Oberon (astronomy)

Oberon (astronomy), large moon of the planet Uranus. Oberon orbits Uranus at a distance of about 583,000 km (about 350,000 mi), making it Uranus’s most distant known satellite. The moon completes one orbit in about 13.5 Earth days. Oberon’s orbit is circular and parallels Uranus’s equator. Since the planet’s equator is tilted relative to its orbit around the sun, Oberon and Uranus’s other moons have orbits nearly perpendicular to the orbits of most other worlds in the solar system.

Oberon is spherical and measures about 1520 km (about 940 mi) across, or about half the diameter of Earth’s moon. Oberon is the second largest moon of Uranus. Measurements of Oberon’s density indicate that it is about half ice and half rocky core.

Oberon has a heavily cratered surface, with many large craters indicating the moon’s great age. Cracks where the ice crust has cracked and shifted cover part of Oberon’s southern hemisphere. At the edge of photos of Oberon taken by the United States Voyager 2 probe in 1986, a lone mountain stands about 6 km (about 4 mi) high. The top layer of Oberon’s surface is dark, but asteroids that hit the moon sometimes punch through to a bright ice layer below. Apparently there is dark material below the bright icy layers because many of the craters have dark floors, as if material from inside the moon welled up to fill them. The dark material on the crater floors is the only evidence of recent geological activity on Oberon.

Oberon was discovered in 1787 by British astronomer Sir William Herschel, who named his find for a character in English playwright William Shakespeare’s play A Midsummer Night’s Dream. Herschel began the tradition of naming moons of Uranus for characters in Shakespeare’s works. Individual features on Oberon are named for places and tragic heroes in Shakespeare’s plays.