An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star. Among the several different types of emission nebulae are H II regions, in which star formation is taking place and young, massive stars are the source of the ionizing photons; and planetary nebulae, in which a dying star has thrown off its outer layers, with the exposed hot core then ionizing them.

General information

Usually, a young star will ionize part of the same cloud from which it was born, although only massive, hot stars can release sufficient energy to ionize a significant part of a cloud. In many emission nebulae, an entire cluster of young stars is doing the work.

The nebula's color depends on its chemical composition and degree of ionization. Due to the prevalence of hydrogen in interstellar gas, and its relatively low energy of ionization, many emission nebulae appear red due to the strong emissions of the Balmer series. If more energy is available, other elements will be ionized and green and blue nebulae become possible. By examining the spectra of nebulae, astronomers infer their chemical content. Most emission nebulae are about 90% hydrogen, with the remaining helium, oxygen, nitrogen, and other elements.

Some of the most prominent emission nebulae visible from the northern hemisphere are the North America Nebula (NGC 7000) and Veil Nebula NGC 6960/6992 in Cygnus, while in the south celestial hemisphere, the Lagoon Nebula M8 / NGC 6523 in Sagittarius and the Orion Nebula M42.[1] Further in the southern hemisphere is the bright Carina Nebula NGC 3372.

Emission nebulae often have dark areas in them which result from clouds of dust which block the light.

Many nebulae are made up of both reflection and emission components such as the Trifid Nebula.
Image gallery

Emission nebula LHA 120-N 55 in the Large Magellanic Cloud.[2]

Hubble image of emission nebula NGC 2174.[3]

See also

Herbig–Haro object

Wikimedia Commons has media related to Emission nebulae.

McArthur, Frommert; Kronberg, Christine (12 April 2006). "Messier 42". Messier Object Index. Retrieved 17 July 2007.
"A Beautiful Instance of Stellar Ornamentation". Retrieved 19 May 2016.

"Hubble revisits the Monkey Head Nebula for 24th birthday snap". ESA/Hubble Press Release. Retrieved 10 April 2014.


Visible nebula

Dark nebula Diffuse nebula
Emission nebula
Planetary nebula Supernova remnant Nova remnant H II region Reflection nebula
Variable nebula Preplanetary nebula

Pre-stellar nebula

Giant molecular cloud Bok globule Evaporating gaseous globule Solar nebula

Stellar nebula

Nova remnant Protoplanetary nebula Wolf–Rayet nebula

Post-stellar nebula

Planetary nebula Supernova remnant Pulsar wind nebula Supershell


Interstellar cloud
Molecular cloud Infrared cirrus High-velocity cloud H I region


Bipolar nebula Pinwheel nebula

List-Class article Lists

Diffuse Planetary (PNe) Protoplanetary (PPNe) Supernova remnants (SNRs)

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