Fun facts
Sh 2-308, also designated as Sharpless 308, RCW 11, or LBN 1052, and commonly known as the Dolphin Head Nebula, is an HII region located near the center of the constellation Canis Major, composed of ionized hydrogen. It is about 8 degrees south of Sirius, the brightest star in the night sky. The nebula is bubble-like and surrounds a Wolf–Rayet star named EZ Canis Majoris. This star is in the brief, pre-supernova phase of its stellar evolution. The nebula is about 4,530 light-years (1,389 parsecs) away from Earth, but some sources indicate that both the star and the nebula are up to 5,870 ly (1,800 pc) away. Yet others indicate the nebula is as close as 1,875 ly (575 pc) from Earth.
Sh 2-308 surrounds the central star Wolf–Rayet star EZ Canis Majoris, also designated EZ CMa or WR 6. Its apparent magnitude varies from 6.71 to 6.95. Its spectral type indicates that the star is very hot and luminous. The spectrum shows that it is devoid of hydrogen at the surface. EZ Canis Majoris is expected eventually to explode in a supernova, therefore subsuming the nebula.
The nebula was formed about 70,000 years ago by the star EZ Canis Majoris throwing off its outer hydrogen layers, revealing inner layers of heavier elements. Fast stellar winds, blowing at 1,700 km/s (3.8 million mph) from this star, create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of the star’s evolution. The hydrogen composing the nebula is ionized by intense ultraviolet radiation. The nebula is approximately 60 light-years across at its widest point.
The most favorable period for observing the nebula in the night sky is between the months of December and April. Its southern declination makes it easier to observe from the Southern Hemisphere, though it is easily visible from most of the Northern Hemisphere as well. It appears as a faint cloud in photographs taken with high-power amateur instruments, with the help of special filters.
Distance: 4530 light years
Radius: 30 light year
Apparent Dimensions: 35’ x 35’
Apparent Magnitude: 7.0
Constellation: Canis Major
Designations: Sh-308, RCW 11, LBN 1052
{ From: https://en.wikipedia.org/wiki/Sh_2-308 }
Capture & Processing Notes
We cancelled our Thanksgiving trip to Cincinnati because of Zeus – he had been bitten by a horsefly who, apparently, had deposited a worm into his paw. On Monday afternoon he started limping, by Monday night he could barely walk, and when I got up early on Tuesday morning to take him for a trail walk before leaving for DEN, we discovered the bloody paw – and we would not walk more than a few feet before sitting or laying down. After cancelling the Cincinnati trip, we briefly thought about driving down to Albuquerque on Friday-Saturday. But then rethought that, and decided that since it was still a holiday weekend it would be better to just stay home. I suggested a dark skies trip, since both Comanche and Kiowa National Grasslands had clear skies forecast – that idea was vetoed, we weren’t ready and it was still a holiday weekend, it would be better to stay home. So, I decided to set up Big Bertha and capture some data from the front patio, so as not to completely forego the clear nights of and surrounding the New Moon.
I started the night with CTB1 Garlic Nebula, while I waited for SH2-308 Dolphin Head Nebula to rise at about midnight. Collection on the Dolphin Head Nebula was rough because it is so low on the horizon – only visible for about four hours when it rises above 20°, only reaching a maximum of 30°. So the autoguider struggled with very poor performance so close to the equator. Also, even though I had auto meridian flip turned off – when I came out to do the meridian flip, it was already on the east side of the mount, but the sequence had failed to restart (likely because of the autoguider not reinitializing).
The primary objective of this imaging session, as with CTB1 Garlic Nebula’s a couple of weeks ago was to verify the framing of the object. I plan to image Dolphin Head Nebula during my trip to the Southern Hemisphere in March 2025 and the nebulosity is very faint in the SGP Framing & Mosaic Wizard image, so I wanted to make sure I had the framing correct before I spent a night of precious Southern Hemisphere dark skies on it.
I spent quite a bit of time processing the very noisy data set. Stacking in APP with Adaptive Airy Disc didn’t show much nebulosity, until the image was stretched by 30% – and then the noise is terrible! I re-stacked in APP with HaOIII Color, thinking that might be better, but it looked pretty much the same. I went through to fruition with the LR/PS processing – producing a hack-job image through creatinve tool application, masking, and blending. When I finished, I’d originally planned to quietly add the completed image and my notes to my journal and step away. But, then I decided – sometimes you have to admit, own, and share your failures!
So, here it is – a complete placeholder – the bad and the ugly SH2-308 Dolphin Head Nebula, with hopefully the good to come from imaging sessions in the Southern Hemisphere where it won’t be so close to the horizon (and I’ll be in dark skies).
The good news is that the “framing” experiment was successful in showing that the Dolphin Head Nebula is centered in the frame, which really was my primary objective of imaging this very low on the horizon object from the Bortle 6 front patio!
Sequence Plan (29Nov2024): Gain: 158, Temp: -0°C, offset=30. 45x300sec. Total: 225 minutes (3:45hrs). Captured 30Nov2024, 00:12MST – 04:37MST.
Processing summary: Captured in SGP, stacked in APP (Adaptive Airy Disc and HaOIII Color), star removal with Starnet++, processing with LR/PS
Equipment
Equipment: All equipment controlled by HP Probook running Sequence Generator Pro v4.4.1.1441.
- Imaging (ASI2400-BB-FF-LPro): ZWO ASI2400MC imaging camera on (Big Bertha) Orion 8″ f/8 Ritchey-Chretien Astrograph Telescope, Teleskop Service (TS) 2.5” Rack and Pinon Focuser M90, Teleskop Service Flattener 1.0x for RC Telescopes (TS-RCFLAT2), Optolong L-Pro LP filter
- Autofocuser: ZWO EAF Electronic Automatic Focuser – Standard (EAF-5V-STD)
- Mount: Rainbow Astro RST-300 (controlled by iHubo ASCOM driver)
- Polar alignment: QHYCCD camera (controlled by Polemaster for polar alignment)
- Autoguiding: Orion 60mm Multi-Use Guide Scope with Orion StarShoot AutoGuider Pro Mono Astrophotography Camera (controlled by PHD2)
Summary
Captured: 29 November 2024. Total data = 45 x 300 seconds, 225 minutes, 3:45 hours.
Shooting location: Colorado Springs, Colorado
Equipment: Big Bertha on Rainbow Astro RST-300
Processing summary: Captured in SGP, stacked in APP, star removal with Starnet++ v2, processing with LR/PS