The six largest moons of Uranus, from left to right: Puck, Miranda, Ariel, Umbriel, Titania and Oberon

The planet Uranus was discovered by William Herschel in 1781. It's named for Saturn's father, the ancient Greek sky god Ouranos. It has at least 27 moons, most of them not discovered until the 20th century.

After Uranus was discovered, it took 167 years to find its five large moons.

• Herschel discovered Titania and Oberon in 1787.
• English astronomer William Lassell discovered Ariel and Umbriel in 1851.
• Dutch-American astronomer Gerard Kuiper discovered Miranda in 1948.
• All the others were discovered after 1985, most of them by NASA's Voyager 2 mission.

William Lassell asked Herschel's son, Sir John Herschel, to suggest names for the moons. Instead of the usual names from mythology, Herschel turned to literature.
Oberon and Titania are the king and queen of the fairies in Shakespeare's A Midsummer Night's Dream, and Ariel and Umbriel were spirits of the air in a popular poem of the time.

Gerard Kuiper followed the Shakespearian theme by naming his discovery Miranda after a character in The Tempest.

In order of size, the five main moons are Titania, Oberon, Umbriel, Ariel and Miranda.
The sizes of the moons vary from Titania's 1500 km across (930 miles) to Miranda's 470 km (290 miles). The whole moon system is less massive than that of the other giant planets. The total mass of Uranus's five largest moons is less than half that of Neptune's moon Triton.

The large moons are dark and heavily cratered.
Except for Miranda, they're about half and half rock and ice. And except for Umbriel, they show signs of geological activity that has made deep canyons and cracks, and covered over craters. Umbriel has the oldest surface, and Ariel has the youngest surface with the fewest craters.

Miranda is the odd one out – it's one of the weirdest bodies in the Solar System.
Miranda is made mostly of ice, and has a rugged surface criss-crossed by huge canyons. This shows that there has been intense geological activity in the past. And since some of the surface has fewer craters than we'd expect, Miranda could still be active. Someone described Miranda as looking like "a giant smashed it apart and then put it back together blindfolded."

We know that Uranus also has at least 13 small inner moons.
These tiny moons formed along with the planet. They're all dark and lumpy, and orbit Uranus in less than a day. They move in circular orbits in the same direction as the planet does.

As well as moons, Uranus also has at least 13 rings and some of the inner moons are shepherd moons.
In 1977, several narrow, dark rings were discovered. No one had seen rings around Uranus since William Herschel reported one in 1797. There are two known shepherd moons and their gravity keeps a ring in place. There is also some evidence of other shepherd moons.

Nine irregular outer moons have been discovered – they are captured objects.
All of these moons have been discovered since 1997, and they're little and lumpy like the inner moons. Their sizes vary from Trinculo's 20 km across (12 miles) to Sycorax's 120 km (75 miles).

The outer moons are a long way away from the planet in eccentric orbits.
A circle is itself not eccentric, but the more squashed a circle gets, the more eccentric it is. Margaret has one of the most eccentric orbits of any known moon. The farthest large moon from Uranus is Oberon. But the closest outer moon is seven times farther away than that and the most distant one over 35 times farther away.