This set of photos features the Rosette Nebula (typically referred to as New General Cataloge (NGC) 2237, or Caldwell 49).  The Rosette Nebula is a large region of ionized hydrogen (H II) that is located 5,000 light years from Earth, and measures roughly 130 light years in diameter (for some perspective, one light year is 5.88 trillion miles – Our solar system is 3.7 billion miles from the Sun to Pluto, so this area of Nebulosity is huge).  This nebulosity features an H II region of interstellar atomic hydrogen that is ionized, and has formed a molecular cloud of partially ionized gas where star formation occurs.  In this case, the open cluster of stars at the center of the Rosette Nebula (NGC2244, aka Caldwell 50), have formed from the nebulas matter.  12 Mon, is the largest of the stars.  The Rosette Nebula has multiple NGC designations for various parts of the nebulosity (NGC2237, 2238, 2239, 2244, & 2246), but my pictures were centered on NGC2237.  The Rosette Nebula also happens to look like a human skull, and some people refer to it as the Skull Nebula, but there is another Nebula (NGC246) that already has that designation

There are two versions of the Rosette Nebula, RGB and HOO.  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
The RGB version is dominated by the Red component (Hydrogen Alpha) with some light pink, and very subtle faint 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. 

Still learning a lot of how this all works, but very happy with these images:  RGB, RGB Starless (all of the stars removed), and HOO.

The sky chart shows the location of the Rosette nebula in the Monoceros constellation, not to far (about 30”) from Betelgeuse and the Orion constellation.  This image also contains NGC2252 which is an open cluster of stars on the outer edge of the Rosette Nebula.

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: 3 Hours 30 Minutes; Lights (42 @ 300 seconds); Darks (30 @ 300 seconds); Flats (40); Bias (30) – Lights were captured October 26, 2022, nearly a new moon (only 1.37% light)·

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.

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.       DBE 1st Div and 2nd Sub
5.       Background Neutralization
6.       Color Calibration
7.       Photometric Color Calibration (PCC)
8.       Resample to 70% (otherwise my computer will crash)
9.       Extract a Luminance Image (see flow below)
10.   Noise Xterminator (75%)
11.   Star Xterminator – Worked real well except one small corner
12.   Moved forward with OCS image starless and saved stars for later
13.   OCS Image Flow
a.       Stretched with 4 different methods and compared to see what I liked the best                                                              
i.      GHS_Manual (I stretched); GHS_Script (Bill Blanshan’s script); Ez-Suite Soft Stretch; and a Masked Stretch                                                            
ii.      I then used Histogram_Transformation tool to get them all to the same background darkness                                                          
iii.      Picked GHS_Script as the best for the remainder of processing
b.       Non-Linear Flow                                                              
i.      HDR & Pixelmath to blend (5 – 8) (Nebula Masked)                                                            
ii.      Additional Sharpening using Multiscale_Linear_Transformation (MLT) and UnsharpMask (USM) & Pixelmath blend (Nebula Masked)                                                          
iii.      DarkStructure Script                                                          
iv.      Curves Transformation – Minor Saturation, Red, and RGB S Curves (Nebula Masked)                                                            
v.      LocalHistogramEqualization (LHE) – Very minor                                                          
vi.      At this point, I created a duplicate image and used Bill Blanshan’s HOO NormalizationV3 script to create the HOO image (followed remainder of flow below)
14.   Stars (RGB)
a.       Stretched with Histogram_Transformation to a smaller number of star that were appealing to my eye
b.       Small Curves Transformation for Saturationc.       Used a formula to put screened stars back (@PaulymanAstro)
15.   Luminance Layer
a.       Ran EZ_Deconvulotion (75 iterations)
b.       Ran Noise Xterminator (75%)
c.       Removed stars with Star Xterminator (discarded the stars)
d.       Stretched with Masked Stretch
e.       Adjusted with Histogram Tool
f.        Tried some sharpening techniques, but didn’t like the end result – Looked over processed when I merged the Luminance and the OCS w/ Stars
g.       Merged the image with LRGB
16.   Final Color adjustments (very minor)
17.   Final Noise Xterminator (90%)
18.   Cropped picture & Annotated with my signature
19.   Output multiple picture types