SH2-155

Sh2-155 (also designated Caldwell 9, Sharpless 155 or S155) is a diffuse nebula in the constellation Cepheus within a larger nebula complex containing emission, reflection, and dark nebulosity. It is widely known as the Cave Nebula, though that name was applied earlier to Ced 201, a different nebula in Cepheus. Sh2-155 is an ionised H II region with ongoing star formation activity, at an estimated distance of 2400 light-years from Earth.