Sh2-174 is an unusual, ancient planetary nebula in Cepheus. Planetary nebulae form when a low-mass star sheds its outer layers at the end of its life, leaving a hot white dwarf that ionizes the ejected gas. In most cases the white dwarf lies near the geometric center of the nebula.
In Sh2-174, however, the white dwarf (GD 561) is clearly offset to the right within the bluish ionized shell. The displacement and the brightened rim are understood as the result of interaction with the surrounding interstellar medium: as the star and its shell move through space, ram pressure sculpts a bow-shock–like leading edge and pushes the visible envelope downstream.
This image has been captured from the Curiosity Observatory in Àger, Catalonia, under a B3 sky. I used 51 hours of imaging time combining LRGB filters for broadband, and Ha + OIII in narrowband.