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Comet C/2023 A3 Tsuchinshan ATLAS with M5

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Comet C/2023 A3 Tsuchinshan ATLAS put on quite a show after it rounded the sun and passed by the Earth on its way likely out of our solar system.  With an orbital eccentricity greater than 1, its orbit appears to be hyperbolic, meaning it’s not coming back unless something perturbs its orbit.

In this picture, you can see the comet’s bright nucleus and coma, its long dust tail, and its anti-tail, but not a separate ion tail.

When comets travel close to the sun, solar radiation heats up the comet nucleus, and it outgasses. Outgassing delivers both gas and dust to the region around the nucleus, forming a coma, a (temporary) atmosphere around the comet.  The solar radiation and solar wind act on this coma to push the gas and dust away from the sun to form a tail.  Three separate tails can be visible: the ion tail, the dust tail, and the anti-tail. The ion tail, also called the gas tail or type I tail, is the tail formed by the ionized gasses pushed away from the comet, and it points away from the sun.  The dust tail, also called the type II tail, is the tail formed by the dust pushed away from the comet, and it stays more in the comet’s orbit and appears to curve away from the gas tail.  The anti-tail consists of the larger dust particles that were not pushed as much and remained in the comet’s orbit.  The anti-tail appears to point towards the sun, and it is only visible when the Earth passes through the comet’s orbital plane near the time when the comet passed by the sun.  Because of these special conditions to see the anti-tail, it is not observed with most comets.

Another item visible in the image is M5, a globular cluster in our galaxy.  It is the large bright “star” to the right of the comet nucleus.  Because this image was taken with an 85 mm lens, and M5 was sorted to the “stars” image in my processing, it just appears to be a large bright star.  I suspect with some additional processing, I could have made it look fuzzier, though there aren’t a lot of pixels at this scale.  The Messier objects are “fuzzy” objects that comet-hunter Charles Messier made a list of because they weren’t comets – so it’s fun to see one next to a comet.  M5 is 24,500 light years away from Earth and has an angular size of 23 arc-minutes, making it about 165 light years across.  It’s thought to be one of our galaxy’s older globular clusters, at 13 billion years old.

Processing this image was tricky for several reasons: 1) it was made from images taken with a camera on a tripod, so the sky was moving in each frame, 2) the comet was moving relative to the sky, and 3) the images were taken at dusk, when the sky gradient is also changing in every image.  I benefited greatly from following the methods and advice in Adam Block’s Comet Academy.  One additional trick I used was to run BlurXterminator in correction only mode on all the registered images as my first step since the 4 second tripod images had visible star trails. 

Getting to this image has taken almost a month of watching videos, learning new tools, and trying various tool combinations and settings.  Some of these steps had to be run on each individual image – all 233 of them – meaning some processing steps took many hours.  After all that work, I am happy with the results.

I started with this image because I thought it would be the easiest of my set of C2023A3 comet images to process … the other images are from darker skies in terms of light pollution but closer to dusk and include a foreground.  But the comet was brighter!  I’m really looking forward to processing them and sharing the result!  Hopefully they won’t take a month each to process!

Camera geek info:

  • Canon EOS 60D in manual mode, 4 second exposures, ISO 1600
  • Canon EF 85 mm f/1.8 lens, manual focus at infinity
  • Intervalometer
  • Tripod
  • Pearland, Texas Bortle 7-8 dark skies

Frames:

  • October 15, 2024
    • 233 4 second lights
    • 30 0.0025 second flats
    • 30 0.0025 second darks

Processing geek info:

  • PixInsight
  • BlurXterminator
  • NoiseXterminator
  • StarXterminator
  • StarNet2
  • NormalizedScaleGradient

M31 Andromeda Galaxy Astrophotography Learning Curve

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The first object that I got a satisfactory image of with my tracking mount and telescope and DSLR was M31, the Andromeda Galaxy, from the dark skies of Dell City, Texas in October 2022.  My first image, above, was a 3 minute long exposure.  I was so excited to have a good image that I took a picture of my camera’s viewfinder to send the picture to people.  

When I came home to Friendswood, Texas, I did some experiments to see if I could get the same results.  It was not a surprise when the answer was “no” – my home skies are much more light polluted – I expected to get a completely white screen and was surprised when I could still see a hint of the galaxy.

I started to learn how to use PixInsight, a powerhouse astrophotography processing tool, in the winter of 2022.  I learned enough to be able to stack 18 3 minute images to make my Christmas card photo and the picture I am still using as my computer background at work.

I’ve learned a more about astrophotography processing since then, most notably adding Russ Croman’s excellent BlurXterminator, NoiseXterminator, and StarXterminator tools to my toolbox and learning a ton from Adam Block’s videos.  So I reprocessed the data above using my current knowledge and toolset.

Finally, in October 2024, we were back in Dell City, and I collected new M31 data using an astrocamera and red, blue, green and hydrogen-alpha filters.  I had to learn more in order to be able to merge the Ha data into the RGB data.  Luckily, there are Adam Block’s videos!  One new trick I had to use was “continuum subtraction” – removing the background red from the stars from the Ha data.  

Sometimes, when other things aren’t working out (comet processing), it’s good to step back and see how far you’ve come. I’ve learned a lot over two years … and I’m looking forward to learning a lot more!

What are you learning about?

Celebrating 100 years of understanding galaxies with M31, the Andromeda Galaxy

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When we travel to the fabulous dark skies of Dell City, Texas, I try to pick a combination of challenging targets and targets that I’m confident I’ll get good results with.  In October, one of my picks for the “good result” target was M31, the Andromeda Galaxy.

It seemed fitting to image the Andromeda Galaxy now because we are approaching the 100 year anniversary of Dr. Edwin Hubble’s November 23, 1924 New York Times article confirming that some objects classified as nebulae were, in fact, “island universes” – galaxies separate from our own.  Hubble used the Cephid variable stars in the Andromeda Galaxy and in M33 to measure the distance to those two galaxies and determine that they had to be outside of our own galaxy – on the order of 1 million light years away.  Based on that distance and its apparent size, Hubble calculated that the Andromeda Galaxy’s diameter was 45,000 light years.

100 years later, the Andromeda Galaxy is known to be 2.56 million light years away.  Its apparent size is 3.167 degrees by 1 degree, giving it a diameter of 141,000 light years.  So even further and even bigger than Hubble calculated!

It is amazing to me that we’ve only understood that there were other galaxies for 100 years!  And I think it is cool that we keep learning more and more about the universe around us.

This image of the Andromeda Galaxy was captured using red, green, blue and hydrogen-alpha filters. Although Ha actually is in the red part of the spectrum, it is frequently mapped to purple-pink so it stands out, and I have used that mapping here.  These Ha regions are star-forming nebula in the Andromeda Galaxy, similar to our own Orion nebula and Eagle Nebula. 

So while Hubble proved that Andromeda was a galaxy and not a nebula … it also contains its own nebulae. And we can see them!  How amazing is that?

Camera geek info:

  • Williams Optics Zenith Star 73 III APO telescope
  • Williams Optics Flat 73A
  • ZWO 2” Electronic Filter Wheel
  • Antila RGBH filters
  • ZWO ASI183MM-Pro-Mono camera
  • ZWO ASiair Plus
  • iOptron CEM40
  • Dell City, Texas Bortle 2-3 dark skies

Frames:

  • October 8, 2024
    • 196 60 second Gain 150 Ha lights
    • 30 0.5 second Gain 150 Ha flats
    • 168 60 second Gain 150 R lights
    • 30 0.05 second Gain 150 R flats
    • 174 60 second Gain 150 G lights
    • 30 0.02 second Gain 150 G flats
    • 173 60 second Gain 150 B lights
    • 30 0.02 second Gain 150 B flats
    • 30 0.02 second darks
    • 30 0.05 second darks
    • 30 0.5 second darks
    • 30 60 second darks

Processing geek info:

  • PixInsight
  • BlurXterminator
  • NoiseXterminator
  • StarXTerminator
  • NBColourMapper

Comet C/2023 A3 Tsuchinshan Atlas from Friendswood, Texas with a Telescope

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I have a bunch of wide field comet images from Dell City, Texas and Pearland, Texas that are proving … challenging … to process, given that they were taken near dusk with a DSLR on a tripod.  Everything is changing – the Earth is rotating (so the stars are moving relative to the camera on a non-tracking tripod), the comet is moving relative to the stars, and the sky brightness is changing.  

But now Comet C/2023 A3 Tsuchinshan Atlas is getting higher in the night sky, so it is no longer visible only at dusk.  So I could set up my tracking mount and telescope to image it.  The tail is still really long – much longer than I can capture in the field of view of my telescope!

Even with a tracking mount and dark sky, processing a comet moving relative to the stars is still really challenging, and I really benefited from following the “Standard Comet” example in Adam Block’s Comet Academy.

Camera geek info:

  • Williams Optics Zenith Star 73 III APO telescope
  • Williams Optics Flat 73A
  • ZWO 2” Electronic Filter Wheel
  • Antila RGB filters
  • ZWO ASI183MM-Pro-Mono camera
  • ZWO ASiair Plus
  • iOptron CEM40
  • Friendswood, Texas Bortle 7-8 dark skies

Frames:

  • October 24, 2024
    • Interleaved LRGB lights
      • 11 60 second Gain 150 R lights
      • 10 60 second Gain 150 G lights
      • 10 60 second Gain 150 B lights
    • 30 0.05 second R flats
    • 30 0.02 second B and G flats
    • 30 0.05 second darks
    • 30 0.02 second darks
    • 30 60 second darks

Processing geek info:

  • PixInsight
  • BlurXterminator
  • NoiseXterminator
  • StarXTerminator
  • ImageBlend

Experiencing the Northern Lights from Dell City, Texas

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Earlier this month, we were very lucky and happened to be at my favorite dark sky site – Dell City, Texas – when I got an alert on my phone that we might have a Kp8 geomagnetic storm coming the next day, with a chance to see the Northern Lights much lower than usual.

I have the app on my phone because we’ve traveled to places where seeing the Northern Lights was possible.  We even saw them on the horizon from Inverness, Scotland.  We’ve also been on two trips where Northern Lights tours were on the agenda – but both tours were cancelled due to weather.  Earlier this year, when there was another big geomagnetic storm, we went north to Conroe, Texas where people reported seeing the lights.  I found a great foreground – but alas, no lights.

So imagine my delight when I was setting up my telescope in Dell City, Texas, where the skies are very familiar to me, and I looked up and saw moving red lights to the north.  Red lights to the north are not normal.  The Northern Lights were visible from Texas!  I literally sprinted into our Air B&B to get my husband and my camera.

I took glamour shots of my telescope with the aurora.

I took glamour shots of our Air B&B with the aurora.

I made some time lapse movies.

Camera geek info:

  • Canon EOS 60D in manual mode, 5 – 10 second exposures, ISO 1600
  • Rokinon 14 mm f2.8 lens, manual focus
  • Intervalometer
  • Tripod

And I’m left with the question: when can we see this again?  It was amazing.

What amazing things have you seen recently?

Capturing Comet PANSTARRS C/2021 S3 with two Ancient Globular Clusters M9 and NGC6356

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I was looking through my comet posts after my post yesterday, and I discovered I hadn’t posted this image of Comet PANSTARRS C/2021 S3 with two globular clusters that I made last spring.  Enjoy!

I hadn’t planned on imaging comets when we were in Dell City last spring, but when I saw this combination of two globular clusters and comet PANSTARRS C/2021 S3, I knew I had to try it.

Globular cluster M9, the brighter one to the left, is 25,800 light years away from us.  It’s 90 light years across, giving it an apparent size of 12 arcminutes.  Globular cluster NGC6356, the smaller one to the right, is 49,200 light years away from us.  Its apparent diameter is 8 arcminutes, giving it a diameter of 115 light years across.  Globular clusters are mind-bogglingly old parts of our galaxy and can be used to infer the age of the universe.  There are some interesting open questions about them, including their exact ages and whether they formed as part of our galaxy or were accreted later (probably a mix of both).  In the paper I found giving the ages for these two globular clusters, it shows that M9 is 14.60 ± 0.22 billion years old with one model, 14.12 ± 0.26 billion years old with a second model, and 12 billion years old in the literature.  It shows that NGC6356 is 11.35 ± 0.41 billion years old with one model, 13.14 ± 0.64 billion years old with a second model, and 10 billion years old in the literature.  No matter which age ends up being correct, ~10 billion years old is amazingly OLD!

Comet PANSTARRS C/2021 S3 was discovered by the Panoramic Survey Telescope and Rapid Response System located at Haleakala Observatory, Hawaii on images taken on September 24, 2021.  It reached perihelion (its closest point to the sun) on February 14, 2024 (the day after this image was taken) at 1.32 AU distance.  Its orbital eccentricity is higher than 1, meaning it’s on a parabolic trajectory and isn’t coming back.

I feel very fortunate that my trip out to the dark skies was timed so I could image this comet with two ancient globular clusters.  I also feel fortunate that I imaged it in a time when so many processing tools are being developed to make processing the image so much easier!  The tools I have this year are so much more powerful than the ones I had last year.

Camera geek info:

  • Williams Optics Zenith Star 73 III APO telescope
  • Williams Optics Flat 73A
  • ZWO 2” Electronic Filter Wheel
  • Antila LRGB filters
  • ZWO ASI183MM-Pro-Mono camera
  • ZWO ASiair Plus
  • iOptron CEM40
  • Dell City, Texas Bortle 2-3 dark skies

Frames:

  • February 13, 2024
    • Interleaved LRGB lights
      • 5 60 second Gain 150 L lights (only used for the comet)
      • 5 60 second Gain 150 R lights
      • 5 60 second Gain 150 G lights
      • 4 60 second Gain 150 B lights
    • 30 0.05 second LRGB flats
    • 30 0.05 second darks
    • 30 60 second darks

Processing geek info:

  • PixInsight
  • BlurXterminator
  • NoiseXterminator
  • StarXTerminator
  • ImageBlend

Comet vs Clouds: A Glimpse of Comet Tsuchinshan-ATLAS C/2023 A3

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On Sunday morning, we got up at 4:00 AM to drive to a spot with a long view to the East to go comet hunting.  I successfully got the telescope set up prior to the time when Comet Tsuchinshan-ATLAS C/2023 A3 was supposed to rise.  However, when the comet did rise, the ASIAIR could find stars, but couldn’t plate solve to figure out if it was pointing exactly right.  So I ended up starting imaging without having successfully scanned to the predicted comet location.  Since I could see a tiny comet in the first shot, I let the system take an automated sequence of shots.  60 second shots were too bright, so I started with 10 second shots, and when they became too bright, I switched to 1 second shots.

I also tried taking pictures with an 85 mm lens on my Canon EOS 60D, but that didn’t pick up the comet at all.  What it did pick up was the reason I didn’t get very many good comet images … clouds!  Of course, clouds are terrible for astrophotography, but they do lead to nice sunrise pictures.

We stayed for the sunrise, went out to breakfast, and then headed home.

Astrophotography is really two hobbies: capturing the images and processing them.

When we got home, I worked on processing the images I’d gotten.  I could see the comet in the 10 second images and in the 1 second images, but the 1 second image ones were generally partially through the clouds.  So I ended up using only the 10 second images.  Because there weren’t any stars captured in these short images, I only needed to process for the comet and use Comet Alignment to align the frames.

I’m hoping that I’ll get some better images later this fall.  Are you making plans to try to see this one?

Camera geek info:

  • Williams Optics Zenith Star 73 III APO telescope
  • Williams Optics Flat 73A
  • ZWO 2” Electronic Filter Wheel
  • Antila RGB filters
  • ZWO ASI183MM-Pro-Mono camera
  • ZWO ASiair Plus
  • iOptron CEM40
  • Bacliff, Texas Bortle 6 suburban skies

Frames:

  • 4 10 second red lights
  • 7 10 second green lights
  • 5 10 second blue lights
  • 30 0.02 second flats for green and blue
  • 30 0.05 second flats for red
  • 30 0.02 second flat darks for green and blue
  • 30 0.05 second flats darks for red
  • 1 second dark from library 

Processing geek info:

  • PixInsight
  • Generalized Hyperbolic Stretch
  • NoiseXterminator

M27 NGC6853 The Dumbbell Nebula or The Apple Core Nebula

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M27, also called the Dumbbell Nebula or Apple Core Nebula, is a planetary nebula – the gases expelled from a red giant star before it becomes a white dwarf, lit up by that star.  It’s located in the Milky Way, approximately 1250 light years away, and it has an apparent size of 8 arcmintues, making it 2.9 light years across.  It’s estimated to be 12,700 years old.

Planetary nebulae do not last long on an astronomy time scale because the expelled gases grow dimmer as they expand away from the central star.  I am glad I live in a time when we can observe them and they can be observed!

Planetary nebulae were originally called that because they looked like a round (like a planet) ball of fuzz by visual observers.  However, now we know they have nothing to do with planets and are actually shell(s) of gas expelled from a red giant star.  With astrophotography, we can pick up so much more detail than a fuzzball, and so we end up with interesting names.  For this nebula, some thought the inner core of this nebula looked like a dumbbell; others thought it looked like an apple core.  With the outer fringe, what do you think it looks like?

I used data from my driveway in Friendswood, Texas with suburban Bortle 7 – 8 brightness skies (lots of light pollution) to make this image.  In order to capture the outer fringe I needed a lot of data: 12.2 hours of Ha data and 10.65 hours of Oiii data, taken over nine nights.

This is a narrowband image, mapping Oiii to blue and Ha to red.  My goal was to capture both the details in the core and the outer fringe.  It took three processing tries, but I think I was ultimately successful.

Isn’t our galaxy beautiful?

Camera geek info – Narrowband:

  • Williams Optics Zenith Star 73 III APO telescope
  • Williams Optics Flat 73A
  • ZWO 2” Electronic Filter Wheel
  • Antila HO filters
  • ZWO ASI183MM-Pro-Mono camera
  • ZWO ASiair Plus
  • iOptron CEM40
  • Friendswood, Texas Bortle 7-8 suburban skies

Frames:

  • June 22, 2024
    • 20 60 second Gain 150 Ha lights
    • 30 0.05 second Gain 150 Ha flats
  • June 28, 2024
    • 47 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • July 3, 2024
    • 100 60 second Gain 150 Ha lights
    • 30 0.05 second Gain 150 Ha flats
  • August 15, 2024
    • 256 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • August 16, 2024
    • 283 60 second Gain 150 Ha lights
    • 30 0.05 second Gain 150 Ha flats
  • August 20, 2024
    • 45 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • August 22, 2024
    • 136 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • August 23, 2024
    • 155 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • August 24, 2024
    • 327 60 second Gain 150 Ha lights
    • 30 0.05 second Gain 150 Ha flats
  • 30 Flat Darks from library
  • 30 Darks from library

Processing geek info:

  • PixInsight
  • BlurXterminator
  • NoiseXterminator
  • StarXTerminator
  • Generalized Hyperbolic Stretch
  • NBColourMapper

NGC6357 The Lobster Nebula or the Bug-Eyed Monster Nebula

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NGC6357, the Lobster Nebula, is an emission nebula.  It is a large star-forming region containing three star clusters, many young stars, and some massive stars.  One cluster is Pismis 24, located just above the bright blue core in this picture.  The stars in this cluster are about 1 million years old and four are massive – 40 – 120x the mass of our sun, among the most massive stars in our galaxy.  The Lobster Nebula is located in the Milky Way, approximately 5550 light years away, and it has an apparent size of 60 x 45 arc min, so it is approximately 97 x 73 light years across.    

From my driveway, the Lobster Nebula is low to the South and is only visible for a short time from when it rises above my house to when it goes behind the pine tree.  So it took many nights of data collection to get enough data to make this image – 12.2 hours of data collected over 13 nights.  And it would still benefit from more!  I may collect more data the next time we visit the dark skies of Dell City, Texas, where I have an unimpeded view to the South.  But, until then, I have declared the end of Lobster season!

Although NGC6357 is traditionally named the Lobster Nebula, I think it looks like a bug-eyed monster.  And a bug-eyed monster should be green with a red core and have red eyes.  So in addition to the traditional Hubble SHO (Sii mapped to red, Ha to green, and Oiii to blue), I also made a version using a OHS (Oiii mapped to red, Ha to green, and Sii to blue) palette.  I thought this version produced a nice contrast in the pillar in the core near the Pismis 24 cluster.

Which color palette do you like better?

Camera geek info – Narrowband:

  • Williams Optics Zenith Star 73 III APO telescope
  • Williams Optics Flat 73A
  • ZWO 2” Electronic Filter Wheel
  • Antila SHO filters
  • ZWO ASI183MM-Pro-Mono camera
  • ZWO ASiair Plus
  • iOptron CEM40
  • Friendswood, Texas Bortle 7-8 suburban skies

Frames:

  • June 7, 2024
    • 106 60 second Gain 150 Ha lights
    • 30 0.05 second Gain 150 Ha flats
  • June 8, 2024
    • 51 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • June 13, 2024
    • 73 60 second Gain 150 Sii lights
    • 30 0.05 second Gain 150 Sii flats
  • June 14, 2024
    • 82 60 second Gain 150 Sii lights
    • 30 0.05 second Gain 150 Sii flats
  • June 15, 2024
    • 81 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • June 28, 2024
    • 69 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • June 29, 2024
    • 37 60 second Gain 150 Sii lights
    • 30 0.05 second Gain 150 Sii flats
  • July 3, 2024
    • 51 60 second Gain 150 Ha lights
    • 30 0.05 second Gain 150 Ha flats
  • August 6, 2024
    • 13 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • August 8, 2024
    • 61 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • August 6, 2024
    • 37 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • August 6, 2024
    • 34 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • August 6, 2024
    • 36 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
  • 30 Flat Darks from library
  • 30 Darks from library

Processing geek info:

  • PixInsight
  • BlurXterminator
  • NoiseXterminator
  • StarXTerminator
  • Generalized Hyperbolic Stretch
  • NBColourMapper

M17 “The Blue Swan with a Golden Egg” – Spotting the Swan and Narrowband Processing Notes

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I call this image The Blue Swan with the Golden Egg.  Can you see the blue swan sitting on a purple nest with a golden egg?

M17 is an emission nebula with many names, including the Swan Nebula.  When I saw the Oiii narrowband images, I finally understood why it is called the Swan Nebula, and I’ve oriented this image so that the swan is “floating” with its head up.  If you see the two dark spots near the center of the frame and the brightest part of the nebula, the lower one is the swan’s neck.  The largest portion of the bright part of the nebula is the swan’s body, the neck comes up past the dark spot, and then the head is above it.  I’ve included a single frame, below, where it the swan is more obvious because the rest of the nebulosity is hidden, and I’ve sketched in the swan on top of it.  Howard Banich has some lovely hand-drawn sketches of this nebula in a Sky & Telescope article. 

M17 is a large star-forming region.  It’s been the home for three star-forming events, but the stars created are mostly hidden behind the molecular cloud.  The massive stars it made emit UV radiation that excites the hydrogen gas to form the emission nebula.  It’s located in the Milky Way, approximately 5500 light years away, and the brightest portion has an apparent size of 10 arc min, so it is approximately 15 light years across.  The region of gas around it is larger, with an apparent size of about 30 arc min, so it is approximately 48 light years across.  

I have learned a lot about narrowband processing while working on this image, and I’ve gotten a lot of useful pointers from the folks at the astrobin forums.

I initially made four different color maps using NBColourMapper, with the following color assignments and results:

Palette NameNaturalHubble (SHO)Canada France Hawaii Telescope (HOS)Extra
H-alpha color mappingRed (0)Green (120)Red (0)Red (0)
Oiii color mappingTurquoise (180)Blue (240)Green (120)Blue (240)
Sii color mappingOrange (20)Red (0)Blue (240)Green (120)
ResultMostly red, not much color contrastBlue Swan with Green/Yellow nebula, more color contrastYellow Swan with Pink/Purple Nebula, more color contrastPink/Purple Swan with Yellow/Purple nebula, more color contrast

My Hubble SHO pallet was extremely green and looked nothing like the classic Hubble images which tend to be very blue and yellow/red.  Apparently mostly green images are not considered attractive (it’s not easy being green) and don’t have the desired contrast.  After getting feedback on the astrobin forum and watching a lot of videos, I learned that the general technique for narrowband color mapping is to first normalize the images using LinearFit so the different bands are all equally bright.  This loses the relative signal strengths of the different bands, but means that the dimmer bands aren’t overwhelmed by the stronger ones.  

After color mapping the three linear fit data sets and running NBColourMapper, I used Dynamic Background Extraction to remove the background color bias.  I liked what it did with the background more than Background Neutralization, which I also tried.  

For color calibration, I tried using SPCC in narrowband mode.  This seemed to want to push the nebula back to the original colors – very green for SHO and red and gold for HOS (which I actually liked).  This makes sense, but I didn’t end up using the resulting images.  I tried using ColorCalibration.  This brought out the reds and golds in the SHO image, but it ended up with extreme colors in the nebula.

I got more astrobin advice and watched some Adam Block videos.  Not only does Adam provide excellent explanations of the effects of various tool settings (the “why” as well as the “what”), but he also talks about his image processing philosophy, which in this case was eye-opening for me.  He shared his philosophy of thinking about how he wanted the image to look when it was done before he started processing it which I found extremely useful.  He gave me a different and better way to think about narrowband astrophotography image processing.  I looked at my original narrowband data and decided what I’d like to try to do is bring out the details that are in the Sii data.  Following a similar philosophy to what he did in his example, I used PixelMath to map the narrowband data to RGB, emphasizing the red and the blue and dialing back the blue and the green when there was red to emphasize the red Sii details with the following settings:

  • R = 2*S
  • G = 0.4*H+0.6*H*(1-S)
  • B = O+2*(1-S)*O

I finally achieved the blue I’d been looking for!

After narrowband mapping, I stretched the nebula using ScreenTransferFunction and the HistogramTransformation, then used a new to me tool, High Dynamic Range Multiscale Transform (HDRMT), which “flattened” the image so that I could see details in both the nebula core and in the surrounding faint nebula.  I finished by using Curves, working on the c curve to emphasize the reds a little more (after the PixelMath mapping, I didn’t need to do much in Curves).  

With this color mapping, the stars turn out over-blue.  I processed them separately and converted them to be only white, then added them back in.

This has taken me a couple of weeks of learning and experimenting, and I think it was worth it.  I ended up with an image that makes me think “isn’t the universe beautiful?”

Camera geek info – Narrowband:

  • Williams Optics Zenith Star 73 III APO telescope
  • Williams Optics Flat 73A
  • ZWO 2” Electronic Filter Wheel
  • Antila SHO filters
  • ZWO ASI183MM-Pro-Mono camera
  • ZWO ASiair Plus
  • iOptron CEM40
  • Friendswood, Texas Bortle 7-8 suburban skies

Frames:

  • June 8, 2024
    • 58 60 second Gain 150 Ha lights
    • 30 0.05 second Gain 150 Ha flats
    • 17 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
    • 30 0.05 second Gain 150 flat darks
    • 30 60 second darks
  • June 14, 2024
    • 28 60 second Gain 150 Sii lights
    • 30 0.05 second Gain 150 Oiii flats
    • 30 0.05 second Gain 150 flat darks
  • June 15, 2024
    • 77 0.05 second Gain 150 Sii lights
    • 30 0.05 second Gain 150 Sii flats
  • June 16, 2024
    • 85 60 second Gain 150 Oiii lights
    • 30 0.05 second Gain 150 Oiii flats
    • 30 0.05 second flat darks

Processing geek info:

  • PixInsight
  • BlurXterminator
  • NoiseXterminator
  • StarXTerminator