NGC 7000 - North America Nebula

Finally a photo of the sky!

The largest red blob in the middle of this photo is the North America Nebula (NGC 7000 or Caldwell 20), an emission nebula in the constellation of Cygnus. Above it is the Pelican nebula (IC 5070), both of them swimming in a sea of minor red clouds. Both nebulae are of the emission type, meaning they are giant clouds of atomic hydrogen and oxygen, which are being excited by nearby young, hot stars (just like teenagers close to other teenagers), and emit light (not like teenagers).

I imaged those teenagers, I mean nebulae, over three nights in the beginning of September 2023.

Image Processing

Total acquisition time is 5 hours 50 minutes, in which 2 hours were for the RGB version, and 3:50 for the narrowband. All captured in 5 minute exposure at -15C sensor temperature, gain 10, offset 50.

Most processing was done in Pixinsight, with final touches in GIMP.

I photographed the nebula using two different filters, the first one was UV/IR filter, and the second one was a narrowband Ha + OII duoband 5nm filter from SVO. After stacking them separately in WBPP I got two masters, one wideband RGB and the second one in narrowband.

The initial step was to register them with one another so that the stars align.

Then I moved to processing the narrowband image:

1. Dynamic Background Extraction
2. SCNR to remove surplus green.
3. Soft stretch (I am using EZ Scripts suite)
4. Starnet2 to remove the stars
5. Unsharp Mask
6. Final stretch

With that done, I switched to the wideband RGB image:

1. Dynamic Background Extraction
2. Photometric Colour Calibration
3. Soft stretch
4. Tiny bit of Curves transformation to slightly reduce the stars bloat
5. Starnet2 with star mask to extract the stars

Now with narrowband image done and the star mask ready, I moved to PixelMath to combine them using a formula I came across several times on different internet forums, which for some magical reason works much better than simple addition: ~((~narrowband)*(~star_mask)). This combining is a quick step, and I run it several times with different amounts of Curves transformation to see what suited me best.

I saved the combined image as .tif and opened it in GIMP for some final touches, a bit of cropping, unsharp mask, saturation and curves tweaking.

Gear Used

• iOptron GEM28 equatorial mount
• QHY 168C cooled astrocamera
• an old and moldy M42 lens 200mm, f/3.5
• ZWO ASI 120MC and ZWO Mini guider for guiding
• Astrojolo Astrolink 4Pi running Astroberry OS for session control and image acquisition.
• my DIY powerbank to power everything.

Final Thoughts

This is so far my best astro picture with the longest acquisition time. Yet, after spending days looking at much better astrophotography on Astrobin and Astropolis, it does not feel that good to me. But well, I feel I made progress since the last time, and this is what counts.

I need a better lens, this one has an awful CA which makes those atrocious halos around stars, but that is something that needs to wait until I get some budget.

That’s it, hope you liked it. And as a bonus, the narrowband starless version:

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