Editing Saturn Nebula

{{short description|Planetary nebula in the constellation Aquarius}}
{{Planetary nebula |
| image = [[Image:MUSE image of the Saturn Nebula.jpg|300px]]
| caption = NGC 7009 by [[Very Large Telescope]].<ref>{{cite web|title=The Strange Structures of the Saturn Nebula|url=http://www.eso.org/public/news/eso1731/|website=www.eso.org|access-date=27 September 2017}}</ref>
| name = Saturn Nebula
| type = Planetary
| epoch = J2000.0
| ra = {{RA|21|04|10.877}}<ref name="simbad">{{cite simbad
  | title=NAME Saturn Nebula
  | access-date=2006-12-26}}</ref>
| dec = {{DEC|-11|21|48.25}}<ref name="simbad" />
| dist_ly = [[1 E19 m|2000-4000]] [[light year|ly]]<br />''(See article)''
| appmag_v = 8.0<ref name="messierseds">{{cite web
  | title=Messier Online Astronomical Database
  | work=Saturn Nebula
  | url=http://messier.seds.org/xtra/ngc/n7009.html
  | access-date=2012-08-28}}</ref>
| size_v = 41″ × 35″<ref name="simbad" />
| constellation = [[Aquarius (constellation)|Aquarius]]
| radius_ly = 0.2 to 0.4
| absmag_v = 2.5 to 1
| notes = -
| names = NGC 7009,<ref name="simbad" /> [[Caldwell catalogue|Caldwell]] 55
}}

The '''Saturn Nebula''' (also known as '''NGC 7009''' or '''Caldwell 55''') is a [[planetary nebula]] in the [[constellation]] [[Aquarius (constellation)|Aquarius]]. It appears as a greenish-yellowish hue in a small [[amateur telescope]]. It was discovered by [[William Herschel]] on September 7, 1782, using a telescope of his own design in the garden at his home in [[Datchet]], [[England]], and was one of his earliest discoveries in his sky survey. The nebula was originally a [[low-mass star]] that ejected its layers into space, forming the nebula. The central star is now a bright [[white dwarf|white dwarf star]] of [[apparent magnitude]] 11.5. The Saturn Nebula gets its name from its superficial resemblance to the [[planet Saturn]] with its rings nearly edge-on to the observer. It was so named by [[Lord Rosse]] in the 1840s, when telescopes had improved to the point that its Saturn-like shape could be discerned.  [[William Henry Smyth]] said that the Saturn Nebula was one of [[Otto Wilhelm von Struve|Struve's]] nine "Rare Celestial Objects".<ref>{{Cite web|title=NGC 7009, the Saturn Nebula|url=https://www.messier.seds.org/xtra/ngc/n7009.html|access-date=2020-12-26|website=www.messier.seds.org}}</ref>

The Saturn Nebula is a complex planetary nebula and contains many morphological and kinematic sub-systems in three dimensions.  It includes a halo, jet-like streams, multiple shells, ansae ("handles"), and small-scale filaments and knots.  The ansae are expanding non-radially from the central star.<ref name="Steffenetal2009">{{cite journal
 | title = The 3D velocity structure of the planetary nebula NGC 7009

 | date = October 2009
 | journal = Revista Mexicana de Astronomía y Astrofísica
 | bibcode = 2009RMxAA..45..143S
 | volume = 45
 | pages = 143–54
 | quote = NGC 7009 is a planetary nebula with several morphological and kinematical sub-systems with multiple shells, a halo, jet-like streams, ansae and small-scale filaments and knots.
 | author = Steffen, W.
 | author2 = Espíndola, M.
 | author3 = Martínez, S.
 | author4 = Koning, N.

|arxiv = 0905.2148 }}</ref> Although the ansae are most prominent in the Saturn Nebula, they are also visible in other planetary nebulae, including [[NGC 3242]], [[Cat's Eye Nebula|NGC 6543]] and [[NGC 2371-2]].

The distance of the Saturn Nebula is not known precisely. {{harvnb|Sabbadin|Turatto|Cappellaro|Benetti|2004}} estimates the distance to be 5,200 [[light-years]] (1.6 [[parsec|kpc]]).  In 1963 O'Dell estimated it to be 3,900 light-years (1.2 kpc), which gives an approximate diameter of 0.5 light years for the object as a whole.

The central star, a very hot bluish dwarf with a temperature of 55,000 K, from which the nebula is believed to originate, has an absolute magnitude of +1.5, which equates to a luminosity of about 20 [[Solar luminosity|solar luminosities]] and a visual magnitude of 11.5. This strong ultraviolet irradiation from the central star creates the characteristic fluorescent green tint of the nebula via the radiation of doubly ionized oxygen. The object overall has a visual magnitude of 8 and a radial velocity of 28 miles per second towards the [[Earth]].

The nebula is 1 degree west of the star [[Nu Aquarii]]. The central portion measures 25″ × 17″, while the outer shell extends to 41″ × 35″.  The object is on many "best of" observing lists.<ref>[http://messier.seds.org/xtra/similar/sac110bn.html SAC 110 best NGC object list]</ref><ref>[http://messier.seds.org/xtra/similar/rasc-dsc.html RASC's Finest N.G.C. Objects O[http://messier.seds.org/xtra/similar/caldwell.html The Caldwell Catalog]&nbsp;(#55)</ref>

==Imaging==
<gallery>
NGC 7009 Lord Rosse.jpg|1848 drawing of NGC 7009 by [[Lord Rosse]].
Looking at the Saturn Nebula in 3D.webm| This visualisation shows three-dimensional MUSE data of the nebula.
</gallery>

==Notes==
{{reflist}}

==References==
* {{Cite journal

 | date = March 2004
 | title = The 3-D ionization structure and evolution of NGC 7009 (Saturn Nebula)
 | last1 = Sabbadin
 | first1 = Franco
 | last2 = Turatto
 | first2 = M.
 | last3 = Cappellaro
 | first3 = E.
 | last4 = Benetti
 | first4 = S.
 | last5 = Ragazzoni
 | first5 = R.
 | journal = Astronomy and Astrophysics
 | volume = 416
 | issue = 3
 | pages = 955–81
 | doi = 10.1051/0004-6361:20031729
 | bibcode = 2004A&A...416..955S
 |arxiv = astro-ph/0312261 | s2cid = 16243759
 }}

==External links==
{{commonscat}}
* [http://antwrp.gsfc.nasa.gov/apod/ap971230.html NASA APOD (1997-12-30)] – NGC 7009: The Saturn Nebula
* {{WikiSky|name=The Saturn Nebula}}

{{Sky|21|04|10.877|-|11|21|48.25|3000}}

{{Catalogs|NGC=7009|C=55}}
{{Caldwell catalogue}}
{{NGC75}}
{{Aquarius (constellation)}}

{{DEFAULTSORT:Saturn Nebula}}
[[Category:Planetary nebulae]]
[[Category:Aquarius (constellation)]]
[[Category:NGC objects]]
[[Category:Caldwell objects|055b]]
[[Category:Astronomical objects discovered in 1782]]