Witch Head Nebula

[Kevnool (Kev)]

Hi peoples , Myself and others have asked about visually viewing the horsehead with good results but heres a extremely difficult one ,The witchhead nebula (IC 2118), Has this object been logged as a visual (not imaged), I tried a few times to no avail out here in the desert but since a couple of days ago on the astronomy picture of the day which has a great(wide field image) of orion ive noticed i was looking to close to Rigel but now i got to wait till summer when its near directly overhead to give this another shot , i,ll be waiting patiently with the 12` and the 16` to try to satisfy my appetite and hopefully see if only the leading edge of IC 2118 ,I`m interested in others opinions....cheers Kev.

[glenc (Glen)]

I have tried without success. Must try again with an image to guide me.

[AlexN]

i've been looking for it the past few nights.... I got nothin... mind you if you two cant spot it in clearer skies with bigger scopes, I guess i shouldn't expect too much..

[ngcles]

Hi Kev,

IC 2118 is a real pain in the you know what to see and I can say that I've only seen it once and it was a threshold detection.

The problem is that in order to see it you need (1) a very dark transparent sky (2) Big Aperture and (3) Wide field -- it is nearly 3 degrees long and a degree wide and there is no way short of hand-held binoculars that you can get that sort of field and they don't have enough aperture.

Item (1) Is no problem to find. If you have (2) then you will almost certainly not have (3) and vice-versa. Large aperture inevitably means long focal length and that means narrow field which means you have no hope of fitting it in.

Your best hope is to abandon the thought of seeing it whole and try to detect a part -- preferably a section or an "edge" between dark (sky) and not quite so dark (nebula).

Your best hope is the boundary on the eastern side (nearest Rigel) at the northern end between the 8th mag star SAO 131759 and the 7th magnitude star at the northern tip SAO 131799. Along here is a definite boundary -- where best (though still not great) contrast is achieved.

A nebula filter is no help -- it is a reflection nebula.

Go for this little zone on a really dark night with a better than ZLM mag 6.3 sky, a 'scope 12" or larger and you widest field eyepiece.

That I think is your best hope.

It was difficult enough under a virtually pristine sky using an 18" in a 58 arc-min field at x85 let me tell you!!

Best of luck,

Best,

Les D
Contributing Editor
AS&T

[Kevnool (Kev)]

Thanks for the reply Les / Alex / Glen the replys give me more inspiration to find these difficult objects and more....as in the thread i mention 12` and 16` these two scopes belong to asnsw Trevor Barry.....so next year as Orion is now to low to observe,so in the summer ahead i,ll report on this object....cheers for now..... Kev

[§AB]

Originally Posted by ngcles

Hi Kev,

IC 2118 is a real pain in the you know what to see and I can say that I've only seen it once and it was a threshold detection.

The problem is that in order to see it you need (1) a very dark transparent sky (2) Big Aperture and (3) Wide field -- it is nearly 3 degrees long and a degree wide and there is no way short of hand-held binoculars that you can get that sort of field and they don't have enough aperture.

Item (1) Is no problem to find. If you have (2) then you will almost certainly not have (3) and vice-versa. Large aperture inevitably means long focal length and that means narrow field which means you have no hope of fitting it in.

Your best hope is to abandon the thought of seeing it whole and try to detect a part -- preferably a section or an "edge" between dark (sky) and not quite so dark (nebula).

Your best hope is the boundary on the eastern side (nearest Rigel) at the northern end between the 8th mag star SAO 131759 and the 7th magnitude star at the northern tip SAO 131799. Along here is a definite boundary -- where best (though still not great) contrast is achieved.

A nebula filter is no help -- it is a reflection nebula.

Go for this little zone on a really dark night with a better than ZLM mag 6.3 sky, a 'scope 12" or larger and you widest field eyepiece.

That I think is your best hope.

It was difficult enough under a virtually pristine sky using an 18" in a 58 arc-min field at x85 let me tell you!!

Best of luck,

Best,

Les D
Contributing Editor
AS&T

Would this object be harder than the Horsehead nebula? Your description certainly suggests so!

[AlexN]

yeah without a doubt..

I've had a brief look at the horsehead region through my 8", whilst i couldnt actually make out the horses head, I knew due to the area where i was looking an in general "what i was looking for" that I was looking at horsehead.. I've been told that using the correct filter (i cant recall at this time if it was a UHC or LPR that someone recommended) I should be able to make out the horses head even with only 8".

Witch head neb can be VERY difficult to find on scopes above 12" which in general (given good conditions, and a DARK sky) shouldn't have much trouble spotting horse head.

[glenc (Glen)]

I have seen the horse head with a 12", but not well, I have not seen the witch head.

[Kevnool (Kev)]

This object is extremely hard to view visually...if you got any hint of light pollution you can nearlly forget about it....but next year i wont rest til i log it

[ngcles]

Hi §AB & All,

Yep, I reckon it is worse than the Horsehead (IC 434 & B 33). It has about the same (perhaps slightly lower) surface brightness as IC 434 but is bigger (much) and it is harder to detect an "edge" between it and sky. This is where having the "head" helps -- it is a truly dark starless intrusion into IC 434 that makes it in turn easier to see IC 434.

The other problem is that there are no filters that are of any practical use because it is a reflection nebula.

I'd be more than happy to accept correction but I doubt it could be seen in less than 30cm, more likely 40cm.

Best,

Les D
Contributing Editor
AS&T

[glenc (Glen)]

Here is an image to guide those attempting to see IC2118:
http://www.astroimages.com/ic2118.htm
It is a refractor image from Astronomical Images by George Greaney.
The bright star is mag 4.8 psi Eri, the galaxy at lower right is mag 13.3 NGC 1752.
The brightest part of the nebula is about 1 degree to the left of psi Eri.

[PhilW]

Originally Posted by ngcles

I'd be more than happy to accept correction but I doubt it could be seen in less than 30cm, more likely 40cm.

I've looked for it without success with 35cm. And yet I've seen the horsehead several times. So perhaps the upper limit of your estimate applies.

Phil

[§AB]

Originally Posted by ngcles

Hi §AB & All,

Yep, I reckon it is worse than the Horsehead (IC 434 & B 33). It has about the same (perhaps slightly lower) surface brightness as IC 434 but is bigger (much) and it is harder to detect an "edge" between it and sky. This is where having the "head" helps -- it is a truly dark starless intrusion into IC 434 that makes it in turn easier to see IC 434.

The other problem is that there are no filters that are of any practical use because it is a reflection nebula.

I'd be more than happy to accept correction but I doubt it could be seen in less than 30cm, more likely 40cm.

Best,

Les D
Contributing Editor
AS&T

Looks like we have a nice challenge here. First one to spot it gets bragging rights

[ngcles]

Hi All,

Just think about this _as a guide_. Back in Glen C's post he had a link for an image of the nebula:

http://www.astroimages.com/ic2118.htm

It appears _on the face of it_ that there was no filters used in capturing the image, so leaving aside the relative sensitivities of the emulsion to different wavelengths (galaxy -v- nebula light), all things are pretty much equal.

At the bottom right-hand corner of the nebula in the photo you can see two very small galaxies. The more obvious one is a spindle elongated in about PA 75. This one is NGC 1752 which (pun intended) is:

NGC 1752 Galaxy *
RA: 05h 02m 09.5 Dec: -08° 14' 26"
Mag: 13.3 (B) S.B.: 13.8 B-V: +0.88 Size: 2.6'x0.8'
Class: SB(r)c: P.A.: 70 Inclination: --- R.V.: ---
Source: RC3 *

This galaxy has a surface brightness (SB) magnitude of 13.8, but you will notice in the photo it is considerably higher in surface brightness than the very brightest parts of IC 2118, true? I'd reckon it is at least 3x, maybe 4x higher in SB than the best and brightest bits of IC 2118.

A little way away at the 8 o'clock position from this NGC galaxy is the tiny round galaxy MCG -1-13-49 that almost appears stellar in the photo -- just a fuzzy dot.

MCG -1-13-49 Galaxy *
RA: 05h 02m 37.6s Dec: -08° 18' 04"
Mag: 15.7 S.B.: --- B-V: --- Size: 1.4'x1.2'
Class: SB(rs)d P.A.: 45 Inclination: --- R.V.: --- Source: RC3 *

There is no published SB magnitude (I'm aware of) but after comparing it with the NGC galaxy and given the MCG integrated magnitude of 15.7, at a guess I'd say it is no better than SB mag 15.5 or possiibly a bit worse. You will see it has about the same surface brightness as the very best bits of the nebula.

So, that puts the surface brightness of the best bits of IC 2118 at _about_ the +15.5 mark --maybe a tad better, maybe a tad worse.

That is what you're up agin.

Now, go and start observing some SB mag 14.0, then 14.5 and then 15.0 galaxies and see how you fare. If you can't see 'em, you're almost certainly gonna be outa luck with IC 2118.

Practice, practice, practice !!!

Best of luck in the hunt !!


Best,
Les D
Contributing Editor
AS&T

[AlexN]

I'll have a look in a few weekends time... going to a star party at a dark sky spot... there'll be a 40cm truss setup there.. my 8" has no chance!

[§AB]

+15.5 SFC brightness, damn, that's low, maybe within reach of a 12" under perfect conditions. I think the optimum mag for this object would be in the 60-80x range, you want a bit of mag to darken the background sky but also maximise your FOV due to the nebula's size.

unfortunately, we'll have to wait several months now to attempt this one.

[glenc (Glen)]

According to LEDA NGC 1752 is V mag 12.4, B mag 13.3, size 3.0'x0.8' position angle 81 and surface brightness 22.5. That is the same surface brightness as NGCs 1313, 2997, 4945, 5128 and 6744. The galaxy 7.9' down to the left of 1752 is PGC 16607 with B mag 14.8 and SB 23.9.

[ngcles]

Hi Glen & All,

Thanks Glen for the info on the two galaxies -- much appreciated (I shouldn't have been lazy and looked further -- but I hate the SIMBAD interface !!!), but ...

The surface brightness magnitudes you have provided from LEDA appear to be in square arc-seconds as opposed to the square arc-mins ones I provided (it came from Megastar) and therefore it _appears_ that there is a disparity in the data. I don't think it is a real (or at least significant) disparity -- basically just different units.

Professional astronomers tend to use the sq seconds measure for surface brightness and amateurs (for one reason or another) seem to use sq-mins (probably because it is used so much in amateur literature -- like Skiff & Lughinbul, NSOG, Megastar etc etc).

But, harking back to my earlier post, I essentially proposed that the brightest and best bits of IC 2118 appear to have _approximately_ the same SB as MCG -1-13-49 (PGC 16607). I also said that NGC 1752 seems to be about 3-4 times brighter than MCG -1-13-49. Therefore the SB of the best bits of the nebula are _about_ 3-4 times fainter than NGC 1752.

Now, disregarding the units for the mean time, it seems from the LEDA data that MCG -1-13-49 (PGC 16607) at S.B mag 23.9 /sq arc-sec is about 1.5 mags (or approx about 3.3 times) fainter in _surface brightness_ than its neighbour NGC 1752 (S.B mag 22.5 /sq arc-sec).

Therefore, proceeding on my proposal that the best bits of IC 2118 are on par with MCG -1-13-49, the nebula is therefore _about_ 3 to 4 times fainter in surface brightness than NGC 1752 -- this is what I guessed earlier and posted -- true?

Please let me know if I've got this wrong!!

A sq arc-sec is 1/3,600th the area of a sq arc-min. A rough rule of thumb I use to convert SB mags in sq arc-sec to sq arc-mins (without mucking around with log tables -- the magnitude scale is a log scale) is to subtract 8.9 from the arc-second figure to get arc-minutes. As near as makes no difference, 2.51^8.9th power = 3600 (well, 3606.6 to be _exact_).

Is the maths right?

Assuming it is, that would (according to the LEDA data) make the SB magnitude of NGC 1752 13.6 mags/sq arc-min, MCG -1-13-49 15.0 mags/sq arc-min and therefore, the best bits of IC 2118 about 15.0 mags /sq arc-min -- right?

(I think I guesstimated 15.5 before)

Either way, IC 2118 is perhaps one of the most challenging visual targets in the entire sky!

Attempts to observe it are very much encouraged from observers with large and medium/large telecopes -- a negative is just as (scientifically) important as a positive -- but you might have to wait till summer again!

Best,

Les D
Contributing Editor
AS&T

[Kevnool (Kev)]

We will have to organize a star party out here when orion is closest to zenith and get some of those big city scopes out here and have a faint object night with prizes to whom ever logs IC 2118 ..........or we all goto Arkaroola......one way or another i will see a trace of it,I,m positive thinking........Cheers..Kev.

[glenc (Glen)]

Les, I just look at the image in Desktop Universe.
Parts of IC 2118 are only just visible in DTU, IC 434 is bright.
http://www.cyanogen.com/products/dtu_main.htm