This object is an emission nebula in the constellation Cassiopeia, approximately
7500 light years from earth. It bears a striking resemblance to the Rosette Nebula
in the constellation Monoceros, though Sharpless 170 is less than half the size
(thus I think it should be called "The Little Rosette"; maybe if the name catches
on, this beautiful object will get a little more of the attention it deserves).
For an idea of scale, this nebula appears about 2/3 the size of the full moon in the sky.

This image was published in "Sky & Telescope" August 2016 (page 75).

Image data:
Camera: SBIG STL-11000
Exposure: 10 1/2 hours (7 hours Hydrodgen-alpha; RGB 70 minutes each)
Telescope: Hyperion 12.5"