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View Full Version : Object of the Week, March 29, 2020 – NGC 3738 / Arp 234



Howard B
March 30th, 2020, 01:17 AM
Irregular / starburst galaxy
Ursa Major
RA: 11 35 47
DEC: +54 31 32
Magnitude: 12.04 (v)
Size: 2.5’ x 1.9’

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Following the dictates of staying home to help slow the spread of COVID-19, I observed from my back yard last weekend. The weather was exceptionally nice and the night skies were pretty darn good too – better than I imagined in fact. Over two nights I was able to see six Arp peculiar galaxies through my suburban/rural skies with my 28-inch f/4 scope, and one in particular grabbed me, Arp 234 - aka NGC 3738. I liked it enough that I thought it would be a good OOTW while I was observing it, so here we go.

NASA has a nice summary of 3738 at https://www.nasa.gov/mission_pages/hubble/science/ngc3738.html so I won’t cover the same territory - I'll concentrate on how this irregular, starburst galaxy looked in the eyepiece. Located just outside the southern border of the Big Dipper’s bowl, a few degrees west of Phekda, 3738 is an easy star hop, and at magnitude 12.04 it’s bright enough to easily see in scopes much smaller than I was using.

It’s also a fairly good size at 2.5’ x 1.9’, so even under less than ideal skies, this galaxy should be within reach of most amateur telescopes. Here’s what I saw:

“This is cool – I can see the brightest knot at the western end of this smudgy galaxy. The faint star (mag 14.5) just off the western knot is visible with determined averted vision, as is an even fainter star to its north (mag 15). All this takes magnification well and looks best at 547x. 20.30 SQM.”

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The galaxy looked nice at 253x and 408x as well, with the brightest knot becoming more distinct as the power increased. If the seeing had been steadier I’ll bet it would have looked even more detailed at 700x, and under a darker sky perhaps another star forming knot or two would have become visible.

As a bonus, following a short string of 10th and 11th magnitude stars a half degree to the south will bring you the magnitude 10.9 spiral galaxy NGC 3756, so pop down for a quick peak while you’re in the neighborhood.

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

(ps - my sketches were flipped so north is to the left - the HST image is north up.)

Raul Leon
March 30th, 2020, 02:31 AM
Hi here's my observation from 1/12/2013: Ngc 3738 and Ngc 3756; both galaxies in Ursa Major; magnitude: 11.3 and 11.42 ; ngc 3738 is an irregular galaxy that seems to have a bright HII knot ( at top of sketch) and ngc 3756 is a spiral galaxy (bottom of sketch), both galaxies are in same field of view. I used a 14mm Meade Ultrawide eyepiece at 113x magnification. 3826

Uwe Glahn
March 31st, 2020, 06:09 PM
Nice Arp-Galaxy Howard and a good motivation to observe during the time of quarantine.

One interesting detail is that you also saw a comet shaped body like me. No photo shows that overall form. I described it as a "bean" shape starting from the brightest knot. When I observed the galaxy under better conditions you had I was fighting to resolve the brightest knot itself. I got 3-4 peaks within the brightest knot. Further following I could pick up some more brighter regions. All in all a very interesting and challenging galaxy.

sketch: 27", 586x-788x, Seeing II-III, NELM 6m5+
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Ivan Maly
April 2nd, 2020, 09:12 PM
"Gives an appearance of a small and fat M104 with the main mass on NE side." That's my notes from four years ago (SQM 21.64, 12", 250x). North in the HST image above is approx. 70 deg CCW from top.

Steve Gottlieb
April 5th, 2020, 03:26 PM
These notes through my 24-inch were not under the best conditions -- mushy seeing restricted my power to only 200x and I realized later that the secondary was partially dewed. SQM was probably about 21.4.

24" (5/27/17): at 200x; bright, large, elongated 3:2 NNW-SSE, ~2.0'x1.3', noticeably mottled or knotty appearance. Broad concentration but no defined core or nucleus. A brighter knot (HII complex?) is on the northwest side. A chain of bright stars begins at a mag 10.5 star 2.5' NE of center and extends southeast. NGC 3756 is 16' SE.

morsie
May 1st, 2020, 10:56 PM
My Notes from when I owned a 24" f.4.5. I now have an Obsession 22" UC and will revisit.

Nice medium size and bright oval elongated 1 1/2 to 1 with a brighter extended bulging core. The core is very large in proportion to the rest of the visible area. Averted shows more size with mottling and structure. Nice pair of 11th mag stars 3min and 5min E respectively. PA = 135. ARP 234