909.jpg

And as always,
Give it a go and let us know!

[obrazell]

Interestingly in Harold Corwin's NGC notes he suggests that whatever Herschel saw it was not IC2118 as he saw something East of Rigel not West where IC 2118 is

NGC 1909. WH has one observation of this "Strongly suspected nebulosity of ery great extent." He makes its size "Not less than 2 deg 11 arcmin of PD
and 26 sec of RA in time." These numbers come from his offsets from Rigel: 11m 09s east to 11m 35s east, and 1 deg 19 arcmin north to 52 arcmin south.
While this whole area is covered with a very diffused, very low surface brightness nebulosity, I do not see anything that WH could have seen easily.
In particular, there is no nebula stretched out north to south as WH describes.
However, at about the right distance WEST of Rigel, there is such a nebula, IC 2118. It is bright enough that WH might have seen it during his sweeps,
and it more or less matches his description. So, I am going to suggest, pending visual confirmation, that IC 2118 is the object WH found, and that he
somehow confused "east" and "west" in his log book. That is what I wrote in the 1990s when I went over the field on the first
Palomar Sky Survey prints. However, I now have CH's fair copies of the sweeps available and find that my idea of the nebulosity west of Rigel being WH's
object is impossible. WH observed the nebulosity at least 11 minutes AFTER Rigel had left the field, so NGC 1909 cannot be west of the star. So, there
is no possibility that WH's object is IC 2118.

So what DID WH see? Probably nothing beyond optical (reflections of bright stars, fogging of his eyepiece or mirror, faint clouds or sky glow) or
physiological/psychological (aberrations within his eye, fatigue, hunger, etc) effects.

Owen

[Bertrand Laville]

Hi All,

Very great choice, Uwe !
Here is my drawing (with an enhanced contrast), spent over three nights and a bit more than seven hours at the eyepiece of my 25" dobson Obsession , under good sky of southern Alps (NELM +/-7.0v, SQML 21.8)
http://www.deepsky-drawings.com/ic-2118/dsdlang/fr

Clear skies
Bertrand
http://www.deepsky-drawings.com


IC-2118-T635-BL-2013-02-13-.jpg

[Howard B]

I have one observation from 2007 with my 28-inch scope:

"I could best detect this large and faint nebula by first noticing a long area devoid of stars, so seeing this reflection nebula was easiest as if it were a dark nebula! It was very faintly luminous though, but not by much. 92x" I didn't make a sketch.

Uwe, I love your idea to use small binoculars for this nebula, and I'll give it go next time I get a dark sky this winter.

Lovely sketch Bertrand - and it looks like you also saw a small galaxy through 2118 - is it NGC 1752?

[Bertrand Laville]

Hi Howard,

I saw, without knowing and seeking them, 3 galaxies. See under.

IC 2118 T635 BL 2013 02 13.jpg

[Uwe Glahn]

Very helpful information Owen. In my memory I consider also a mistake in the east/west designation. And after Steve also wrote it in his NGC/IC notes I thought NGC 1909 = IC 2118. Thanks for clarifying this mistake.

Wow Bertrand, what a beautiful sketch. You show that the nebula could also be a target for larger apertures. Thanks for sharing. I definitely try the nebula next time with the 27-inch.

[Steve Gottlieb]

Even though I had read through all of Herschel's sweeps (Caroline's clean version), I'd missed that Rigel was seen earlier in the same sweep. So Owen, thanks for mentioning Corwin's correction.

I haven't spent much time on the Witch Head (I'm rarely observing in excellent skies this time of year), but here's an observation with my inexpensive finder --

Using my 80mm finder at 13x (24mm Panoptic) unfiltered a very large, ill-defined glow (~30'-40') was visible between 1-1.5° south of Beta Eridani. This is the NE section of the Witch Head. With averted vision the glow brightened and stood out fairly well compared to the background sky brightness. This object was significantly fainter than Barnard's Loop but surprisingly was not a marginal observation or as difficult as expected. I couldn't follow the nebula further south with any certainty.

[MelBartels]

Here's my Witch's Head sketch with my little 6 inch f2.8 Jan 2014 turned north up

WH.jpg