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Created page with "{{Night Sky | image = | designation =NGC 6888<br/>Sharpless 105 | rightascension =20<sup>h</sup> 12<sup>m</sup> 07<sup>s</sup><ref name=simbad>{{cite w..."
{{Night Sky
| image =
| designation =[[NGC]] 6888<br/>Sharpless 105
| rightascension =20<sup>h</sup> 12<sup>m</sup> 07<sup>s</sup><ref name=simbad>{{cite web|url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=crescent+nebula&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id|title=NGC 6888|accessdate=2019-09-01|work=Simbad Astronomical Database|publisher=simbad.u-strasbg.fr}}</ref>
| declination =+38° 21′ 18″
| distance =5,000 ly<ref name=apod>{{cite web|url=https://apod.nasa.gov/apod/ap160610.html|title=NGC 6888: The Crescent Nebula|accessdate=2019-09-01|publisher=apod.nasa.gov|date=2016-06-10}}</ref>
| constellation =Cygnus
| type =Emission nebula
| dimensions =
| magnitude =
| redshift =
| radvelocity =
| propmotion =
| parallax =
}}
The '''Crescent nebula''' ([[NGC]] 6888, Sharpless 105, Caldwell 27) is an [[emission nebula]] situated in the [[constellation]] of [[Cygnus]], the [[swan]].<ref name=apod/> The nebula consists of a central [[Wolf-Rayet star]], designated WR 136, enveloped by a bubble of [[gas]] that is 25 ly wide.<ref name=apod/> The central star is thought to have a mass of 25-40 [[solar masses]] and ejected the gas that surrounds it to form the nebula through strong [[stellar wind]]s.<ref>
{{cite journal
|last1=Esteban |first1=C.
|last2=Mesa-Delgado |first2=A.
|last3=Morisset |first3=C.
|last4=García-Rojas |first4=J.
|display-authors=3
|title=The chemical composition of Galactic ring nebulae around massive stars
|journal=Monthly Notices of the Royal Astronomical Society
|volume=460
|issue=4|page=4038-4062|date=2016
|doi=10.1093/mnras/stw1243
|bibcode=2016MNRAS.460.4038E
|ref=harv
}} {{arXiv|1605.07800}}</ref><ref name=space>{{cite web|url=https://www.space.com/14598-crescent-nebula-skywatching-photo.html|title=Booming Crescent Nebula Shines in Skywatcher Photo|accessdate=2019-09-01|publisher=space.com|author=Nina Sen|date=2012-02-28}}</ref> Since the original material was ejected, faster moving material has been ejected that has slammed into the previously ejected material. Where this material collides, the gas is heated up, so much that it emits [[x-ray]]s.<ref name=esa>{{cite web|url=https://www.esa.int/spaceinimages/Images/2017/12/Crescent_nebula|title=Crescent Nebula|accessdate=2019-09-01|publisher=esa.int|date=2017-12-11}}</ref>
The nebula is located around 5,000 light years away.<ref name=esa/> Measurements of the x-ray emission of the nebula using the EPIC camera on the XMM-Newton satellite. The x-ray emitting gas is so hot it has turned into a [[plasma]]. It has been found to be well described by a model using two [[temperature]]s of 1.4×10<sup>6</sup> k and 8.2×10<sup>8</sup> k.<ref name=xray>
{{cite journal
|last1=Toalá |first1=J.
|last2=Guerrero |first2=M.
|last3=Chu |first3=Y.
|last4=Arthur |first4=S.
|last5=Tafoya |first5=D.
|last6=Gruendl |first6=R.
|display-authors=3
|title=X-ray emission from the Wolf–Rayet bubble NGC 6888 – II.XMM–NewtonEPIC observations
|journal=Monthly Notices of the Royal Astronomical Society
|volume=456
|issue=4|page=4305-4314|date=2016
|doi=10.1093/mnras/stv2819
|bibcode=2016MNRAS.456.4305T
|ref=harv
}} {{arXiv|1310.2801}}</ref> The [[electron]] [[density]] has been found to be around 0.4 cm<sup>-3</sup> for this plasma.<ref name=xray/> Inhomogeneities in the [[nitrogen]] abundance and temperature distribution have also been detected.
==References==
{{Reflist}}
{{Nebulae}}
[[Category:Astronomy]]
[[Category:Nebulae]]
| image =
| designation =[[NGC]] 6888<br/>Sharpless 105
| rightascension =20<sup>h</sup> 12<sup>m</sup> 07<sup>s</sup><ref name=simbad>{{cite web|url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=crescent+nebula&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id|title=NGC 6888|accessdate=2019-09-01|work=Simbad Astronomical Database|publisher=simbad.u-strasbg.fr}}</ref>
| declination =+38° 21′ 18″
| distance =5,000 ly<ref name=apod>{{cite web|url=https://apod.nasa.gov/apod/ap160610.html|title=NGC 6888: The Crescent Nebula|accessdate=2019-09-01|publisher=apod.nasa.gov|date=2016-06-10}}</ref>
| constellation =Cygnus
| type =Emission nebula
| dimensions =
| magnitude =
| redshift =
| radvelocity =
| propmotion =
| parallax =
}}
The '''Crescent nebula''' ([[NGC]] 6888, Sharpless 105, Caldwell 27) is an [[emission nebula]] situated in the [[constellation]] of [[Cygnus]], the [[swan]].<ref name=apod/> The nebula consists of a central [[Wolf-Rayet star]], designated WR 136, enveloped by a bubble of [[gas]] that is 25 ly wide.<ref name=apod/> The central star is thought to have a mass of 25-40 [[solar masses]] and ejected the gas that surrounds it to form the nebula through strong [[stellar wind]]s.<ref>
{{cite journal
|last1=Esteban |first1=C.
|last2=Mesa-Delgado |first2=A.
|last3=Morisset |first3=C.
|last4=García-Rojas |first4=J.
|display-authors=3
|title=The chemical composition of Galactic ring nebulae around massive stars
|journal=Monthly Notices of the Royal Astronomical Society
|volume=460
|issue=4|page=4038-4062|date=2016
|doi=10.1093/mnras/stw1243
|bibcode=2016MNRAS.460.4038E
|ref=harv
}} {{arXiv|1605.07800}}</ref><ref name=space>{{cite web|url=https://www.space.com/14598-crescent-nebula-skywatching-photo.html|title=Booming Crescent Nebula Shines in Skywatcher Photo|accessdate=2019-09-01|publisher=space.com|author=Nina Sen|date=2012-02-28}}</ref> Since the original material was ejected, faster moving material has been ejected that has slammed into the previously ejected material. Where this material collides, the gas is heated up, so much that it emits [[x-ray]]s.<ref name=esa>{{cite web|url=https://www.esa.int/spaceinimages/Images/2017/12/Crescent_nebula|title=Crescent Nebula|accessdate=2019-09-01|publisher=esa.int|date=2017-12-11}}</ref>
The nebula is located around 5,000 light years away.<ref name=esa/> Measurements of the x-ray emission of the nebula using the EPIC camera on the XMM-Newton satellite. The x-ray emitting gas is so hot it has turned into a [[plasma]]. It has been found to be well described by a model using two [[temperature]]s of 1.4×10<sup>6</sup> k and 8.2×10<sup>8</sup> k.<ref name=xray>
{{cite journal
|last1=Toalá |first1=J.
|last2=Guerrero |first2=M.
|last3=Chu |first3=Y.
|last4=Arthur |first4=S.
|last5=Tafoya |first5=D.
|last6=Gruendl |first6=R.
|display-authors=3
|title=X-ray emission from the Wolf–Rayet bubble NGC 6888 – II.XMM–NewtonEPIC observations
|journal=Monthly Notices of the Royal Astronomical Society
|volume=456
|issue=4|page=4305-4314|date=2016
|doi=10.1093/mnras/stv2819
|bibcode=2016MNRAS.456.4305T
|ref=harv
}} {{arXiv|1310.2801}}</ref> The [[electron]] [[density]] has been found to be around 0.4 cm<sup>-3</sup> for this plasma.<ref name=xray/> Inhomogeneities in the [[nitrogen]] abundance and temperature distribution have also been detected.
==References==
{{Reflist}}
{{Nebulae}}
[[Category:Astronomy]]
[[Category:Nebulae]]