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M101: A work in Progress (Part 1)


Location

The Pinwheel Galaxy (not to be confused with the Southern Pinwheel Galaxy) is formally designated as M101. This galaxy is located in the constellation Ursa Major, and the asterism Big Dipper. It is down and to the left of Alkaid, the bottommost star of the Big Dipper.

Sky map showing the Pinwheel Galaxy (M101) located near Alkaid in the constellation Ursa Major, including labeled stars Dubhe, Merak, Alioth, and Mizar.

The Pinwheel Galaxy is located roughly 23 million light years away and is about 170,000 light years in diameter (that is nearly twice as large as our Milky Way!). It appears relatively small and has a low surface brightness (meaning that is difficult to observe both visually and photographically). M101 is known for its semi-frequent supernovae explosions, which can make for some fun surprises when observing it.

The Image

Alright, so now that we know what and where it's located, let's talk about the work in progress: My 4 hours of the Pinwheel Galaxy. The details of the image are below.

A high-resolution image of the Pinwheel Galaxy (M101), showcasing its spiral structure against a backdrop of various stars and galaxies in space.
My "work in progress"

Image Information

Integration time: 265 x 60" exposures for a grand total of ~4.42 hours @ 400ISO; 2.85 hours from Bortle 3/4 skies, and 1.15 hours from Bortle 5/6 skies

Software: N.I.N.A., Siril, Pixinsight, and RC Astro's XTerminator series

Equipment (imaging side): Astronomics AT60ED, Celestron GCX, and Nikon D5300 (modified)

Acquisition

The only problems that I encountered during my 4 nights of (actual) imaging was the first night: I forgot to dither. However, not all was lost, I was able to save about 40 minutes of data since the rest of the 225 minutes was very well dithered. Speaking of which, I dithered at 5 pixels every 3 frames (enough to drizzle later on), and my guiding numbers were ~1.4" RMS.

Processing

I am a complete newbie to Pixinsight (in fact, I am currently on the 45 day free trial), but I am pretty impressed with my image so far. An example of my (basic) processing steps are below, all done in Pixinsight:

  1. Crop/rotate

  2. BlurXTerminator (correct only)

  3. Plate solve

  4. Background Extraction 

  5. Spectroscopic Color Calibration (SPCC)

  6. BlurXTerminator

  7. StarXTerminator on RGB and L images

  8. NoiseXTerminator on RGB and L images

  9. Luminance

  10. Masked Stretch

  11. Generalized Hyperbolic Stretch (GHS)

  12. Select background, lower bp

  13. HDR

  14. Masked Stretch

  15. NoiseXTerminator

  16. RGB (color)

  17. Masked Stretch

  18. Arcsinh Stretch

  19. Combine LRGB

  20. Minor stretching 

  21. SCNR

  22. Selective Color Correction (highlights+mid tones mask)

  23. NoiseXTerminator yet again (to get rid of chrominance noise)

  24. Increase color saturation 

  25. Stretch and combine stars

  26. Upsample 2x

  27. Plate solve

  28. And annotate!

Before/after showing stars/starless
Before/after showing stars/starless
A detailed astronomical image of the Pinwheel Galaxy (M101) surrounded by various labeled celestial objects in a star-filled background.
The same image, but with some of the objects labeled
A collage of multiple images depicting various views of the Pinwheel Galaxy (M101), characterized by a mix of spiral structures, stars, and dark backgrounds, showcasing the results of astronomical imaging and processing techniques.
This is a collage off all of the galaxies surrounding M101 in my image (click on the image to blow it up)

Conclusion

I hope that you enjoyed this article as much as I enjoyed capturing the image! I plan to do 10 hours of total integration time, so stay tuned for Part 2!

If you have any questions/comments, just leave a reply below (or email me) and I will get back as soon as I can.

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