Object of the Week May 10th, 2020 – NGC 3184 “The Little Pinwheel”

[Dragan]

NGC3184
UGC5557
PGC30087

Galaxy

Type: SAB(rs)cd

Mag: 9.4
Size: 7.4’ x 6.9’

RA 10h 18m 17.0s
DEC +41° 25’ 27”

Located in the Bears Toes, NGC 3184 is a face on spiral galaxy very reminiscent of M101 – hence the nickname. Discovered in 1784 by William Herschel, NGC 3184 lies a degree east of 3rd magnitude Mu Uma near the southern border of Ursa Major with Leo Minor.

A galaxy abundant with heavy elements, NGC 3184 was home to several supernova over the years. 2 in 1921, 1 in 1937 and another as recent as 1999. Morphologically, NGC 3184 is deemed as an intermediate galaxy lying between the barred and non-barred spirals. It is a barred galaxy but its bar is exceptionally weak and non-descript. NGC 3184 may even possibly be evolving towards a ringed galaxy.

Visually, and as I eluded to earlier, NGC 3184 is similar to M101. A rather large and diffuse object with a somewhat brighter core, its spiral arms tend to be seen best in larger scopes. Minimally detailed observations have been made in scopes as small as 5 inches, but averted vision will still be your best bet to help eek out detail, no matter the scope size. NGC 3180 and 3181 are HII regions located within the east main arm of NGC 3184 but might only be visible in scopes larger than 20” to 25” apertures from dark skies. Lastly, north of center you will find an 11th magnitude star superimposed upon this weeks object.

As always,
“Give it a go and let us know!”

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[wvreeven]

Very nice choice Dragan. I didn't know about the NGC designations of those knots so I will have to revisit this galaxy some time but that may be difficult from Chile. Anyway, when I was ticking off the H400 list, I observed the galaxy and was VERY impressed with the spiral structure. My notes, unfortunately, don't say much more...

[Bertrand Laville]

Hi All,

I observed this face on galaxy some years ago, and I remember that it was a tough target.
I will have a go next week if the weather helps me.

Here is my sketch of 2014 in a good sky (SQML 21.57, NELM +/-6.5) but not exceptional.
The report is here: http://www.deepsky-drawings.com/ngc-3184/dsdlang/fr

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

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[KidOrion]

04/26/19
EAGLE’S RIDGE (junction)
MOON: 23 days (rose at 3:11 AM; 43% illuminated)
SEEING: 7
TRANSPARENCY: 5, gradually a 7 (11 PM onward to 2:30 when we left)
SQM: 21.45
NELM: not checked
WEATHER CONDITIONS: not great, moderate dew; temps in low 50s/upper 40s
OTHERS PRESENT: JO, LR and Donna, RA, DB, DR, FS, AG

All observations: 12.5″f/5 Discovery truss-tube Dobsonian, 14mm ES 82˚ eyepiece (112x, 0.7˚ TFOV) unless otherwise noted

10:11
NGC 3184 (UMa): A large galaxy in the foot of Ursa Major, this one is very diffuse, round, an apparently face-on galaxy with an 11.5-mag star just on the N edge. The galaxy is quite round, 4’ across. It’s diffuse, but also more concentrated along the N-S axis– maybe barred? [It’s not barred, but the spiral arm concentration is strongest on the N-S axis.] The galaxy has a brighter but very diffuse core 0.67’ across, and the occasional glimmer of a nucleus; the nucleus is not an easy hold, and is much more visible in averted, which also greatly helps the overall observation of this galaxy. (The eyepiece might be dirty, which isn’t helping.) The galaxy is not particularly well-defined, especially along the F edge; definition is better on the P edge. 6’ F slightly S from the center of the galaxy is a 13.5-magnitude star. P slightly S by 7’ is a 14th-magnitude star. The brightest in the field is NP the galaxy by 11.5’ and is 6.5 magnitude; 3.75’ N very slightly F that star is an unequal pair with the brighter SF the fainter by 10”; these are 13th and 13.5 magnitudes. 3.75’ S very slightly F the 6.5-magnitude star is an 11.5-magnitude star. P somewhat S of the galaxy by 20’, just on the edge of the field, is a 7.5-magnitude star; this one is flanked to the N and F very very slightly N by bright stars: to the N by 1.75’ is a 9th-magnitude star; to the F very very slightly N by 2.5’ is the brighter of a pair: a 10th-magnitude star with a 14.5-magnitude star P very slightly S by 10”. There’s a wedge-shaped pattern of stars on the P and N edges of the field, and pointing to the SF; this is just outside the field; all the stars in this are between 9th and 12th magnitudes, with the two arms of the wedge separated by 14’ at its tips.

[Ivan Maly]

One of my favorite galaxies. The main features of the structure "jump out at you" in 20" under good conditions (as I had last year), and I first saw the galaxy in my old 4" about 10 years ago. Not long after (2011), I managed a detailed observation in my old 12" SCT, at 230x from the same Bortle-3 site under good conditions. Here is the old digital drawing where I re-drew the original ballpen sketch.

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I also have these notes about the components:

The large, outer NW star cloud is NGC 3180, and the brightest knot in the one SW of the nucleus (more proximally in the same arm) is NGC 3181. Both were described by Lord Rosse and both are attributed to him in HCNGC. It would seem to me that the former feature and the complex nature of NGC 3184 were already described by John Herschel, whose catalog had two entries, 688 and 689, for his father's I.168. Steinicke's book provides an index to some Birr Castle observations of NGC 3184 and h688 but does not treat h689, NGC 3180, or NGC 3181.

[Raul Leon]

Hi here's my observation from 5/4/2019 ; Ngc 3184 is a galaxy in Ursa Major; magnitude:9.8 ; it has a fairly bright halo with a bright central core ; a hint of spiral structure wss observed in times of good seeing. I used a 8mm Ethos at 198x with my 14.5 Starstructure Dob f/4.33876

[Steve Gottlieb]

This observation was made on my birthday, 9 years back!

48" (4/4/11): NGC 3184 is a beautiful face-on spiral with two main long arms and branches, along with several HII knots (two with NGC designations) in the arms. Contains a relatively small, very bright core, ~1' diameter with a sharp stellar nucleus. A mag 15-16 star is visible about 40" NE of the center near the edge of the core.

One spiral arm is attached on the east side of the core and winds counterclockwise around the south side of the core towards the west. The outer halo of the galaxy to the south of this arm has a much lower surface brightness. NGC 3181 is a bright, 15" knot (HII region/massive star cluster) embedded in this arm, 1.2' SW of the nucleus. The arm then continues spiraling outward as it heads north and contains NGC 3180, very small knot with a stellar core at 1.8' NW of the nucleus. This small knot is within a larger, slightly brighter portion of the arm.

A second prominent arm is attached on the west side of the core and rotates counterclockwise around the north side towards the east. The surface brightness lowers on the east side and the arm splits into two branches. A mag 11.7 star is superimposed near the outer edge on the north side beyond the arm.
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Here's the 1856 sketch by R.J. Mitchell with Lord Rosse's 72-inch (published in 1861). I've rotated his sketch so north is roughly to the top. The spiral arms can be easily matched up with the image, as well as the regions NGC 3180 and 3181. NGC 3180 seems more like the tail section of the spiral arm, rather than a specific HII region but without seeing his actual notebook sketches, that's hard to know.

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[Uwe Glahn]

Nice spiral Dragan. Can contribute a very old and not the best sketch with my former 16-inch.

16", 257x, NELM 6m5+
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