About The Triangulum Galaxy

The Triangulum Galaxy, also known as Messier 33 or M33, is a spiral galaxy located approximately 3 million light-years from Earth in the constellation Triangulum. It is one of the closest galaxies to the Milky Way and the Andromeda Galaxy.

The Triangulum Galaxy is classified as a type “Sc” spiral galaxy, which means it has loosely-wound arms and a relatively small central bulge. It is smaller and less massive than the Milky Way and Andromeda galaxies, with an estimated diameter of around 50,000 light years.

The Triangulum Galaxy is estimated to be about 12-14 billion years old, making it one of the oldest galaxies in the universe. Throughout its history, it has undergone several periods of star formation, resulting in a population of young, hot blue stars and older, cooler red stars.

The Hydrogen-alpha emission (deep red spots as seen in this photo) in the Triangulum Galaxy has revealed numerous star-forming regions, including massive stellar nurseries and giant H-II regions where young stars are actively forming.

Capturing the Triangulum Galaxy

Overview

I set out to shoot this despite knowing better. I live in a heavily (Bortle 9) light-polluted suburb of New Jersey, only 14 miles from New York City, where nothing in the night sky can be seen with the unaided eye or even binoculars. In astrophotography, capturing broadband targets like galaxies in this environment is usually a no-go. I’m better off sticking with nebulas and narrowband targets that block most light pollution. That said, I am surprised at how well this came out.

The Triangulum Galaxy is one of the few galaxies in the night sky that does not require a monstrous telescope to capture. The only other galaxy that appears larger to our eyes is the Milky Way’s closest neighbor, the Andromeda Galaxy. Triangulum Galaxy’s size allows a medium-large refractor to perfectly capture this amazing night sky object.

Astrophotography Equipment: My Telescope, Camera, and Filters

I used my Astro-Tech AT115EDT telescope with the Astro-Tech .8x reducer, which gave me a focal length of 644mm and an aperture ratio of f5.6. I also used a ZWO ASI533MM mono camera and shot mostly LRGB using my Antlia LRGB-V filters. Lastly, I shot about three hours of integration time with a Hydrogen-Alpha (Ha) filter to bring out the red areas surrounding the galaxy. Without the addition of Hydrogen-Alpha, this image is extremely boring. The Ha is the icing on the cake.

Planning

My first step in my astrophotography process is to plan ahead in Telescopious. Telescopious is a website that allows you to enter information about your equipment, such as telescope focal length, reducers, camera sensor size, and camera image size and get a preview of your image. In this case, I entered my equipment, and Telescopious showed me a preview of what M33 would look like if I were to take it with that equipment.

M33 / Triangulum Galaxy on Telescopious.com
Triangulum Galaxy as seen on Telescopious with my Astro-Tech AT115EDT specs (644mm, .8x reducer) and ASI533MM (11.3 x 11.3 sensor)

Telescopious is extremely helpful for planning astrophotography projects, and I encourage everyone to use it. I personally donate monthly to it because I get so much use out of it.

Integration / Exposure Time

As with all my images, I used the ASIAir to capture roughly 14 hours of total exposure time outlined below:

Astrophotography FilterIntegration Time
Luminance5.75 hours
Red1.75 hours
Green2 hours
Blue1.75 hours
Ha3 hours
Total14.25 hours

Processing M33 Using Pixinsight

I processed this mainly in LRGB, as anybody would do with a galaxy. What makes this galaxy interesting, along with some other galaxies that also share this characteristic, is its spiral arms, which are made up of hydrogen-alpha.

Processing the LRGB channels

I shot roughly 11 hours of LRGB data. Below are the steps that I took in Pixinsight to do this. I have a Pixinsight Tutorial that you may want to watch, but that tutorial focuses on processing narrowband images, and this is a broadband image.

However, you will find that many of the steps below cross over and are part of the tutorial if you don’t know what they are. I’ve linked any process that has a tutorial video to it.

  1. Dynamic Crop to all final master files: L, R, G, B, and Ha |
  2. Dynamic Background Extraction to all final master files: L, R, G, B, and Ha
  3. Blur Xterminator (paid plugin) for Deconvolution on all master files: L, R, G, B, and Ha
  4. Noise Xterminator to remove noise from all master files: L, R, G, B, and Ha
  5. Create Your Enhanced Red Image (called NewRed) in which you add the Ha to the red channel. Because so much is involved in this step, I decided to break out that process below. See “Adding Hydrogen Alpha (Ha) to the Triangulum Galaxy” below.
  6. Combine NewRed (image you created from the step below), G, and B using Channel Combination to create a new RGB Image
  7. Use the Image Solver script to solve the image to prepare it for SpectroPhotoMetric Color Calibration
    • Note: You must have star databases installed to do this and the next step, SpectroPhotoMetric Color Calibration. This YouTube video from Peter Zelinka provides more information on how to do that.
  8. Use SpectroPhotoMetric Color Calibration to color calibrate it. Once the image solver script is completed, this should be fairly straightforward.
  9. SCNR to clear out any green cast you may have.
  10. Histogram Transformation: RGB Image
    • This usually requires multiple Histogram transformations. For this image, I did it six times. To learn how to do a Histogram transformation, please watch my tutorial.
  11. Histogram Transformation: Mono Luminance Image
  12. LRGBCombination: I add the luminance image to the RGB image in this step. In this video tutorial, I do this, but I use the Hydrogen-alpha image as the luminance. Don’t do that in this case! Use the luminance image.
  13. Star Xterminator (paid plugin) to remove all the stars from the image. This allows me to edit the image without damaging the stars.
  14. Intensity Transformations
    • Curves Transformation to adjust color
    • Curves Transformation to increase contrast
    • Curves Transformation to adjust the luminance
    • Curves Transformation to add saturation
    • Local Histogram Equalization to sharpen the image

Adding Hydrogen Alpha (Ha) to the Triagulum Galaxy

This process is intense and unique to spiral galaxies with hydrogen-alpha parts. The intense red fire-like dots of the hydrogen-alpha part may be what makes a galaxy stand out the most. See the picture of the Ha master below. This was made up of 60 Ha images that were 3 minutes in length each.

Hydrogen-alpha master image that will be combined with the red channel to make the Ha stand out more.
The master Ha image with 3 hours of data. I mixed this Ha image with the red image using the technique outlined below and then combined the new red, green, and blue to create an RGB image.

If you don’t feel like reading this, I’d encourage you to watch the video I watched from Paulyman Astro. I went to the spot in the video where you should start from, assuming you have the Red and Ha image ready.

I used his technique, which worked well. I’ll list the steps below if you don’t want to watch.

Before doing Step 4 above, you must add Ha to your red image to make the Ha in the galaxy’s dust lanes even more intense.

  • Create a duplicate of your red image and call it “NewRed”
  • Open up Pixelmath. You want to subtract some red from the Ha image but not all the red. To do this, use this Pixelmath formula:

Ha-0.25*NewRed

This formula will subtract 25% of the NewRed image from the Ha image. You can play around with that 25% (.25) value. In some cases, if your data is very good, you may need to use less.

Once you typed in the formula and made sure the variables are correct, click the “destination” bar in Pixelmath and choose to create a new image. Call the image “Ha_New”

Now we want to take the Ha_New image that was created and add it to the red image. However, we don’t want to add the noise from the Ha image too; the formula below will carry over just the Ha portions without the noise:

NewRed+(Ha_New-median(Ha_New))*1.2

This takes the duplicated red image (NewRed) and adds the new Ha image (Ha_New) to it without the noise, as you subtract the median. The median is the dark grayish area of the image where all the noise resides. There is also a multiplier at the end (*1.2), which you may need to play with to get the best results, but *1.2 worked for me.

You now have a finalized image called NewRed. You can return to step 4 above and use it in your channel combination. You should combine NewRed, G, and B.

In Conclusion

Galaxies with Ha in them may be one of Pixinsight’s more challenging projects. Although my image is still awesome, there’s room for improvement. If you have questions, please leave a comment below.

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