The Cave Nebula

The "Cave Nebula", in the centre of this image, is a popular name for Sh2-155, an emission nebula in the constellation Cepheus. It appears cave-like due to a dark, hollowed-out area surrounded by a bright, ionized gas rim, which is an active star-forming region (H II region). Located approximately 2,400 to 3,000 light-years away, it is part of a larger star-forming complex called Cepheus B.

The blue area of nebulosity to the upper left of the cave is the reflection nebula vdb155.