NGC 2359, also called Thor’s Helmet, is an emission nebula – in this case a planetary nebula of ionized gas around a hot central star, Wolf-Rayet WR7.  WR7 is a massive star which has shed matter, and then its stellar wind has blown and compressed that matter into a bubble, and its UV radiation has ionized it to make the beautiful nebula we see.  This planetary nebula has a very complex shape, likely due to interactions with a nearby molecular cloud.  It’s located in the Milky Way, approximately 12,900 light years away, and it’s approximately 30 light years across, giving it an apparent size of 16 x 8 arc min.

In our early 2024 trip to the fantastic dark skies of Dell City, Texas, I took the images used to make the picture above using two narrow band filters – H-alpha (assigned to red) and Oiii (assigned to blue).  These color assignments are close to, but not exactly, true to color.

In our early 2023 trip to the fantastic dark skies of Dell City, Texas, I used a DSLR to make an RGB image of the nebula.  When I processed it last year, I hadn’t learned many of the processing techniques I use today, so I decided to reprocess it.  I was absolutely amazed at the difference processing can make (try the slider bar to see the difference!).  

I love both the narrowband version and the new RGB version.  Which 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
• Dell City, Texas Bortle 2-3 dark skies

Frames:

• February 13, 2024
  • HO lights
    • 45 120 second Gain 150 Ha lights
    • 35 120 second Gain 150 Oiii lights
  • 30 0.05 second Gain 150 H flats
  • 29 0.05 second Gain 150 O flats
  • 30 0.05 second flat darks
  • 30 120 second darks

Processing geek info:

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

Camera geek info – RGB:

• Canon EOS 60D in manual mode, 179 second exposure, ISO 2000, custom white balance 3500K
• Williams Optics Zenith Star 73 III APO telescope
• Williams Optics Flat 73A
• iOptron CEM40
• Dell City, Texas Bortle 2-3 dark skies

Frames:

• 64 3 minute lights
• 20 3 minute darks
• 40 0.1 second flats
• 40 0.1 second flat darks

Processing geek info – RGB:

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