NGC 2359 – Thor’s Helmet

Thor’s Helmet (NGC 2359 or SH2-208) is an emission nebula in Canis Major located 12 thousand light years away. At the center of the round bubble is a Wolf-Rayet star, that is thought to be at the early stages of a supernova. This is similar to what is happening in the Bubble Nebula. The Wolf-Rayet type star is what is making this nebula shine.

As the winter of 2020-2021 has been extremely cloudy, this image was taken over the span of many months. Also, most nebula shine much brighter in the hydrogen-alpha range, but this one is extremely strong in the Oxygen-III, which is the reason why the nebula appears so blue in this image.

Imaging Details

  • Workflow: Narrowband
  • Hydrogen-Alpha Filter: 30*600 seconds
  • Oxygen-III Filter: 30*600 seconds
  • Binning: 1×1
  • Total Imaging Time: 10 hours
  • Imaging Dates (5 nights):
    • 11/13/2020
    • 11/21/2020
    • 1/21/2021
    • 3/5/2021
    • 3/6/2021

Starless Image

I also decided to try Thor’s Helmet in a starless mode following the star removal process. For this application, I kept a few of the largest/brightest stars in the image.

Thor’s Helmet Imaging Notes

Thor’s Helmet was not an easy target to image, especially for my latitude. Thor’s Helmet is very low on the southern horizon, limiting my imaging window. Plus, because it is so low in the sky, I’m imaging through more atmosphere than if it were higher, which impacts that amount of signal I’m going to capture.

For anyone trying to image Thor’s Helmet, a few suggestions

  1. There is a very strong OIII signal with Thor’s Helmet. I didn’t realize this when I started imaging, so I probably wasted too much time acquiring through the OIII filter
  2. The HA signal is fairly weak, which is surprising as most emission nebula are usually strong in HA. Knowing this, I would have opted to capture 2X more HA than OIII images.
  3. The SII signal is pretty much non-existent. I captured 5 images at 600 seconds and was not able to see any nebula signal, so I stopped spending time with SII. With really dark skies, there might be some signal, but very minimal and would require a lot of time to capture.