Sharpless 2-155 - Cave Nebula

The Cave Nebula is a faint region of Hydrogen-α emission and surrounding dust in the constellation Cepheus. It is a dim and very diffuse bright nebula within a larger nebula complex containing emission, reflection, and dark nebulosity.

Visually it is a difficult object, but with adequate exposures, it makes a striking image. The nebula gets its name from the dark lane at the eastern side that has the appearance of a deep cave. This area is rich in detail, which is especially prominent when imaging in Hα light. In addition to the central "cave-like" structure, notice the subtle patch of blue reflection nebulosity in the upper right hand portion of the field.

The Cave Nebula lies about 2400 light years away, and has a physical diameter of about 70 light years. This corresponds to apparent dimensions of about 50 by 30 arc minutes.