The outermost of the five major moons of Uranus and the second largest is Oberon, which was discovered in 1787 by William Herschel. As with Titania, it was also named by William's son for a character in William Shakespeare's play A Midsummer Night's Dream.
(362,000 miles), and its orbital period is 13.46 days. Like all of Uranus's large moons, Oberon rotates synchronously with its orbital period, keeping the same hemisphere toward the planet and the same hemisphere forward in its orbit. The moon has a diameter of 1,522 km (946 miles) and a density of 1.63 g/cm3 (0.94 oz/in3).
Photographic images transmitted by the U.S. Voyager 2 spacecraft when it flew past the Uranian system in 1986 revealed that Oberon's surface is old and that a few of the numerous bright craters appear to have been flooded by some kind of dark material that upwelled from the moon's interior.