This set of photos features Thor’s Helmet (typically referred to as New General Cataloge (NGC) 2359 or Sharpless 2-298), probably my hardest target to date (took me 3 attempts to process this image). Thor’s Helmet is low in altitude on the south side, so it is difficult to image from my location. Thor’s Helmet is an emission nebula about 12,000 light years from Earth, and the Nebula is 30 light year’s in size (more than 30x the size of our solar system). The nebula is produced by a massive, hot Wolf-Rayet star (WR7) emitting a stream of charged particles (stellar wind) that is expanding outwords to produce an interstellar bubble (the dome portion of the “helmet”). Wolf–Rayet stars are evolved, massive stars that have completely lost their outer hydrogen layer and are fusing helium or heavier elements in the core. The surface temperatures of known Wolf–Rayet stars range from 20,000 K to around 210,000 K, hotter than almost all other kinds of star, which makes the stars extremely bright.

These pictures were shot with the ZWO Dual Narrowband filter which is great for heavy light pollution areas (like mine), bright moonlight, and allows light transmission in two frequency regions:
1. Hydrogen Alpha (Ha) (red) at 656.3 nm with a bandwidth of 15nm
2. Oxygen III (Oiii) (blue) at 500.7 nm with a bandwidth of 35nm

This is an HOO processed image accentuating the Hydrogen Alpha (Red) and subtle blue elements (Oxygen III). The HOO version normalizes the light levels of all three color components and then I this case assigns Hydrogen Alpha data to the Red channel and Oxygen III data to the Blue and Green channels (with some blending of the channels based on how the camera processes the RGGB bayer matrix). This approximation is close to what is called the Hubble Palette. This images that make up this picture were collected on November 19 and 20th, 2022., The moon was less than a quarter moon (Waning Crescent) nearing the new moon.

The sky chart shows the location of Thor’s Helmet near Canis Major and the highly visible star Sirius. This image also contains IC468 which is an “Other classification” item – not sure what it really is.

My setup:

• Mount: EQ6R-Pro
• Telescope: Williams Optics 81 mm Zenithstar doublet
• ZWO-ASI224MC color camera for guiding with the Zenithstar guide
• Hotech Corporation 2” Field Flattener
• ZWO ASI2600MC Pro; Camera cooled to -10 deg C, with ZWO Duo-Band Narrowband Light Pollution Reduction Filter
• Bortle-9 – South Los Angeles shot from my backyard
• Integration Time: 8 Hours 50 Minutes; Lights (106 @ 300 seconds); Darks (30 @ 300 seconds); Flats (30) & Bias (0) – Lights were captured on November 19th and 20th, nearly a new moon (about 18.5% moonlight)
• Image Processing: Pixinsight – Using videos from multiple youtube teachers and website. @ChaoticNebula, @Cosgrove’sCosmos, @ViewintoSpace, @EnteringintoSpace, @PaulymanAstro, @Lukomatico – Lots of great on-line teachers/examples.

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Here is my simplified Pixinsight workflow that I have been tailoring over the last 4 months learning PixInsight and watching some really amazing people teach how the tools work.

1. WBPP with 2x drizzle
2. Perform a Linear Fit (with Green as a reference)
3. Dynamic Crop
4. Resample to reduce 65% image size (otherwise my computer crashes)
5. Extract a Luminance Image
6. Extract R, G, & B images
7. DBE 1st Div - Didn’t need to perform subtraction as the gradient was very limited
8. R,G,&B Image
1. Using Image Statistics – Linear Fit for the darkest of the median values
2. LRGB Combinations – R = HA, B = Oiii (w/ 95% Channel Weight), & G = Oiii (w/85% Channel Weight)
1. Chrominance Noise Reduction


3. Background Neutralization
4. Color Calibration
5. Photometric Color Calibration (PCC) – Didn’t work with this data set – Couldn’t fix the image header to solve, so scrapped
6. SCNR – Using Bill Blanshan’s Script (@AnotherAstroChannel)


9. Luminance Image Flow
1. Deconvultion using EZ Deconvulotion – Increase luminance detail


10. Star Xterminator on both the HOO Image and the Luminance
1. Keep HOO stars


11. Noise Xterminator on both (85%)
12. Stretched with 4 different methods and compared to see what I liked the best
1. GHS_Manual (I stretched); GHS_Script (Bill Blanshan’s script); Ez-Suite Soft Stretch; and a Masked Stretch
2. I then used Histogram_Transformation tool to get them all to the same background darkness
3. Picked GHS_Manual as the best for the remainder of processing (HOO & Luminance)


13. Non-Linear Flow
1. Luminance Image
1. Additional Sharpening using Multiscale_Linear_Transformation (MLT) and UnsharpMask (USM) & Pixelmath blend (Nebula Masked)


2. HOO Image
1. Using Luminance Image as mask
1. Curves Transformation to darken the background


2. Using Color Masks – Increase Red, Blue and Green coloration (along with saturation)
3. Convultion in preparation for merger


3. LRGB Combination – Merge Luminance w/ HOO
4. Exponential Transformation (w/ Luminance Mask) – Increase nebulosity brightness
5. Local Histogram Equalization (w/ Luminance Mask) – Basically increasing contrast
1. Large Structures – 150 Kernel – 1.3 Contrast
2. Small Structures – 50 Kernel – 1.3 Contrast


6. Final Color Adjustments (w/ Luminance Mask)
1. Darken Background
2. Improve Nebula


7. Dark Structure Enhance Script


14. Stars (Hoo)
1. Stretched with Histogram_Transformation to a smaller number of star that were appealing to my eye
2. Small Curves Transformation for Saturation
3. Used a formula to put screened stars back (@PaulymanAstro)


15. Final Color adjustments (very minor)
16. Cropped picture & Annotated with my signature
17. Output multiple picture types