Editing Orion Nebula (section)

==Structure==
[[File:Regioni_celesti_scelte_-_SpadaOrione.png|thumb|350px|A [[starchart]] of the Orion Nebula]]
[[File:Trapezium cluster optical and infrared comparison.jpg|thumb|Optical images reveal clouds of gas and dust in the Orion Nebula; an infrared image (right) reveals the new stars shining within.]]
The entirety of the Orion Nebula extends across a 1° region of the sky, and includes [[interstellar cloud|neutral clouds of gas and dust]], [[Star cluster|associations of stars]], [[H II region|ionized volumes of gas]], and [[reflection nebula]]e.

The Orion Nebula is part of a much larger nebula known as the [[Orion molecular cloud complex]], which extends throughout the constellation of [[Orion (constellation)|Orion]] and includes [[Barnard's Loop]], the [[Horsehead Nebula]], [[Messier 43|M43]], [[Messier 78|M78]], and the [[Flame Nebula]]. Stars are forming throughout the entire Cloud Complex, but most of the young stars are concentrated in dense clusters like the one illuminating the Orion Nebula.<ref name=Megeath>
{{cite journal
 |display-authors=etal |last1=Megeath |first1=S. T.
  |date= 2012
 |title= The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds. I. A Census of Dusty Young Stellar Objects and a Study of Their Mid-infrared Variability
 |journal=[[Astronomical Journal]]
 |volume= 144 |issue=6 |pages= 192
 |bibcode=2012AJ....144..192M
 |doi=10.1088/0004-6256/144/6/192
|arxiv = 1209.3826 |s2cid=119112861 }}</ref>
<ref name=Kuhn15>
{{cite journal
 |display-authors=etal |last1=Kuhn |first1=M. A.
  |date= 2015
 |title= The Spatial Structure of Young Stellar Clusters. II. Total Young Stellar Populations
 |journal=[[Astrophysical Journal]]
 |volume= 802 |issue=1 |pages= 60
 |bibcode=2015ApJ...802...60K
 |doi=10.1088/0004-637X/802/1/60
|arxiv = 1501.05300 |s2cid=119309858 }}</ref>

[[File:The Orion A molecular cloud from VISTA.jpg|thumb|left|Orion A molecular cloud from [[VISTA (telescope)|VISTA]] reveals many young stars and other objects.<ref>{{cite web|title=Hidden Secrets of Orion's Clouds – VISTA survey gives most detailed view of Orion A molecular cloud in the near-infrared|url=https://www.eso.org/public/news/eso1701/|website=www.eso.org|access-date=January 5, 2017}}</ref>]]

The current astronomical model for the nebula consists of an ionized ([[H II region|H II]]) region, roughly centered on [[Theta1 Orionis C|Theta<sup>1</sup> Orionis C]], which lies on the side of an elongated molecular cloud in a cavity formed by the massive young stars.<ref name='ODell'>
{{cite journal
 |last1=O'Dell |first1=C. R.
 |date=2001
 |title=Structure of the Orion Nebula
 |journal=[[Publications of the Astronomical Society of the Pacific]]
 |volume=113 |issue= 779|pages=29–40
 |bibcode=2001PASP..113...29O
 |doi=10.1086/317982
|doi-access=free
 }}</ref> 
(Theta<sup>1</sup> Orionis C emits 3-4 times as much photoionizing light as the next brightest star, Theta<sup>2</sup> Orionis A.) The H II region has a temperature ranging up to 10,000 K, but this temperature falls dramatically near the edge of the nebula.<ref name=Balick/> The nebulous emission comes primarily from photoionized gas on the back surface of the cavity.<ref name='ODell09'>
{{cite journal
 |last1=O'Dell |first1=C. R.
 |display-authors=etal
 |date=2009
 |title=The Three-Dimensional Dynamic Structure of the Inner Orion Nebula
 |journal=[[Astronomical Journal]]
 |volume=137 |issue=779|pages=367–382
 |bibcode= 2001PASP..113...29O|doi=10.1086/317982
|arxiv = 0810.4375 |s2cid=124923444
 }}</ref> 
The H II region is surrounded by an irregular, concave bay of more neutral, high-density cloud, with clumps of neutral gas lying outside the bay area. This in turn lies on the perimeter of the Orion molecular cloud. The gas in the molecular cloud displays a range of velocities and turbulence, particularly around the core region. Relative movements are up to {{Convert|10|km/s|mph|abbr=on}}, with local variations of up to 50&nbsp;km/s and possibly more.<ref name=Balick>
{{cite journal
 |display-authors=1|last1=Balick |first1=B.
 |last2=Gammon |first2=R. H.
 |last3=Hjellming |first3=R. M.
 |date= 1974
 |title=The structure of the Orion nebula
 |journal=[[Publications of the Astronomical Society of the Pacific]]
 |volume=86 |issue= 513|pages=616
 |bibcode=1974PASP...86..616B
 |doi=10.1086/129654
|doi-access=free
 }}</ref>

Observers have given names to various features in the Orion Nebula. The dark bay that extends from the north into the bright region is known as "Sinus Magnus",<ref>{{Cite book |first=Ronald|last=Stoyan|title=Atlas of the Messier Objects: Highlights of the Deep Sky |page=179 |publisher=Cambridge University Press |year=2008 |isbn=978-0521895545 }}</ref> also called the "Fish's Mouth". The illuminated regions to both sides are called the "Wings". Other features include "The Sword", "The Thrust", and "The Sail".<ref>"[http://messier.seds.org/m/m042.html M-42]", Students for the Exploration and Development of Space, April 12, 2006.</ref>