What is an Emission Nebula?

An emission nebula is a luminous cloud of interstellar gas due to the ionization of its atoms through ultraviolet radiation. Among locations in which emission nebulae are found, H II regions and planetary nebulae are the most prominent. H II being an area in which a recent star formation has taken place emitting UV light that ionizes the gas that surrounds it, and the latter being a dying star that has ejected its outer layers with it’s exposed core ionizing them.