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Oberon, discovered in 1787 by Sir William Herschel, is one of Uranus’ 27 moons. Herschel discovered Oberon and Titania, the planet’s largest moon, on the same day. It would be almost five decades after the moons were discovered that an astronomer other than Herschel observed them. Oberon, like all of Uranus’ moons, was named after characters in works by Alexander Pope and William Shakespeare. Oberon is the King of Fairies and the husband of Titania in Shakespeare’s play A Midsummer’s Night Dream. Before it was named in 1852, the moon was called “the second satellite of Uranus” or, after 1848, Uranus II. In 1951, the designation of Uranus’ moons was changed from the order discovered to the distance from the planet thus Oberon became Uranus IV.
Oberon is the fourth moon from Uranus and the planet’s second largest moon – Umbriel is the largest. At 3.03×1021 kg, Oberon is also the ninth most massive moon in the Solar System. Oberon’s diameter is about 1,523 kilometers. The satellite is 584,000 kilometers from the planet, although that distance changes during the moon’s orbit. Oberon is in a synchronous orbit with Uranus, meaning that it takes the same amount of time for the moon to orbit the planet as it does for it to complete a rotation; both last about 13.5 Earth days. Because Oberon is in a synchronous orbit, one side constantly faces the planet. Earth’s Moon is also in a synchronous orbit as are most of the major moons in our Solar System.
Scientists believe the moon is approximately half water ice and half dense material, which is probably a type of rock. Oberon has no atmosphere that scientists have been able to find nor does it appear to have a magnetic field.
Surface features on the satellite are also named after characters from Shakespeare plays. These features include the craters Falstaff, Lear, and Caesar. Oberon has more craters than any of the other moons of Uranus, leading scientists to think that it is an old satellite. The largest known crater is Hamlet, which has a diameter of approximately 206 kilometers. The satellite also has a mountain that is about 6 kilometers high. One of the most notable canyons on Oberon is Mommur Chasma, which is 537 kilometers long. The canyon, which was first discovered by the Voyager 2 probe in 1986, was named after the forest where King Oberon lived in Shakespeare’s play.
Astronomy Cast has an episode on Uranus.