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'''Oberon''' is the farthest moon outside of [[Uranus]] with a 760 Km ratio. It is the second largest moon in orbit of the planet.
{{Planet
|image=Oberon.jpg
|caption=Oberon, taken by Voyager 2
|date=January 11, 1787<ref name=usgs>"[http://planetarynames.wr.usgs.gov/append7.html Gazetteer of Planetary Nomenclature: Planetary Body Names and Discoverers]." US Geological Survey, Jennifer Blue, ed. March 31, 2008. Accessed April 17, 2008.</ref>
|discname=William Herschel<ref name=usgs/><ref name=Hamilton>Hamilton, Calvin J. "[http://www.solarviews.com/eng/oberon.htm Entry for Oberon]." ''Views of the Solar System'', 2001. Accessed June 16, 2008.</ref>
|origname=King of the fairies in the play ''A Midsummer Night's Dream'' by William Shakespeare<ref name=Hamilton/><ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/oberon.html Entry for Oberon]." ''The <s>Nine</s> 8 Planets'', December 22, 2004. Accessed June 16, 2008.</ref>
|primary=Uranus
|order=18
|periapsis=583,053 km<ref name=calc>Calculated</ref>
|apoapsis=583,987 km<ref name=calc/>
|semimajor=583,520 km<ref name=uranussatfact>Williams, David R. "[http://nssdc.gsfc.nasa.gov/planetary/factsheet/uraniansatfact.html Uranian Satellite Fact Sheet]." National Space Science Data Center, [[National Aeronautics and Space Administration|NASA]], November 23, 2007. Accessed June 16, 2008.</ref>
|eccentricity=0.0008<ref name=uranussatfact/>
|sidereal=13.463239 da<ref name=uranussatfact/>
|orbitspeed=3.15 km/s<ref name=Hamilton/>
|inclination=0.10°<ref name=uranussatfact/>
|siderealday=13.463239 da<ref name=uranussatfact/>
|rotatespeed=0.00411 km/s<ref name=calc/>
|axialtilt=0°<ref name=uranussatfact/>
|mass=3.01 * 10<sup>21</sup> kg<ref name=uranussatfact/>
|density=1630 kg/m³<ref name=uranussatfact/>
|meanradius=761.4 km<ref name=uranussatfact/>
|surfacegrav=0.3469 m/s²<ref name=calc/>
|escapespeed=0.7268 km/s<ref name=calc/>
|surfacearea=7,285,102 km²<ref name=calc/>
|meantemp=61 K
|composition=Water ice and rock<ref name=Arnett/>
|color=#CC9966
|albedo=0.25<ref name=uranussatfact/>
}}'''Oberon''' or '''Saturn IV''' is the eighteenth [[moon]] of [[Uranus]], and the outermost of the major moons of Uranus. It is also the second largest moon of Uranus.<ref name=Arnett/><ref name=Britannica>Ingersoll, Andrew P. "[http://www.britannica.com/eb/article-9056637 Oberon]." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 16 June 2008.</ref>
== Name ==
== Discovery and naming ==
Oberon, like the other moons of the same planet, have names from various productions of [[Shakespeare]].
[[William Herschel]] discovered Oberon and its inner companion, [[Titania]], on January 11, 1787.<ref name=usgs/>
Sir [[John Herschel]], his son, gave to Oberon the name of the king of the fairies in [[William Shakespeare]]'s comedy, ''[[A Midsummer Night's Dream]]''.<ref name=usgs/><ref name=Lassell3>Lassell, William. "[http://articles.adsabs.harvard.edu//full/1852AN.....34..325./0000169.000.html Beobachtungen der Uranus-Satelliten]." ''Astronomische Nachrichten'' 34:325-328, 1852. Accessed June 16, 2008.</ref>
== Discovery ==
== Orbital characteristics ==
Oberon is in a slightly eccentric orbit around Uranus, at an average distance of 583,520 km. Its sidereal month is about 13.46 [[Earth]] days.<ref name=uranussatfact/><ref name=Britannica/>
The moon was discovered by [[William Herschel]] along with five others that he found within a few years of each other.
== Rotational characteristics ==
Oberon is in [[tidal lock]] with Uranus.<ref name=uranussatfact/><ref name=Britannica/>
== Physical characteristics ==
Oberon is the second largest of the moons of Uranus. It is probably composed of [[water]] ice and rock.<ref name=Arnett/><ref name=Britannica/>
=== Surface ===
The surface of Oberon has many impact craters. Many of these have bright rays that radiate from them, similar to those found on [[Callisto]].<ref name=Hamilton/><ref name=Arnett/><ref name=Britannica/>
The surface, including many of the crater floors, is partially covered with a dark material of unknown origin. Some astronomers speculate that this material is an aqueous solution that upwelled from the interior.<ref name=Hamilton/><ref name=Britannica/>
== Problems for uniformitarian theories posed by Oberon ==
Oberon poses the same problem for [[uniformitarianism|uniformitarian]] astronomy as do all the other moons of Uranus: its orbit is inclined severely to the ecliptic, though not to Uranus' own equator. How the Uranian system came to have such an inclination has never been explained.
== Observation and Exploration ==
Oberon is visible on a dark sky through a telescope having an aperture of 30 cm or more.<ref name=Arnett/>
The only spacecraft to explore Oberon has been [[Voyager 2]]. It approached to within 470,600 km of Oberon on January 24, 1986, and took a small number of images.<ref name=Voyager1>"[http://pds-rings.seti.org/voyager/mission/#v2uenc Voyager Mission Description: Voyager 2 Uranus Encounter]." February 19, 1997. Accessed June 13, 2008.</ref><ref name=Smith>Smith, B.A., Soderblom, L.A., Beebe, R., ''et al.'' "[http://adsabs.harvard.edu/abs/1986Sci...233...43S Voyager 2 in the Uranian system - Imaging science results]." ''Science'' 233:43-64, July 4, 1986. Accessed June 13, 2008.</ref> No other detailed images are available.
== References ==
{{reflist|2}}
{{Solarsystem}}