Casitas de Gila, Gila, New Mexico
March 31, April 1 - 5, 2022

Reprocessed 2/6/2023

I made my Spring trip to a dark sky site in New Mexico with galaxy season in all its glory (Spring break from the clouds and rain in Oregon).  For all imaging, I used my Celestron 9.25” SCT at prime focus (FL = 2350mm, f/10).  There were so many galaxies to pick from, and to take advantage of the fairly long nights, I imaged three targets each night primarily waiting for Virgo and Coma Berenices to get to optimal positions in the sky.  NGC 3184 was the first target where I captured between two and three hours of data over several nights using Luminance, Red, Green, and Blue filters.  For the first time, I captured luminance data with 4 minute exposures instead of my customary 2 minutes.  Only the brightest stars were clipped, but the galaxy core details were preserved.

Original Version:

While atmospheric conditions were predicted to be average or better, there was enough variation in transparency, seeing and sometimes wind, that guiding and subframe quality were below my expectations.  I had not used the telescope without a focal reducer for almost a year and I had become used to improved guiding in PHD2 using the multi-star guide option.  It was also difficult to find more than one guide star around the galaxy.  Guiding performance varied from 0.6 to 0.95 arc-min.  Also, the temperature dropped between 30 and 40 degrees Fahrenheit, so the auto focus routine ran often and had difficulties with so few stars in the field of view.  Another learning was that strong winds during the day battering my Telegizmo 365 cover moved the mount and hardware by about 1 to 2 arc minutes, so I used the Polemaster camera with SharpCap Pro V4 each evening to fine tune the polar alignment.  Other astrophotographers and I also suffered from several AC power outages, one human caused and the others from a prickly GFCI.

I continued to have success with the NormalizeScaleGradient script applied to the aligned subframes.  I tried and tried to create starless images of the luminance and RGB color images in the linear state with StarXTerminator (AI version 10) and StarNet2 in PixInsight.  StarXTerminator removed part of the galaxy core while StarNet2 left too many artifacts.  For NGC 3184, I had to stretch the image first, then apply StarXTerminator.  I then finished stretching the starless and stars images before combining into a LRGB image.  Both tools still have issues with galaxies, especially in the core region.  Stretching images was done with different tools using a try and apply approach.  A combination of GenerisedHyperbolicStretch, HistogramTransformation and CurvesTransformation were employed in a non-reproducible way.

Reprocessed 2023:

I continued my effort to reprocess most of the image data sets that had serious flaws and issues using new PixInsight tools and an improved workflow.  NGC 3184 lacked detail in the galaxy structure.  Again, Russ Croman’s XTerminator tools made a significant difference in improving the imaging and simplifying the workflow.  In this case, StarXTerminator was applied to luminance and RGB color images after they were stretched.  Otherwise, the galaxy core was extracted with the stars.  A few halos and artifacts caused by the very bright star were removed in the starless images using Photoshop,  The colors and saturation required more adjustments than normal for me using color masks and the CurvesTransformation tool. 

Description:

NGC 3184, the Little Pinwheel, is a face on spiral galaxy in Ursa Major.  It has a small nucleus and long sprawling spiral arms. Although it contains hundreds of billions of stars, the blue color of its spiral arms comes mostly from a relatively few bright young blue stars.  NGC 3184 is a type SABc spiral, it is about 38 Mly from Earth, and it has a diameter of about 81.6 kly (NASA and SkySafari Pro).  There is a very distant galaxy to the right of NGC 3184, PGC 2181848, a 17th magnitude spiral galaxy estimated to be 1260 to 1400 Mly away, 164 kly across and is moving away from us at about 9.6% of the speed of light.

Imaging details:

Celestron 9.25" Edge HD SCT (FL = 2350mm, f/10)
Celestron off-axis guider with a ZWO ASI 174MM mini guide camera
Losmandy G11 mount with Gemini 2
ZWO ASI 2600MM Pro cooled monochrome camera (-10C)
ZWO 36mm Luminance, Red, Green, and Blue filters
Equatorial camera rotation: 340 degrees

Software:    Sequence Generator Pro, ASTAP plate solving, PHD2 guiding, 
    Losmandy Gemini ASCOM mount control and web client interface,
    SharpCap Pro for polar alignment with the Polemaster camera,
    PixInsight 1.8.9-1 with Russ Croman’s XTerminator tools,
    Photoshop CC 2022/2023

Luminance    4 min x 56 subframes (224 min), Gain 100, Offset 68, 1x1 binning
Red     4 min x 28 subframes (112 min), Gain 100, Offset 68, 1x1 binning
Green    4 min x 27 subframes (108 min), Gain 100, Offset 68, 1x1 binning
Blue    4 min x 25 subframes (100 min), Gain 100, Offset 68, 1x1 binning

Total integration time: 9.1 hours