Sh2-174 or PK 120+18.1 is an enigmatic object. The designations of a catalog of emission nebulae (Sh2) and a catalog of planetary nebulae (PK) already indicate that the classification of this object is unclear.Sh2-174 is very small, but very tall – it’s about 20′ in diameter. The object was first noticed by Stewart Sharpless, who discovered the Red Nebula consisting of ionized hydrogen on photographic plates. But also on photos in the light of double ionized oxygen (OIII) one could recognize something. This led to the conclusion or hypothesis that it could also be an ancient planetary nebula. But there was no white dwarf as the central star.
