View source for NGC 281

{{short description|Emission nebula in the constellation Cassiopeia}}
{{Infobox nebula
| image = PacMan Nebula, NGC 281.jpg
| caption= 
| constellation = [[Cassiopeia constellation|Cassiopeia]]
| name = [[New General Catalogue|NGC]] 281
| type = H II region
| epoch = J2000.0
|ra ={{RA|00|52|59.3}}<ref name="ned">{{cite web
  |title=NASA/IPAC Extragalactic Database
  |work=Results for NGC 281
  |url=http://nedwww.ipac.caltech.edu/
  |access-date=2006-10-17}}</ref>
|dec = {{DEC|+56|37|19}}<ref name="ned" />
|dist_ly = [[1 E19 m|9500]]<ref name="Leassetal2001">{{cite journal
  |author=Leass, E. A.
  |author2=Biller, B.
  |author3=Dame, T. M.
  |author4=Megeath, S. T.
  |title=An Expanding Complex of Molecular Clouds High Above the Perseus Spiral Arm
  |journal=American Astronomical Society, 199th AAS Meeting, #91.16; Bulletin of the American Astronomical Society
   |date=2001
   |volume=33
   |pages=1439
   |bibcode=2001AAS...199.9116L }}</ref>
|dist_pc=2900
|appmag_v=
|size_v=35{{prime}}
|radius_ly=48 
|absmag_v=  
|notes=[[open cluster]] [[IC 1590]], the multiple star B 1, and several [[Bok globule]]s
|names=[[Index Catalogue|IC]] 11, Sh2-184,<ref name="simbad">{{cite simbad
|title=NGC 281
|access-date=18 March 2017}}</ref> [[Sharpless catalog|Sharpless]] 184,<ref name="ned" /> [[Lynds' Catalogue of Bright Nebulae|LBN]] 616, [[Lynds' Catalogue of Bright Nebulae|LBN]] 123.17-06.28, Pacman Nebula}}

'''NGC 281''', '''IC 11''' or '''Sh2-184''' is a bright [[emission nebula]] and part of an [[H II region]] in the northern constellation of [[Cassiopeia constellation|Cassiopeia]] and is part of the [[Milky Way]]'s [[Perseus Spiral Arm]]. This 20×30 [[arc minute|arcmin]] sized nebulosity is also associated with [[open cluster]] [[IC 1590]], several [[Bok globule]]s and the multiple star, B 1. It collectively forms Sh2-184,<ref name="simbad" /> spanning over a larger area of 40 arcmin.<ref name="Sharpless1959">{{cite journal
|last=Sharpless |first=S.
|year=1959
|title=A Catalogue of H II Regions
|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1959ApJS....4..257S
|journal=[[Astrophysical Journal Supplement]]
|volume=4 
|pages=257
|bibcode=1959ApJS....4..257S
|doi=10.1086/190049
|access-date=18 March 2017
}}</ref> A recent distance from radio [[parallax]]es of water [[maser]]s at 22 [[hertz|GHz]] made during 2014 is estimated it lies {{val|2.82|0.20|u=kpc}} (9200 ly) from us.<ref name="Choi2014">{{cite journal
|last=Choi |first=Y.K.
|display-authors=et al. 
|year=2014
|title=Trigonometric Parallaxes of Star Forming Regions in the Perseus Spiral Arm
|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?db_key=AST&bibcode=2014ApJ...790...99C
|journal=[[Astrophysical Journal]]
|volume=790
|issue=2 
|pages=99
|arxiv=1407.1609
|doi=10.1088/0004-637X/790/2/99
|bibcode=2014ApJ...790...99C
|s2cid=118399182
|access-date=18 March 2017
}}</ref> Colloquially, NGC 281 is also known as the '''Pacman Nebula''' for its resemblance to the [[Pac-Man (character)|video game character]].

[[Edward Emerson Barnard]] discovered the nebula in August 1883, describing it as "a large faint nebula, very diffuse".  Multiple star 'B 1' or β 1 was later discovered by [[S. W. Burnham]], whose bright component is identified as the highly luminous O6 spectral class star, HD 5005 or HIP 4121. It consists of an 8th-magnitude primary with four companions at distances between 1.4 and 15.7 [[second of arc|arcsec]].  There has been no appreciable change in this quintuple system since the first measures were made in 1875.

The nebula region is visible in amateur telescopes from dark sky locations.
In his book ''Deep Sky Wonders'', [[Walter Scott Houston]] describes the appearance of the nebula in small telescopes:<ref name="WSH">{{cite book
|last=Houston
|first=Walter Scott
|author-link=Walter Scott Houston
|title=Deep-Sky Wonders
|publisher=Sky Publishing Corporation
|date=2005
|isbn=978-1-931559-23-2}}</ref>
:"There was a faint glow in the immediate vicinity of the multiple star, with an occasional impression of a much larger nebulosity...Its surface brightness was much less than that of M33 in Triangulum or NGC 205, the distant companion of the Andromeda galaxy."

==Features==
{{gallery|align=center
|File:NGC 281 from Chandra.jpg|NGC 281 in the [[optical astronomy|optical]] (red, yellow) and [[X ray astronomy|X rays]] (blue)
|File:IC 1590 HST.jpg|Young open star cluster IC 1590, which is found within NGC 281
}}

==References==
{{Reflist}}

== External links ==
{{commons category|NGC 281}}
*[http://apod.gsfc.nasa.gov/apod/ap050823.html NGC 281] Astronomy picture of the Day (August 23, 2005) at NASA
*{{APOD |date=25 August 2011|title=Portrait of NGC 281}}
*[https://web.archive.org/web/20070124180729/http://www.spacetelescope.org/images/html/opo0613a.html NGC 281 at ESA/Hubble]
*[http://deepspacemap.com/#?l=56.6043,166.7658,9 NGC 281 at Deep Space Map]


{{Sh2 objects}}
{{Ngc5}}
{{Cassiopeia (constellation)}}
{{Sky|00|52|53.8|+|56|37|29|9500}}

{{DEFAULTSORT:NGC 0281}}
[[Category:H II regions]]
[[Category:Cassiopeia (constellation)]]
[[Category:NGC objects|0281]]
[[Category:Sharpless objects]]
[[Category:Astronomical objects discovered in 1881|18811116]]
[[Category:Star-forming regions]]