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M101: A (finished) Work in Progress

Updated: Dec 4, 2025

It has been some time since my last image. After fighting against the smoke from the Canadian wildfires, clouds, rain, and high humidity, I finally managed to capture a whole 14 hours on the Pinwheel Galaxy (M101). I was able to add roughly 2.5 hours of integration time (from Bortle 4 skies) for my broadband data, and 7 hours of data for the H-alpha regions (across varying phases of the moon).

H-Alpha Regions

What are H-Alpha regions? H-Alpha (or Hydrogen Alpha) regions are condensed clouds of ionized Hydrogen gas. When Hydrogen atoms get excited (or ionized) they emit light at a very specific wavelength (called a spectrum), and this wavelength happens to be in the reddish-pink side of visible light.

How H-Alpha is Captured

I believe the best way to capture the details of H-alpha regions is to use a narrowband filter, example the SV220 filter, to isolate the H-alpha regions, subtract the red channel (if using a color camera), and perform a process called "continuum subtraction" to the image. Then, you can either use "Pixel Math" or pre-defined scripts to combine your "continuum subtracted" image to your normal color image. This can produce some beautiful pictures, and is how I was able to define the H-alpha regions in the Pinwheel Galaxy. In fact, this process is so helpful that it was used to discover an "arc" of doubly-ionized Oxygen gas surrounding the top of the Andromeda Galaxy.

Image Information

Integration Time (Broadband): 416 x 60" exposures @ 400ISO for a grand total of 7 hours of integration time (5.85 hours from Bortle 4 skies and 1.15 hours from Bortle 5/6 skies).

Integration Tine (Narrowband H-alpha): 392 x 60" exposures @ 400ISO for a grand total of 6.5 hours (close to 7), all from a Bortle 4 sky.

Software: N.I.N.A., Siril, Pixinsight, Apple Photos, and RC Astro’s XTerminator series plug-ins.

Equipment (imaging side): Astronomics AT60ED, Celestron GCX, Nikon D5300 (modified), and SV220 Svbony duo-band 7nm filter.

Processing

To be honest, it took so long to process this image and finally get it right that I didn't keep track of my exact processing operations. Nevertheless, here is a brief summary of what I did:

  1. Crop/rotate

  2. BlurXTerminator (correct only)

  3. Gradient removal

  4. Spectroscopic Color Calibration (SPCC)

  5. Crop again

  6. BlurXTerminator, this time focusing on sharpening the galaxy/stars.

  7. Continuum Subtraction.

  8. Integrated the H-alpha data into the RGB image.

  9. NoiseXTerminator.

  10. Multitudes of stretching.

  11. Improve color.

  12. Super Resolution.

  13. NoiseXTerminator again.

  14. Improve color.

  15. Crop to final image.

Conclusion

As always, I hope that you enjoyed this article as much as I enjoyed taking the image! It took a lot of patience and perseverance, but I think that I can finally say that I am pleased with my image. If you would like more information on how I got this image, and how you can get this too, then let me know in the comments below.

Bonus!

I couldn't help myself. Here's the un-cropped version, showing all of the little galaxies surrounding the Pinwheel Galaxy. Click on the image to zoom in.


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