Sharpless 308, commonly known as the Dolphin Head Nebula, is a huge cosmic bubble located near the center of the constellation Canis Major, a few degrees south of Sirius, the brightest star in the night sky. Located about 5,000 light-years away, it covers over 2/3 degrees in the sky (1.5 times the size of the full Moon) which corresponds to a diameter of 60 light-years at its estimated distance. The nebula surrounds the Wolf-Rayet star EZ Canis Majoris, the bright blue star near the bubble's center, which is thought to have over 20 times the mass of the Sun and is in a short pre-supernova evolutionary stage.
Its outer shell of hydrogen gas has been used up, revealing inner layers of heavier elements that burn at ferocious temperatures. The intense radiation pouring out from EZ Canis Majoris forms stellar winds that whip up nearby material, sculpting and blowing it outwards. These processes have moulded the surrounding gas into a vast bubble. The fringes of these bubbles are nebulous and wispy, as can be seen in this image. The small "soap bubble" visible at the base of the dolphin head is a planetary nabula named G234.9-09.7 and was discovered less than 20 years ago.
I am particularly fond of this object because I contributed to popularize it by making
one of the first color images combining RGB and narrowband back in 2011, image then taken up in many forums and publications, all at a time when SH 308 was largerly unknown to the amateur community with almost no images of it.
Image taken at the AMT observatory I set and manage with Andy Lau and Tommy Tse in Chile (hosted by Obstech)
Takahashi CCA250 (250/f5) - ZWO 6200MM Ha (615m) - OIII (735m) R (60m) G (60m) B (60m)
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