Object of the Week January 30, 2022 - NGC3198

NGC 3198
UGC5572
PGC 30197
Herschel 146

Galaxy

Constellation: Ursa Major

RA: 10 19 54.9

DEC: +45 33 09

Class: SB(rs)c
Mag: 10.3
Size: 8.6’x3.3’

Give or take 47,292,674.7 light years in the direction of the ‘Bears Toes’ in Ursa Major lies this weeks OOTW. NGC3198 is rather bright, elongated barred spiral visible in a wide range of telescope apertures. One account I found is that NGC3198 was discovered by Lord Rosse Williams Parsons in the mid-19^th century. Another was that it was discovered by Sir William Herschel in 1788. Anyone?

Scientifically, NGC3198 has played a pivotal role in our understanding in the universe. In one paper published in 1999, researchers used the Wide Field and Planetary Camera 2 (WFPC2) on Hubble to locate and measure the distance to 52 different Cepheid Variables located in NGC3198. Using this data, astronomers were able to ascertain a rather accurate distance to our OOTW of 14.5±1.2 Mpc – giving us the number I sarcastically opened this post with. NGC3198’s distance is so well measured that is used as a ‘calibration’ galaxy for the Key Project. In short, the Key Project was a study using data obtained through Cepheid observations in ~25 ‘nearby’ (~65Mly) spiral galaxies from the HST to help measure and refine the Hubble Constant – one of the principle goals for which the HST was designed and built. These refined distances of nearby galaxies would then help to refine observations and distances to galaxies further away (65Mly to more than 325Mly distance). NGC3198 is now used to help refine these other observations.

Another interesting bit I learned about NGC3198 is that it’s considered the “flagship” galaxy for evidence of dark matter in galaxies. In a 2015 paper titled The dark matter distribution in the spiral NGC 3198 out to 0.22Rvir alludes to the amount of dark matter measured in NGC3198 may actually be at least 4 times larger than the amount of visible matter. NGC3198 is MUCH larger than it appears to the eye.

To an eye looking through a telescope, NGC3198 makes for a fine sight. Telescopes in the 10” range provide the observer with a rather large, faint smudge with the possibility of spotting some mottling. In scopes approached 18” to 20” from a dark sky, the galaxy appears elongated on a NE to SW position angle with a bright core and the makings of spirality.

So if you’re out late this dark moon or next, please point your scope towards the Great Bears Paws. I think you’ll be pleasantly surprised at this galaxy. Not just for its appearance in the eyepiece, but for its overall contributions to the advancement of our understanding of this awesome universe!

And as always,
Give it a go and let us know! Good luck and great viewing!

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©Adam Block

"Difficult to see from Chile this galaxy is!" Luckily I observed it from SQM 21.4 skies in central Spain in March 2015 using my 20" dob. I didn't notice that is was a barred galaxy though:

At 320x this galaxy is an elongated glow with a reasonably bright central region. It takes an S-shape because of two spiral arms. The south-eastern arm is split in two and this is very difficult to see.

Three observations in my log, the most recent one almost 11 years ago. 12" SCT @179x / 27' under less than optimal Dutch skies, but the fact that I was able to make out a bit of detail, as described below, is testimony to the detail this galaxy is willing to reveal:

A NE-SW elongated, faint streak, slightly brighter in the center, a relatively large, brighter core. Using AV the core is larger and brightens notably, very faintly shows slightly ragged structure. Directly NNE and twice that distance towards the NNW are mag. 11 stars, half the distance of the NNE mag. 11 star, towards the south, is a mag. 13 star.

The other two observations in my log were in an 8" SCT, both in spring 2007. Back then, in the smaller aperture I was unable to make out much more than a central brightening, confirming Dragan's note that a scope in the 10" range may be required to start making out fainter details.

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Click here to download this observing guide.

I am sure Steve will chip in but Wolfgang has William Herschel discovering it on the 15th Jan 1788. I can check his massive tome on this for further information.

Got two observation on NGC 3198 as a part of the "Rosse Spirals".

In the last observation with 14.5" and 283x I wrote: large, around 5' long NE-SW elongated galaxy; bright with estimated tightly spiral arms; easiest spiral started 1' SW of the core and turns NE without connecting the core, quickly disappearing; another spiral arm starts 1' NE without any winding, only visible as a longish brightening; from the long axis two dark structures rises into the galaxy without showing a clear spiral structure

sketch: 14.5", 283x, NELM 6m5+, Seeing II
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Quote:

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Originally Posted by obrazell

I am sure Steve will chip in but Wolfgang has William Herschel discovering it on the 15th Jan 1788. I can check his massive tome on this for further information.

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Yeah. I assumed Herschel was the rightful discoverer, especially with the designation "Herschel 146". But Rosse also was listed as a discoverer so I was a bit uncertain.

Through Jimi's 48" in early May 2016, observing also with Howard Banich:

NGC 3198 is a showpiece, large spiral extending SW-NE, ~8.0'x2.5'. Contains a bright, elongated central "bar", punctuated by a very small bright core that rises to a stellar nucleus. Slightly brighter patches are visible at the ends of the central region, where the spiral arms emerge. A tight inner arm is attached on the northeast end; it bends back sharply and closely parallels the central region, extending southwest for a length of ~3.5'. An outer low surface brightness arm sweeps clockwise on the southwest end. A symmetric outer arm on the northeast end (of slightly higher surface brightness) curls clockwise towards the west. The outer tip to tip diameter is nearly 8'. An uncatalogued fairly bright double star [separation ~3.7"] is 3.5' NNE of center, just beyond the halo and a mag 14 star is 2.2' SSE of center.

Here is a copy of Caroline's handwritten notes with NGC 3198 boxed and my translation:

"considerably bright, much elongated, about 5' long and 2' broad, very gradually brighter in the middle, from south-preceding to north-following. 15 Leo Minor follows by 32 min 1 sec, south by 0° 24'."

The "1860" in parenthesis has nothing to do with a date, but refers to his discovery number.

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Following on Steve's observation above, here are my notes and sketch of 3198 from May 4, 2016 with Jimi's 48-inch:

"A nearly edge-on barred spiral, the double spiral arm stands out quite well. The central bar is greatly fore shortened, but appears brightest on each end. 375x, 21.76 SQM."

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Hi, here's my observation from 1/31/2022: Ngc 3198 galaxy in Ursa Major ; mag:10.27 ; size: 6.5' x 1.8' ; fairly bright, elongated with bright core and mottled arms; I used a 14mm Meade Ultra wide eyepiece at 153x with my 14.5 Starstructure f/4.3Attachment 4602

My observation with my 20" from March 13, 2015 from mid-Spain:

At 320x a large galaxy with a reasonably bright central region. It takes an S-shape because of two spiral arms. The southeastern arm is split in two but this is barely discernible.