Nebula processing workflow: a Foraxx palette from a one-shot colour image

IC 1848 – The Soul Nebula

My current workflow for processing one-shot colour images of deep-space objects, particularly nebulae, heavily relies on the process of reconstruction a foraxx palette outlined in this video by Paulyman Astro (https://youtu.be/Gy42AeZ_XB4?si=lNb4B7a0jVKWi4I1).

The video is very detailed, and it has been exceptionally useful for me, but I found myself scrolling through it and pausing so much that I wanted to have a written summary of the steps that I could quickly refer to. Apologies in advance, if the following steps appear out-of-context – they are really short notes that would make sense to those who have used the Pixinsight software and worked with the foraxx palette.

Before this image processing is even started, I generate an integrated image using the following pre-processing sequence (see this guide by Adam Block for details: https://youtu.be/VKOTCuqD2Qs?si=EdbONwT8GO_DUAkR) :

First of all, all the individual exposures (light frames), which are typically 5-min long each, are calibrated with “flats”, “dark flats” and “darks” using the WeightedBatchPreprocessing script. 

Then, the resulted de-bayered images are aligned using the StarAlignment process.

Finally, the aligned images are integrated using the ImageIntergation process with Winthorised Sigma Clipping background rejection method. This produces the “integration.xisf” image, which is the basis for the nebula processing workflow itself:

  1. Right-click on the identifier tab at the top-left of the image frame and set the new identifier to ‘osc’ (for ‘One-Shot Colour’).
  2. Use Process>All processes>ScreenTransferFunction to preview a stretched image. I unlock the RGB channels before pressing the “nuke” button to avoid a high colour cast. This is not important though, because nothing is actually being done to the image – this is just a preview.
  3. Use Process>All processes>DynamicCrop to crop the image.
  4. Use AutomaticBackgroundExrtactor with Function degree (under Interpolation and Output) set to 1 and Target Image Correction to ‘Subtraction’. This works if there is simply some light pollution gradient in the image and little to no vignetting. Otherwise, use the DynamicBackgroundExtraction process.
  5. Split the RGB channels using an icon in the toolbar.
  6. Set the identifier of the Red channel to ‘ha’ for “Hydrogen alpha”.
  7. Combine the Green and the Blue channel using the following Pixelmath expression: 0.5*B+0.5*G. Give the resulting image an identifier ‘oiii’. 
  8. Use StarExterminator process to extract the stars. Check “Generate Star Image” and “Unscreen Stars” boxes. Drag the triangle from the process window onto the ha window and then onto the oiii window.
  9. Use Generalized Hyperbolic Stretch (GHS) script or process to stretch the ‘ha’ and the ‘oiii’ (starless) images.
    • First stretch: Just right of the peak. Local stretch intensity ~10. Stretch factor ~3.
    • Second stretch: Secondary drop-off (log view). Local stretch intensity ~5.
  10. Foraxx process: Create the false Green channel (‘ho’) using the Pixelmath expression: (ha*oiii)^~(ha*oiii). Press the square button.
  11. Boost the brightness of the ‘ho’ image by doing the first-level stretch in GHS.
  12. Create the colour image by using the Pixelmath expression (uncheck ‘Use a single RGB/K expression’, set Color space to ‘RGB color’):
    • R: ha
    • G: ho*ha+~ho*oiii
    • B: oiii
  13. Apply CurvesTransformation. Start with saturation, proceed to individual channels.
  14. Apply NoiseExterminator with default values or Denoise ~0.9, Detail ~0.55.
  15. Stretch ‘ha_stars’ and ‘oiii_stars’ using HistogramTransformation. Use checkmark to track the histogram and use live preview to monitor the stretch amount. Drag middle slider to the left.
  16. Apply the Foraxx process (step 10) to ‘ha_stars’ and ‘oiii_stars’.
  17. Use CurvesTransformation to boost saturation of ‘foraxx_stars’.
  18. Put the stars back using the Pixelmath expression: ~(~foraxx*~foraxx_stars).

And this is it! Here are some examples of my application of this process applied to various emission nebulae.

Sharpless 157 – The Lobster Claw Nebula
NGC 7000 – Cygnus Wall
NGC 7822 – The Cosmic Question Mark Nebula

NGC 7822 – The Cosmic Question Mark

This emission nebula is one of the youngest star-forming regions in our galaxy. Some components of it are only few million years old. In the cosmic time scale, this is basically star birth happening in front of our eyes. This nebula also contains the hottest star found within 1 kpc of our Sun, the BD+66 1673, which has the surface temperature of 45,000 K and the luminosity 100,000 times that of the Sun. It is primarily responsible for ionizing the gas of the nebula and for compressing it by the strong stellar wind, leading to creation of new stars. 

This light travelled for 3,000 years before reaching my yard in Victoria, BC in June 2024.

NGC 7822 is a large target, filling the full-frame sensor of my camera attached to a 478 mm-long telescope. This is a 3.5 hr-long RGB exposure at f/5.9, processed using a Foraxx palette.

The Flowing Clue: La Source Unveiled – panels 4,5

“The Flowing Clue: La Source Unveiled” page 1, panels 4, 5

This is the ink of the last two panels on the first page of my fluids comic book. The first closeup of one of the main characters required quite a bit of thinking through in order to simplify the original character design. Professionals like Victoria Ying say that by the end of the inking process one becomes very good at drawing the main characters, because they appear so often. I am certainly looking forward to that, but in the meantime, I was quite glad to simply finish the first page.

The Flowing Clue: La Source Unveiled – panel 3

“The Flowing Clue: La Source Unveiled” page 1, panel 3

Here is the ink of the third panel of my fluids comic book. When I was laying out this panel, I made a decision to use a 3D model for the backgrounds, and now that I am several pages into inking, I am certainly glad that I did so. Considering that the story takes place in the same room full of small details, maintaining consistency of the set without the ability to simply re-position the camera would have been impossible.

My fluids comic book

“The Flowing Clue: La Source Unveiled” page 1, panels 1-2

I’ve been working on a fictional short story, hopefully the first in a series, on the subject of my academic research and teaching – fluid mechanics. As a colleague of mine said about teaching fluids at the university level, “fluids is a dry subject”. In the hope of making it a bit more entertaining, I’decided to try a manga format. It’s a crime story set in the not-very-distant future with the working title “The Flowing Clue: La Source Unveiled”

Here are the inks of the first two panels. Stay tuned for the updates on this work in progress.

M94 – The Croc’s Eye Galaxy

I captured this image of the Croc’s Eye Galaxy (M94, also called the Cat’s Eye Galaxy) yesterday in my yard in Victoria, BC, using a total of 3 hours of exposure. It’s an unusual galaxy – it has a an inner ring with a diameter of 5,400 light-years and an outer one with a diameter of 45,000 light-years. Pressure from the galactic core compresses the gas and dust clouds in the outer ring, where gravity pulls them together to form new stars. These stars pull in more gas and dust, resulting in a relatively empty region separating them from yet another layer of gas at the periphery of the galaxy.

M94 has a remarkably low amount of dark matter for a galaxy – the stars comprise almost all of its mass. Their light travelled for 16 million years before reaching my telescope.

My 2024 reading list

Fiction:

  1. “Study in Scarlet” by Arthur Conan Doyle.
  2. “The sign of Four” by Arthur Conan Doyle.
  3. “A Scandal in Bohemia” by Arthur Conan Doyle.
  4. “Foundation” by Isaac Asimov.

I’ve been postponing reading Asimov’s books, and this one demonstrated that I was wrong. It is a classic for a reason. Amazing prose and very cool characters.

Non-fiction:

  1. “Fallen Leaves” by Will Durant (audio).

It’s interesting to listen to a personal opinion on the nature and meaning of life of a historian and philosopher written at the end of his long life, spent documenting experiences of other people. It is also curios that the manuscript of this book was actually lost and published only after Durant’s death. Also amazing how demonstrably misled even such educated and academically-minded person could be about topics that are only marginally beyond his field of study. I suppose, it’s an example of the Dunning-Kruger effect in action.

  1. “How to Do the Work” by Dr. Nicole LePera (audio).

I liked the idea of interconnectedness of the psychological balance and physical wellness. One example that I particularly liked was on the undeniable effectiveness of placebo (as well as its opposite, the nocebo) in various medical trials. This book has about the maximum amount of woo-woo that I can tolerate without immediately becoming too skeptical to continue listening. What also helps is that the author has a traditional scientific background, which add certain structure to the presentation of the ideas.

  1. “The Mountain is You” by Brianna Weist (audio).

I was a bit skeptical about this book because of a somewhat cheesy title, but I was pleasantly surprised. It is largely about the nature of self-sabotage and ways of avoiding it. One message that resonated particularly well was the necessity to normalize the new psychological state, e.g., feeling happy, in order to shift the baseline towards it. I will certainly consider Weist’s follow-up books as future reads.

  1. “Make It Stick” by Peter C. Brown, Henry I. Roediger III and Mark A. McDaniel (audio).

I came across referenced to this book before, but this is the first time I listened to the entire thing. It was reviewed in the “Perpetual Chess” podcast that I sometimes listen to while walking the dog. It’s a very structured, for a popular science book, overview of study and teaching methodologies. The main takeaways for me were that Spacing and interleaving of practice constitute desirable difficulties. Also, tat generative self-quizzing is more effective than multiple-choice type or re-reading of the material.

  1. “Born standing up” by Steve Martin (audio).

I heard about this autobiography any time in the podcasts that I follow, most notably “The Tim Ferris Show”, but finally I decided to listen to it. It’s an excellent book indeed. Very entertaining, insightful and inspiring. It is also another example of the benefit of the audio format, where the author and the reader is the same person. It also helps that he is a good actor.

  1. “The Search” by Bruce Feiler (audio).

Some thoughts about the conventional concept of a career, and how outdate it is in the modern world. There is an attempt to hammer in this point with some statistics, but the rigor of the statistical analysis is a bit suspect, and I think the point is clear enough without all the surrounding fuss. The stories are entertaining, but there author is trying a bit too hard to deliver the point that diversity is paramount when considering the variety of jobs and occupations in the modern world.

  1. “The Pivot Year” by Brianna Wiest (audio).

Well, Brianna Weist has certainly been the author of the year for me. I re-listened to “The Mountain is You” and liked this book too. It is clearly a compilation of blog posts, which is actually quite inspiring.

  1. “Projections: A story of human emotions” by Karl Disseroth (audio).

My app shows that finished listening to this book to the end, but at the time of this writing, I have no recollection of what I learned from it. I should definitely be more diligent with taking notes, but it probably says something about the book too.

  1. “The Creative Act: A Way of Being” by Rick Rubin (audio).

This is excellent. I found this summary of thoughts about the creative process very relatable, despite the author’s background in music production, which is quite foreign to me.

  1. “The Rational Optimist” by Matt Ridley (audio).

I remember that I enjoyed it, although struggle to recall what specifically I learned.

  1. “10% Happier” by Dan Harris (audio).

That was a very nice read (listen). I enjoyed the overview of the author’s personal journey to “amateur buddhism”. It inspired me to read a couple more books on Buddhism immediately afterwards.

  1. “Going to Pieces without Falling Apart: A Buddhist Perspective on Wholeness” by Mark Epstein, M.D. (audio).

The author was featured i “10% Happier” as Dan Harris’ mentor/teacher, so I decided to take a look (listen) at his work. It was quite nice. My favourite part is the anecdote about locking the keys in the car immediately after a mindfullness retreat and being Ok with it.

  1. “Mindfulness: Six Guided Practices for Awakening” by Joseph Goldstein (audio).

This is another reference from “10% Happier”. For what it worth, my app shows that I abandoned it at 52%.

  1. “Antifragile” by Nassim Nicholas Taleb (audio).

A cool concept, but the author’s tangents about how amazing and non-conformist he is detracts from the experience quite a bit. If anything, it indirectly confirms the idea of the inherent value of formal education.

  1. “Napoleon the Great” by Andrew Roberts (audio).

A biography of Napoleon. One of my favourite books this year. 

The Soul Nebula

W5 is a large emission nebula located in the Cassiopeia constellation, close to the Heart Nebula (IC 1805). There are several open star clusters inside the Soul Nebula, including IC 1848, which is often used to identify it.

The Soul Nebula is a star nursery, where new stars are created practically before our eyes. In fact, most stars have been born in regions like W5, where hundreds or thousands stars form at the same time.

The Soul spans 300 light-years, which is about 100 times the distance from the Sun to the nearest star.

About a dozen of giant O-type stars are primarily responsible for creating this emission nebula. These giant stars are approximately 30 times heavier and 10,000 times more luminous than our Sun. This intense luminocity is mostly in the form of ultraviolet radiation. It forms a powerful stellar wind that ionizes gas molecules and drives them away from the giant stars, creating the bubble structure in the middle of the nebula. 

This structure contains gas pillars that point towards the stars that created them. The pillars form because the denser gas areas take longer to clear, while the material around them is swept away by the stellar wind. The compression of the gas molecules in the pillars accelerates their gravitational collapse and leads to formation of new stars.

In the Soul Nebula, there are at least three generations of star formation. Their light travelled for 6,500 years before reaching my camera in Victoria, BC in June of 2024.

The Heart Nebula

IC 1805 is a faint, but huge emission nebula in the Cassiopeia constellation. It is about 330 light-years in diameter and has an angular size of 2 degrees – 4 diameters of the full Moon! The open star cluster in the centre of the heart (Collinder 26) creates intense stellar wind that drives the shape of the gas cloud and causes it to emit the intense red colour. Some of these stars are 50 times more massive than the Sun.

This light travelled for 7,500 years before reaching my camera in Victoria, BC in the early October.

The Andromeda Galaxy

M31 is the deep-sky object that made me want to do astrophography. This light travelled for 2.5 million years before reaching my yard in Victoria, BC in the early September.

The Andromeda is closest galaxy to our Milky Way Galaxy. It is 152,000 light-years in diameter, contains approximately 1 trillion stars and is moving towards us at 110 kilometres per second. Our galaxies will collide in about 4.5 billion years, eventually forming a single giant elliptical galaxy.

The chance of any stars colliding is actually negligibly small, because despite their great numbers, the distances between the stars are tremendous. The two galaxies will simply pass through each other, as they commonly do. In fact, the M31 itself merged with another galaxy 3 billion years ago.

However, both the Milky Way and the Andromeda galaxies have supermassive black holes in their centres, and when they eventually merge, they would form a quasar and release as much energy as about 100 million supernova explosions. According to the current models, there is a 12% chance that our Sun would get ejected from the new galaxy during the collision, in which case the star itself, as well as its planets would be undisturbed. However, if the Sun comes close to the new black hole, it would be torn apart by its gravity.

This will be of little consequence to the life on our planet, though, because much earlier than that, about 1 billion years from now, the Sun’s luminosity will increase by approximately 40%, and there will be no way for liquid water and terrestrial life to exist on Earth.

Time to introduce planetary engineering into our curriculum?