M101 – Pinwheel Galaxy (LRGB)

M101 (LRGB, Zoomed)
M101 (LRGB)


This is M101, better known under the name “Pinwheel Galaxy”. It is a relatively large face-on spiral galaxy in the constellation of Ursa Major. A very untypical summer target, but I still decided to take my archnemesis on again. M101 is approximately 29 million light years away from Earth but still manages to have a large apparent size of around 29’×27′. The galaxy features very large extending spiral arms which can be barely seen.

This galaxy is a typical Sc type galaxy, featuring a large circular symmetry and a very bright central nucleus with a spiral structure. Typical for Sc galaxies are multiple visible spiral arms, which can definitely be seen in this image of the Pinwheel itself. This galaxy also features a multitude of HII regions in the spirals, which I sadly did not manage to properly capture. They would have shown up in a relatively bright red hue along the spiral arms. Those regions are, like our HII regions, where stars are born.

What I am actually proud of is that, when you look very closely in the nucleus, you are able to make out faint structural details even in the very core of M101. The next time I’ll try to capture this galaxy is earliest next winter, with a larger scope that should feature even more details of this beautiful galaxy.

Technical Details

Okay, so, I apparently somewhat managed to recollimate my Newton again to a decent degree. The results weren’t that bad this time after all. I had to anyway because I got a new focuser for the device and actually managed to attach it properly. Very good thing, that new focuser. Collimation is still not on point. Who would have thought. Might need to do some modifications on my secondary mirror to finally get rid of the issues once and for all.

I am very pleased with the detail in the galaxy itself, it turned out much better than the M101 I shot before. I tried to merge both data sets but to no avail, the older data was just not good and blurry. It basically ruined my whole integration.

Speaking of integration, for the first time I actually managed to do a CFA drizzle on my RGB data (which was super shit with lots of raining noise). It made processing everything a bit easier, even if not super good. I found out the issue, and it was the dithering was only in RA. I changed it to spiral mode with very good results (captured my next image already). For some reasons my DSLR flats don’t properly take. I need to figure out why.

Acquisition Details

Shot with Atik 383L+ on SkyWatcher 8″ f/5 PDS and Nikon D5100 on TS Optics 70mm f/6 APO FPL53 Triplet

Date: 2018-06-29 & 2018-06-30
Atik L: 78×300s 1×1 binned
D5100 RGB: 180×120s 1×1 binned

Postprocessing Details

Well, sadly I cannot provide any exact postprocessing details this time. Reason for that is that PI crashed on me several times, killing my project in the meantime. The only real details that I can provide is for RGB. I will try providing the L details for the CCD data as well, but I don’t remember everything.

L (383L+)

  • DynamicCrop
  • DynamicBackgroundExtraction
  • Deconvolution
  • TGVDenoise and MMT by Jon Ristas method
  • HistogramTransformation
  • (Possibly another round of TGV)
  • MultiscaleMedianTransform for Sharpening
  • LocalHistogramEqualization for Large Scale Structures
  • LocalHistogramEqualization for Small Scale Structures
  • CurvesTransformation for Contrast Enhancements

RGB (D5100)

  • DynamicCrop
  • DynamicBackgroundExtraction
  • PhotometricColorCalibration
  • SCNR Green
  • Extract L

L (D5100)

  • TGVDenoise and MMT by Jon Ristas method
  • HistogramTransformation for Stretching
  • TGVDenoise and MMT by Jon Ristas method (second pass)
  • HistogramTransformation to adjust background brightness

L (383L + D5100)

  • StarAlignment of Deepfield L to Widefield L
  • Export both aligned and Widefield L to Photoshop
  • Mask out black parts of Deepfield L
  • Feather edges of Deepfeld L
  • Levels on Deepfield L to match background brightness values
  • Save and export back into PI (cont. LRGB 383L+ and D5100)

RGB (D5100, cont.)

  • TGVDenoise and MMT by Jon Ristas method
  • ArcSinhStretch
  • HistogramTransformation
  • MultiscaleLinearTransform (removing large scale Chrominance noise)
  • MultiscaleLinearTransform (removing massive scale Chrominance noise)

LRGB (383L+ and D5100, Widefield Data)

  • LRGBCombination with large scale Chrominance noise reduction
  • CurvesTransformation for Star Colors
  • CurvesTransformation for Galaxy Color
  • Export as 16bit tif
  • Annotate using PixInsight
  • Export as 16bit tif

LRGB (383L+ Deepfield Data)

  • StarAlignment LRGB Widefield on Deepfield data
  • LRGBCombination with Widefield Data
  • Export detailed M101 as 16bit tif

LRGB (Widefield + Deepfield Data)

  • Align in Photoshop
  • Annotate in Photoshop

Annotated Image

M101 (LRGB, Annotated)

6 Replies to “M101 – Pinwheel Galaxy (LRGB)”

  1. Your result of M101 gives deep impact with all details and skilled work behind it.

    Excellent, thanks for sharing this

    1. Thank you very much Peter, I’m doing my best to provide beautiful images of space for everyone, even if it costs me weeks from time to time.

  2. (I forgot to mention that its really gives fascination of how many galaxies you really have in this picture, at least 50..)

  3. Can I send this picture to a friend? It’s beautiful and I’m sure she would love it. I’m also going to have her sign up

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