Uranus, the seventh planet of the
Solar System, has 27 known
moons, all of which are named after characters from the works of
William Shakespeare and
Alexander Pope. Uranus's moons are divided into three groups: thirteen inner moons, five major moons, and nine irregular moons. The inner moons are small dark bodies that share common properties and origins with the
Uranus's rings. The five major moons are massive enough to have reached
hydrostatic equilibrium, and four of them show signs of internally driven processes such as canyon formation and volcanism on their surfaces. The largest of these five, Titania, is 1,578 km in diameter and the
eighth-largest moon in the Solar System, and about one-twentieth the mass of the
Moon. The orbits of the regular moons are nearly
coplanar with Uranus's equator, which is tilted 97.77° to its orbit. Uranus's irregular moons have elliptical and strongly inclined (mostly
retrograde) orbits at large distances from the planet.