Oberon, imaged by Voyager 2 on Jan. 24, 1986, from a distance of 660,000 km.

Oberon is the second largest moon of Uranus and the 18th in order from the planet. Oberon was discovered by William Herschel on January 11, 1787. It is named after the king of the Fairies in Shakespeare's A Midsummer Night's Dream and is also known as Uranus IV.


Oberon's heavily cratered surface, featuring far more and larger craters than do Ariel or Titania, is clearly ancient. Some of the craters have bright rays similar to those seen on Jupiter's moon Callisto and some of the crater floors are dark – covered perhaps with a mixture of carbonaceous substances and ice that erupted from below. Large faults run across the entire southern hemisphere, indicating geologic activity in Oberon's youth. In the image shown here, note the large mountain, about 6 km high, that stands out on the lower left limb.


discovery 1787, by William Herschel
semimajor axis 582,600 km (361,860 miles)
diameter 1,523 km (947 miles)
mean density 1.64 g/cm3
escape velocity 0.729 km/s (2,624 km/h,
1,631 mph)
orbital period 13.463 days (13 d 11 hr)
orbital eccentricity 0.0008
orbital inclination 0.10º
axial period 13.463 days
visual albedo 0.24