Sh2-155, as designated in the Sharpless Catalog of HII regions, is commonly referred to as the Cave Nebula. It is a diffuse nebula located in the constellation of Cepheus the King. The distance to the nebula is estimated to be approximately 2,400 light-years from the Earth. The Cave Nebula is an active stellar nursery where new stars are currently being born. The radiation and stellar wind from the hot blue O-type star, HD 217086, located just above the center of the image is thought to be the trigger for this new generation of stellar formation. Studies conducted by the Chandra X-ray Observatory and the Spitzer Space Telescope support this stellar formation conclusion.
The image above was compiled from narrow band filtered exposures to create a mapped color depiction of the nebula. The standard Hubble pallet of SII mapped to red, Ha mapped to green, and OIII mapped to blue was utilized for the image. The stars were overlaid with data from a Near True Color (Ha/OIII/OIII) image.
A Near True Color image of Sh2-155 may be viewed here.