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Nebula
*** Shopping-Tip: Nebula
{{dablink|This article is about the interstellar cloud. For the DigiTV DVB-t card manufacturer, see
Nebula Electronics. For the science-fiction award, see
Nebula Award.}}
Image:Triangulum.nebula.full.jpg thumb|The [[NGC 604|Triangulum Emission Nebula NGC 604 lies in a spiral arm of
Galaxy M33, 2.7 million light-years from Earth. This nebula is a region in which stars are forming.]]
Image:MyCn18.JPG thumb|The MyCn18 is a young [[planetary nebula located about 8,000
light years away. This artificially colorized image was taken with the
Wide Field and Planetary Camera 2 aboard
NASA's
Hubble Space Telescope.]]
A '''nebula''' (
Latin: "mist"; pl. ''nebulae'' or ''nebulæ'', with
Æ ligature) is an
interstellar cloud of dust, gas and
Plasma (physics) plasma. Originally ''nebula'' was a general name for any extended
astronomy astronomical astronomical object object, including
galaxy galaxies beyond the
Milky Way (some examples of the older usage survive; for example, the
Andromeda Galaxy is sometimes referred to as the ''Andromeda Nebula'').
Classification of nebulae
Nebulae can be classified by how they are illuminated:
*
Diffuse nebulae are illuminated nebulae
**
Emission nebulae are internally illuminated clouds of ionized gas. Two of the most common types of emission nebula are
H II regions and
Planetary nebulae
**
Reflection nebulae are illuminated by reflections from nearby stars. An example is the nebulosity
NGC 1435 surrounding the
Pleiades (astronomy) Pleiades star cluster.
*
Planetary nebulae are compact shells of gas around a dead star or an intermittently active star. See
Nova.
*
Supernova remnants are generally moving away from their parent star at high speed, and are heated by colliding with (relatively) slow moving galactic dust and gas.
*
Dark nebulae are unilluminated. They can be detected when they obscure stars or other nebulae. Famous examples include the
Horsehead nebula in
Orion (constellation) Orion, and the
Coalsack Nebula in the
Crux Southern Cross.
Astrophysics of nebulae
H II regions are the
Stellar evolution birthplace of stars. They are formed when very diffuse
molecular clouds begin to collapse under their own gravity, often due to the influence of a nearby
supernova explosion. The cloud collapses and fragments, forming sometimes hundreds of new stars. The newly-formed stars
ionization ionize the surrounding gas to produce an emission nebula.
Other nebulae are formed by the death of stars; a star that undergoes the transition to a
white dwarf blows off its outer layer to form a
planetary nebula.
Novae and
supernovae can also create nebulae known as
nova remnants and
supernova remnants respectively.
See also
*
Solar nebula
*
Timeline of the interstellar medium and intergalactic medium
*
Messier object
*
:Category:Nebular images Images of nebulae
Category:Nebulae *
Category:Space plasmas
Category:Plasma physics
bg:МъглÑ?вина
ca:Nebulosa planetà ria
da:Stjernetåge
de:Nebel (Astronomie)
eo:Nebulozo
fr:Nébuleuse
hr:nebula
gu:નિહારિકા
io:Nebuloso
it:Nebulosa
ja:星雲
la:Nebula (Astronomia)
nl:Nevels en gaswolken
pl:Mgławica
ro:Nebuloasă
ru:ТуманноÑ?Ñ‚ÑŒ
sk:Hmlovina
sl:meglica
sv:Nebulosa
th:เนบิวลา
fi:Kaasusumu
he:ערפילית
zh:星云
*** Shopping-Tip: Nebula
