An emission nebula is a type of interstellar cloud that glows due to the emission of light by excited atoms and molecules within the cloud. These nebulae are often associated with young, hot stars that emit large amounts of ultraviolet radiation, which ionizes the surrounding gas and causes it to glow. The glowing gas emits light of various colors, depending on the chemical composition of the nebula and the temperature of the gas. Some common emission nebulae include the Orion Nebula, the Lagoon Nebula, and the Trifid Nebula.