Object of the Week Feb 25th 2018 - NGC2174 & 2175 - The Monkey Head Nebula

NGC2174 & NGC2175 - The Monkey Head Nebula and its associated open cluster

NGC2174 & NGC2175 - The Monkey Head Nebula and its associated open cluster

NGC2174/75

Orion

Emission Nebula(NGC2174) & Open Cluster(NGC2175)

NGC2174
IC2159
Sh 2-252

RA 06 09 42
DEC 20 29 00

Size 29' x 27'

Mag 6.8



NGC2175

RA 06 10 53
DEC 20 36 36

Size 5.0'

NGC2174/75 is an emission nebula/open cluster pair in northern Orion. Lying at a distance of nearly 6400 light years near the Gemini & Taurus borders, this pair were first discovered by Italian astronomer and comet hunter Giovanni Batista Hodierna in 1654 and again "rediscovered" in 1857 by German Carl Christian Bruhns.

NGC2174 is a beautiful view in scopes of nearly all sizes but due to it's rather compactness, lower power EP's probably offer the best view. I would suspect that scopes 12" and larger would probably offer the best views. 2174 is about twice as large as the OC 2175 and responds very well to OIII and UHC filters. 2175 can be a bit difficult to detect within the glow of 2174. The nebula is rather bright and apparent in the EP and shouldn't prove too difficult for observers. The nebula also has very nice mottling, streaks and dark lanes throughout lending itself a resemblance to the Lagoon Nebula in Sagittarius. 2175 has also been given the moniker the "Monkey Head Nebula" but for the life of me I just can't see the resemblance. NGC2175, the associated open cluster is a matter of question for me as well. The OC is often neglected in observing reports and gets lost in the nebulosity of 2174. I, for one, do not have any observing notes of 2174/75 where I make a distinct reference to observing the open. My notes primarily focus on the nebula. A quick search online reveals that many other observers fall to the same fate.

Interestingly, there are many cases online where NGC2174 and 2175 are confused for one another. I found so many online sources and observing reports where NGC2174 is referenced as the open cluster and NGC2175 is the nebula. Even an article and image on Sky and Telescope I found incorrectly title 2175 as the nebula. I wonder where the confusion started. Burnhams lists both 2174/75 as the nebula and doesn't even make a reference to the OC. The NGC Project assigns 2174 to the prominent knot within the nebula and 2175 to the nebula as a whole. I'm hoping Steve will chime in to help us clear this confusion. For the purposes of this OOTW, I referenced Simbad as well as Megastar which both identify the nebula as NGC2174. I must admit, I had a difficult time keeping numbers and references straight trying compile some information for this OOTW.


Here is a link to a NASA PDF highlighting pillars within NGC2174 (not unlike the Pillars of Creation in the M16) http://amazingspace.org/uploads/pdf/name/24/lp_ngc_2174_pillars_in_the_monkey_head_nebula.pdf

And as always

Give it a go and let us know!!

http://www.deepskyforum.com/attachme...4&d=1519666357
©HST

Dragan
Harold Corwin has this in his NGC notes about the cluster


NGC 2174 is one of the knots in NGC 2175, which see.
=====
NGC 2175 is a very large roughly circular emission nebula which also includes
NGC 2174 and IC 2159 (both of which see), and a star cluster which has
inherited the NGC number, though there is no mention of it in the discovery
notes. The nebula is centered on SAO 078049, though the brightest knot (which
Bigourdan took for N2175; hence, the "corrected" RA in the IC2 Notes) is
about three arcmin to the west-northwest. Auwers's note makes it clear that
NGC 2175 is much more than just the knot: he gives dimensions of 25 arcmin by
8 arcmin, and specifically adopts the position of Lalande 11668 = SAO 078049
as that for the object. I have followed his lead.
Note that Archinal and Hynes in "Star Clusters" call out another smaller
cluster as "NGC 2175.1". This is a small group of about a dozen stars at
06 10 53, +20 36.6 (J2000) no more than five arcminutes across. They
correctly point out that this has nothing to do with the NGC object -- the
nebula -- and suggest deprecating the NGC number often attached to this group.
I agree, so have not put this object in the main table, but do note that
Collinder 84 is associated with the nebula. Archinal and Hynes have some
doubts that this is a real cluster, but Brian Skiff has it centered on the
same star that Auwers chose. Archinal suggests reserving the NGC number
strictly for the nebula, but if the stars are associated with it, I see no
reason not to adopt the NGC number for Collinder 84 as well. We (observers
over the centuries) have done this with, for example, M 17 = NGC 6618 and M 42
= NGC 1976 with little or no confusion, so doing the same here should not be a
problem -- as long as "NGC 2175.1" is indeed dropped.
=====


I have always liked this nebula and it is often overlooed.

Owen

Here my drawing with a 25" Obsession, through very good sky in Southern Alps:

Attachment 2905

The report of the observation is here: http://www.deepsky-drawings.com/ngc-...635/dsdlang/en

You can have an other observation and sketch, with a 10" LX200 at : http://www.deepsky-drawings.com/ngc-...254/dsdlang/en

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

Corwin doesn't mention the origin and identification of NGC 2174 -- but historically, it doesn't refer to the entire nebula (nor does NGC 2175 refer to the "cluster").

Édouard Stephan discovered NGC 2174 on 6 Feb 1877 using the 31-inch silver-on-glass reflector at the Marseilles Observatory. His description only refers to rather a small patch of nebulosity: "excessive., excess. faible (à peine observable); à l'intérieur d'un triangle formé par trois petites étoiles."

Translated as "excessively, excessively faint (barely observable); inside a triangle formed by three small stars. "

He gives a 1878 position of 06 02 07.47 +20 40 54.4, which precesses to 06 09 24.0 +20 39 53 (2000), and falls on the northwest side of the nebula. This probably needs a small correction in declination based on his reference star, but is still accurate enough to clearly identify a small brighter patch of nebulosity. His three stars are mag 13-14 and the knot of nebulosity is quite prominent on the DSS just following the middle of these three stars. This star has a position of 06 09 21.9 +20 39 30 (2000) and Stephan's knot appears is only 30-40" in diameter, so he missed the entire nebula!!

NGC 2175, on the other hand, clearly refers to the entire nebula as Arthur Auwers described it as "a considerable area of milky, faint light, extended about 8' north-south and 25' east-west. In the brightest part is the 8m star."

None of the 19th century observers made mention of a star cluster.

Hi,
here is my sketch from February 2015, observed with 24"-dobsonian at 80x witt [OIII]-filter
Attachment 2906
Due to my conditions, I can't reach as many details as Bertrand...

Here's my most recent observation and sketch from five years ago with my 28 inch scope:

"This is a large, well-mottled nebula that responds to all my nebula filters, OIII the best. Barely visible without a filter except for a small patch just off the edge of the nebula. Best view at 92x and the OIII filter - this is a lovely sight and one to come back to."

Attachment 2919 Attachment 2920

Oddly, even though I have these notes and sketch I don't remember this observation very well, so now I'm excited for good night to see it again in a couple weeks.

Nice reminder Dragan.

I never revisit this bright nebula since I observed it several times with my former 20x125 binocular. Seems like there are some interesting details within the object.

20x125, no filter, 3° field, NELM 6m5+
Attachment 2925

Hi forum,

Please find attached my sketch of an observation I made last year in January.

NGC 2174:
With my 12-inch Dobsonian at 47x magnification, using an O-III filter, it appeared as an impressively large nebula with various brighter and darker structures with dark bays at the western and eastern sides.

NGC 2175:
A bunch of stars covering a small area. Not really eye-catching, but I was using an O-III filter during the observation, because I was mainly interested in the nebula.
Attachment 2931

Clear skies,

Robin