Changes

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]].<ref name=apod/> 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 '''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]].<ref name=apod/> 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 year]]s away and lies on the boundary of the Cepheus B molecular cloud.<ref>{{cite web|url=https://apod.nasa.gov/apod/ap181114.html|title=The Cave Nebula in Hydrogen, Oxygen, and Sulfur|accessdate=2019-10-17|publisher=apod.nasa.gov|date=2018-11-04}}</ref> THe nebula is thought to be around 35 light years in radius.<ref name=annesastronomynews>{{cite web|url=http://annesastronomynews.com/photo-gallery-ii/nebulae-clouds/the-cave-nebula-sh2-155-by-adam-block/|title=The Cave Nebula, an emission nebula in Cepheus|accessdate=2019-10-17|publisher=annesastronomynews.com}}</ref> The bright ridges of the nebula are illuminated by the light generated by two [[star]]s, designated HD 217061 and HD 217086.<ref name=annesastronomynews/> These are located in the Cepheus B cloud and their light [[ionization|ionizes]] [[hydrogen]] [[molecules]] to be doubly ionized.<ref>{{cite web|url=https://futurism.com/astronomy-photo-of-the-day-92213-the-cave-nebula-sh2-155-2|title=Astronomy Photo of the Day – 9/22/13: The Cave Nebula (SH2-155)|accessdate=2019-10-17|publisher=futurism.com|date=2013-09-22}}</ref> Infrared images of the nebula taken by the [[Spitzer Space Telescope]] have revealed a [[star cluster|cluster of stars]] within the nebula.<ref>{{cite web|url=https://science.nasa.gov/cave-nebula-infrared-spitzer|title=The Cave Nebula in Infrared from Spitzer|accessdate=2019-10-17|publisher=science.nasa.gov|date=2019-06-11}}</ref>

The nebula is found roughly 2,400 [[light year]]s away and lies on the boundary of the Cepheus B molecular cloud.<ref>{{cite web|url=https://apod.nasa.gov/apod/ap181114.html|title=The Cave Nebula in Hydrogen, Oxygen, and Sulfur|accessdate=2019-10-17|publisher=apod.nasa.gov|date=2018-11-04}}</ref> The nebula is thought to be around 35 light years in radius.<ref name=annesastronomynews>{{cite web|url=http://annesastronomynews.com/photo-gallery-ii/nebulae-clouds/the-cave-nebula-sh2-155-by-adam-block/|title=The Cave Nebula, an emission nebula in Cepheus|accessdate=2019-10-17|publisher=annesastronomynews.com}}</ref> The bright ridges of the nebula are illuminated by the light generated by two [[star]]s, designated HD 217061 and HD 217086.<ref name=annesastronomynews/> These are located in the Cepheus B cloud and their light [[ionization|ionizes]] [[hydrogen]] [[molecules]] to be doubly ionized.<ref>{{cite web|url=https://futurism.com/astronomy-photo-of-the-day-92213-the-cave-nebula-sh2-155-2|title=Astronomy Photo of the Day – 9/22/13: The Cave Nebula (SH2-155)|accessdate=2019-10-17|publisher=futurism.com|date=2013-09-22}}</ref> Infrared images of the nebula taken by the [[Spitzer Space Telescope]] have revealed a [[star cluster|cluster of stars]] within the nebula.<ref>{{cite web|url=https://science.nasa.gov/cave-nebula-infrared-spitzer|title=The Cave Nebula in Infrared from Spitzer|accessdate=2019-10-17|publisher=science.nasa.gov|date=2019-06-11}}</ref>

==References==

==References==