Oberon (moon) numbering (where Titania and Oberon are II and IV). In 1851 Lassell eventually numbered all four known satellites in order of their distance from the planet by Roman numerals, and since then Oberon has been designated '. Oberon orbits Uranus at a distance of about 584,000 km, being the farthest from the planet among its five major moons. Oberon's orbit has a small orbital eccentricity and inclination relative to the equator of Uranus. Its orbital period is around 13.5 days, coincident with its rotational period. In other words, Oberon is a synchronous satellite, tidally locked, with one face always pointing
Fictional planets of the Solar System while yet others are purely fictional and were never intended as serious hypotheses about the structure of the Solar System. Vulcan was a hypothetical planet supposed to revolve around the Sun inside the orbit of Mercury, invoked to explain certain irregularities in Mercury's orbit. The planet was proposed as a hypothesis in 1859, and abandoned not later than 1915. The name "Vulcan" has been used for various other fictional planets, in and out of the Solar System, that do not correspond to the hypothetical planet Vulcan. The planet Vulcan in the "Star Trek" franchise, for instance, is specified as orbiting