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Oberon, taken by Voyager 2
Date of discovery Date of discovery::January 11, 1787[1]
Name of discoverer Discoverer::William Herschel[1][2]
Name origin Name origin::King of the fairies in the play ''A Midsummer Night's Dream'' by William Shakespeare[2][3]
Orbital characteristics
Celestial class Member of::Moon
Primary Primary::Uranus
Order from primary Order::18
Periuranion Periapsis::583,053 km[4]
Apuranion Apoapsis::583,987 km[4]
Semi-major axis Semi-major axis::583,520 km[5]
Orbital eccentricity Orbital eccentricity::0.0008[5]
Sidereal month Sidereal period::13.463239 da[5]
Avg. orbital speed Orbital speed::3.15 km/s[2]
Inclination Inclination::0.10° to Uranus's equator[5]
Rotational characteristics
Sidereal day Sidereal day::13.463239 da[5]
Rotation speed Rotation speed::0.00411 km/s[4]
Axial tilt Axial tilt::0°[5]
Physical characteristics
Mass 3.01 * 1021 kg[5]
Mean density Planet density::1630 kg/m³[5]
Mean radius Mean radius::761.4 km[5]
Surface gravity Surface gravity::0.3469 m/s²[4]
Escape speed Escape speed::0.7268 km/s[4]
Surface area Lunar surface area::7,285,102 km²[4]
Mean temperature Mean temperature::61 K
Composition Composition::Water ice and rock[3]
Color Color::#CC9966
Albedo Albedo::0.25[5]

Oberon or Uranus 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.[3][6]

Discovery and naming

William Herschel discovered Oberon and its inner companion, Titania, on January 11, 1787.[1]

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.[1][7]

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.[5][6]

Rotational characteristics

Oberon is in tidal lock with Uranus.[5][6]

Physical characteristics

Oberon is the second largest of the moons of Uranus. It is probably composed of water ice and rock.[3][6]


The surface of Oberon has many impact craters. Many of these have bright rays that radiate from them, similar to those found on Callisto.[2][3][6]

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.[2][6]

Problems for uniformitarian theories posed by Oberon

Oberon poses the same problem for 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.[3]

The only spacecraft to explore Oberon has been Visiting mission::Voyager 2. It approached to within 470,600 km of Oberon on January 24, 1986, and took a small number of images.[8][9] No other detailed images are available.


  1. 1.0 1.1 1.2 1.3 "Gazetteer of Planetary Nomenclature: Planetary Body Names and Discoverers." US Geological Survey, Jennifer Blue, ed. March 31, 2008. Accessed April 17, 2008.
  2. 2.0 2.1 2.2 2.3 2.4 Hamilton, Calvin J. "Entry for Oberon." Views of the Solar System, 2001. Accessed June 16, 2008.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 Arnett, Bill. "Entry for Oberon." The Nine 8 Planets, December 22, 2004. Accessed June 16, 2008.
  4. 4.0 4.1 4.2 4.3 4.4 4.5 Calculated
  5. 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 Williams, David R. "Uranian Satellite Fact Sheet." National Space Science Data Center, NASA, November 23, 2007. Accessed June 16, 2008.
  6. 6.0 6.1 6.2 6.3 6.4 6.5 Ingersoll, Andrew P. "Oberon." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 16 June 2008.
  7. Lassell, William. "Beobachtungen der Uranus-Satelliten." Astronomische Nachrichten 34:325-328, 1852. Accessed June 16, 2008.
  8. "Voyager Mission Description: Voyager 2 Uranus Encounter." February 19, 1997. Accessed June 13, 2008.
  9. Smith, B.A., Soderblom, L.A., Beebe, R., et al. "Voyager 2 in the Uranian system - Imaging science results." Science 233:43-64, July 4, 1986. Accessed June 13, 2008.
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