Updated: Sep 29, 2020
Sh2-188 is a planetary nebula in Cassiopeia. It does not have an official name but is often called the "Shrimp Nebula" or even the "Dolphin Nebula" due to its shape.
Object Designation: Sh2-188
Also known as: The Shrimp Nebula
Object Type: Planetary Nebula
Distance: 850 light-years away
Discovered in: 1951
Sharpless-188 is small but really pretty object. It is dim and a difficult target for beginner astrophotographers. The best way to photograph it is by using narrowband filters (Hydrogen Alpha, Sulfur II and Oxygen III) and do long exposures. Sh2-188 was discovered in 1951 but really confirmed through the fantastic art of Astrophotography in the year 1965. It was first believed to be a supernova remnant mostly because of the "Crescent-like" shape.
Like we said earlier, Sharpless-188 is a planetary nebula. Planetary nebulae are formed when a star dies of “old age” and expels ionized shells of gas. The object itself is pretty young compared to most similar DSO’s and is only 22,500 years old.
Planetary nebulae are usually symmetrical in shape, but that isn’t the case of Sh2-188. The Shrimp Nebula is believed to travel through space at an incredible rate (about 300,000 miles per hour) and to be going through layers of the interstellar medium. This impacts the shape of the nebula and makes it asymmetrical.
Like our recent picture of the Cave Nebula, this is probably just a work in progress image because some of the data was shot through the California Wildfires' haze and I do not feel proud of the result, especially knowing it is 37 hours of total exposure!
Below is our result. The Oxygen and Sulfur data were both shot through the smoke and looked terrible. The object itself seemed to shine easily through the haze but the overall frames were very noisy.
Sh2-188 from our Bortle 9 backyard in narrowband
Camera: ZWO ASI 1600MM
Telescope: Stellarvue SVX130
Mount: Paramount MyT
Guiding: ZWO ASI 290MM Mini
Accessories: Moonlite Nightcrawler focuser
Total Exposure Time: 37 hours and 45 minutes
Exposure Time per frame: 10 minutes
Filters: Chroma 3nm Ha/Sii/Oiii
How to find Sh2-188?
The Shrimp Nebula is not bright enough to be seen with the naked eye or binoculars. Its small size doesn't help either. It is also very difficult to see with a telescope, especially if you are not observing from a very dark site far from light pollution.
Finding Sh2-188 is not too difficult. It is located in one of the most obvious constellations in the night sky, Cassiopeia. It also stays high in the sky for several months! To locate it, look for the second bright star in Cassiopiea's "W" shape. The nebula can be found just South of that star.
Processing of the Shrimp Nebula
Processing Sh2-188 was honestly very difficult. I don't want to blame the smoke for everything, but I am hoping it was the reason for how tough it was to process this data. The background looked terrible, mostly from the OIII and SII channels, and it was difficult to keep the target crisp while trying to fix the noise all around. I went through my usual PixInsight workflow, and I believe that is the best I could do to process this image.
I wonder if it would have been a good idea to apply a much tighter crop and process the object without so much of the background around it.
If you are interested in learning how I process all our images, you can download a full PDF "follow along" file that contains 75 pages, a full 1 hour and 45 minutes walkthrough tutorial video and even raw data HERE.
What did each narrowband channel look like?
Below you can see what each stacked frames looks like for the three narrowband channels. We used the following filters to capture Sh2-188:
Hydrogen Alpha (left)
Sulfur II (center)
Oxygen III (right) - Taken through thin layers of smoke from the California Wildfires
Sh2-188 was a tough target. It is small, very faint, and difficult to process. The smoke from the California wildfires definitely did not help and we cannot wait for it all to be over so that we can revisit this target.
We chose not to make this image available as a print because it does not meet our quality standards, but check out the prints we have for other images HERE!
Have you captured the Shrimp Nebula? Attach your image in the comments and let us know your acquisition details!
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