Although it was included in the Sharpless Catalogue of Hii regions, it is actually a very dim planetary nebula. It is located at a distance of 711 light years from the Solar System in the constellation, Cassiopeia. Based upon its expansion rate it is thought to be about 7500 years old.
Planetary nebulae are formed when a star dies of “old age” and expels ionized shells of gas. The nebula is nearly circular in shape. It is much brighter to the southeast (lower right) because the central star is moving rapidly in that direction. Faint wisps of gas can also be seen in the opposite direction.
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. It moves about 300,000 miles per hour. It is also going through layers of the interstellar medium. This impacts the shape of the nebula and makes it asymmetrical. The bright part of the nebula is the bow shock. It occurs as a fast-moving planetary nebula interacts with the interstellar medium.
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. This is particularly true if you are not observing from a very dark site far from light pollution. For imaging, a long focal length telescope on an equatorial mount is very helpful. And then a lot of exposure is required to bring out this dim PN.
APT is controlling the imaging sessions. This image represents about 20 hours of exposure. It uses a GSO RC8 at 1625mm fl and a ZWO ASI071MC camera. The setup is atop a Skywatcher EQ6r Pro mount. The Antlia quad-band light pollution filter was used in my bortle 4 sky.
