Anne Marie McComb's Sh2-308
Anne-Marie McComb has produced a fantastic demonstration of what extra time does for a faint image.
This emission nebula has a couple of different names, all of which are confusing. Officially, it’s known as Sharpless 2-308, but is known as the Dolphin Nebula. It really does look like a dolphin. Problem is, there’s another Dolphin Nebula out there, and that one is really hard to see from Australia.
This nebula is typical of those formed by Wolf-Rayet stars. At an early stage in their lives, these stars act like most others, shedding material outwards as they age. However, something causes these stars to suddenly blow gas out at a far faster rate, and the fast-moving gas catches up with the slow-moving gas from before. That’s what causes the bubble-shaped nebulas.
However, that’s not what Anne-Maree is trying to show. You’ll see that the two images here are similar, but one has far more of the dim details. This is all to do with signal-to-noise ratios. The longer exposure has more data and a better ratio, so she could tease out more dark details in processing.
You see, this nebula is a difficult one. It’s not only dim, but it only glows in some colours. Most nebulas are active in Hydrogen, which is a sort of pinkish colour. This one, not so much. Anne-Marie said that she wasn’t even sure it was there when she was looking through the Hydrogen filter. But when she switched to Oxygen, the nebula appeared.
Dim nebulas need lots of exposure time. This is a test of equipment, patience and technique. Anne-Marie's second photo is an integration of 7.5 hours of exposure, and you can see the difference it makes.
For the technical-minded, Anne-Marie uses a Sky-Watcher ED80 scope on an autoguided HEQ5 mount. She has an ASI1600MM pro camera behind Oxygen III and Hydrogen alpha filters. Hydrogen information is presented as red in the image, and the Oxygen is both blue and green.
Anne-Marie describes herself as a beginner, but judging by this image, she’s being harsh on herself.