The first two of Uranus's five large moons, Titania and Oberon, were found by William Herschel in 1787. The third and fourth moons, Ariel and Umbriel, were not discovered until 1851. Miranda, the fifth, held out until 1948. These major moons certainly pose a challenge to observers: the brightest is Titania, at magnitude 13.7, and the dimmest, Miranda, is 16th magnitude.
Due to their faintness, little was known of these moons until Voyager 2's visit. Its cameras revealed Oberon and Umbriel to be heavily cratered worlds of ice and rock, with no sign of geological activity. Ariel and Titania, on the other hand, appear to have undergone some kind of icy volcanism that has "relaxed" their surfaces, erasing craters in many areas and producing long fault valleys.
The surprise was Miranda. It displays a geology so complex that, more than a decade after the Voyager visit, scientists are still arguing about what causes its dominant feature—the grooved terrain known as coronae. One theory is that Miranda is a second-generation satellite, reassembled out of a shattered moon or moons. Its surface shows three enormous coronae, whose roughly oval patterns may mark places where large fragments sank into Miranda's interior.
Voyager 2 also showed that Uranus has 10 more moons, all of them small, dark mixtures of ice and rock. Like the larger moons, these have been named after Shakespearean characters, including Ophelia, Portia, Juliet, Desdemona, and Puck.