NGC 3938 (LRGB) (rhedden)

NGC 3938 (LRGB)

NGC 3938 is an 11th magnitude SA(s)c spiral galaxy in Ursa Major, measuring 5.4' x 4.9'. Discovered in 1785, it is on the original Herschel 400 list. Distance estimates range from 43 million to 58 million light years. (Source: Rick Johnson, Mantrapskies.com).

This image is an LRGB image taken from my Bortle 4/5 backyard, with RGB data from 2020 and L data from 2021. I took very long, oversampled RGB subs (18 minutes) to see if I could get a little bit better resolution on the H-alpha regions. The answer is "no." The seeing was below average when I took the luminance subs, but there is not much I can do when I get so few clear nights in the late winter. About 2/3 of the luminance subs were taken with the 35% illuminated moon on the other side of the sky, so I have marked Bortle 5 in the acquisition details.

Processing notes: I usually don't crop my galaxy images much, but there is an obnoxiously bright star just outside the field of view, which I found distracting. It reminds me of my inconsiderate neighbor's motion-activated spotlight. I'm trying to image a galaxy, and here's this bright distraction shining on my gear. Let's crop out the bright star (and the neighbor).

Modest noise reduction was applied using Noiseware, and a bit of smoothing of the background in Images Plus. Since I was combining data with two different camera rotations, I ran into all kinds of strange problems with fixed pattern noise when I attempted to add the RGB subs to a synthetic luminance stack. I abandoned that approach and just used pure luminance subs in the end. Remind me to never take data on a project in two different years. New flats, different rotation, different seeing conditions, etc. conspire to make processing much more difficult.

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Status	Basic success
Started	...
Astrometry.net job	4330029
PixInsight job	n/a
PixInsight queue size	n/a
PixInsight stage	n/a

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