|Right ascension||22h 57m 05.9s|
|Declination||+62° 38′ 09″|
|Type of object||Diffuse nebula|
|Distance from Earth||2,400 ly|
The Cave nebula (Sh2-155, Caldwell 9) is a Diffuse nebula in the constellation of Cepheus and can be seen in the plane of the Milky Way. There are many nebulae situated in this patch of sky including the Elephant's Trunk nebula and the Bubble nebula. The nebula is quite dim and diffuse and this, along with being surrounded by dust, makes it difficult to observe.
The nebula is found roughly 2,400 light years away and lies on the boundary of the Cepheus B molecular cloud. THe nebula is thought to be around 35 light years in radius. The bright ridges of the nebula are illuminated by the light generated by two stars, designated HD 217061 and HD 217086. These are located in the Cepheus B cloud and their light ionizes hydrogen molecules to be doubly ionized. Infrared images of the nebula taken by the Spitzer Space Telescope have revealed a cluster of stars within the nebula.
- Sh2-155. Simbad Astronomical Database. simbad.u-strasbg.fr. Retrieved on 2019-10-17.
- SH2-155: The Cave Nebula. apod.nasa.gov (2017-03-23). Retrieved on 2019-10-17.
- The Cave Nebula in Hydrogen, Oxygen, and Sulfur. apod.nasa.gov (2018-11-04). Retrieved on 2019-10-17.
- The Cave Nebula, an emission nebula in Cepheus. annesastronomynews.com. Retrieved on 2019-10-17.
- Astronomy Photo of the Day – 9/22/13: The Cave Nebula (SH2-155). futurism.com (2013-09-22). Retrieved on 2019-10-17.
- The Cave Nebula in Infrared from Spitzer. science.nasa.gov (2019-06-11). Retrieved on 2019-10-17.