Mars and the Spaghetti

40’000 years ago, a dying massive star exploded. This is what remains of it today : the supernova remnant Simeis 147 – commonly known as the Spaghetti nebula. In the night of the 14th of April 2021, while I was imaging, I noticed a bright dot in the sky that wasn’t previously there. It took me a minute to realize that Mars was actually photobombing my shot! You can see the red planet in the lower left corner, and the other bright blue dot on the right is the star Alnath.


  • Samyang 135mm f/2
  • QHY163M
  • Baader narrowband filters
  • Antlia LRGB filters
  • Sky-Watcher HEQ5 Pro
  • QHY5L-II-C and QHY 30mm guidescope

Acquisition (Total : 18.3h)

  • Location : Backyard, bortle 5
  • Ha : 13 hours
  • Sii : 4.3 hours
  • RGB : 1 hour

Processing (PixInsight)

RGB stars processing

  • Two images were created : one for Mars (using CometAlignment) and one for the stars
  • Merge the two images with PixelMath and a mask (using GAME)
  • Repaired HSV separation to fix the stars cores
  • ArcsinhStretch
  • HistogramTransformation
  • Convolution
  • Saturation curve

Luminance processing

  • Create a luminance from Sii and Ha
    • ImageIntegration : noise evaluation, MAD estimator, no rejection
  • ArcsinhStretch
  • HistogramTransformation

Color combination (tutorial)

  • StarNet++ on Ha and Sii
  • Creating the dynamic factor
    • f : 3*Sii – 2*Ha
      • Smoothed with MMT, stretched with curves
  • Combining the channels with PixelMath
    • R  : 0.6*Ha + 0.4*Sii
    • G : f*Sii + ~f*0.22
    • B  : 0.22
  • LRGBCombination

LRGB processing

  • Recover the RGB stars
    • Extract the a/b channels from the stars image (using ChannelExtraction)
    • Replace the a/b channels of the target image through a star mask (using ChannelCombination)
  • Star reduction (tutorial)
  • Final adjustments (Curves, MMT, ColorSaturation…)

Taken in March 2021 – April 2021

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