Moons of Uranus

Uranus has at least 27 moons known to orbit it. Its largest moons are Titania, Oberon, Umbriel, Ariel and Miranda. Titania and Oberon were discovered by William Herschel in 1787. Herschel was the astronomer who discovered Uranus itself six years earlier. Umbriel and Ariel were discovered by William Lassell in 1851, and Miranda was discovered by Gerard Kuiper in 1948. These five moons are all large enough to be spherical in shape.

In 1986, the spacecraft Voyager 2 reached Uranus and discovered ten small inner moons: Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda and Puck. A moon called Perdita was also imaged by Voyager 2, but it wasn't until 1999 that astronomers realised this. Since Voyager 2's visit, several even more moons have been spotted by eagle-eyed astronomers using powerful modern telescopes. These are Cupid, Mab, Francisco, Caliban, Stephano, Trinculo, Sycorax, Margaret, Prospero, Setebos and Ferdinand. Most of these are very distant outer moons.

Unlike other moons in the Solar System which are named after mythological figures, the moons of Uranus get their names from characters in works of literature written by William Shakespeare and Alexander Pope. There's even a moon called Margaret!

Not just your regular moons

Like all of the large outer planets, Uranus has a bunch of regular inner moons, a bundle of regular major moons and a collection of outer irregular moons. Regular moons are those that formed in an orbit of Uranus from materials spinning and swirling around it, irregular ones are those that Uranus has captured.

The regular inner moons orbit fairly closely to the planet and its rings, in the same direction that the planet rotates (known as prograde) and roughly on a flat plane around the planet's equator.

Major moons are the planet's largest moons. Like the inner moons, they travel in a prograde direction and orbit around Uranus' equatorial plane. Uranus orbits on its side which means that its inner moons and major moons appear to go under and over it rather than around it.

Uranus' irregular moons orbit at great distances from the planet, in orbits which can be highly eccentric (oval-shaped) and aren't on the same plane as the planet's equator. This type of orbit is called an inclined orbit. All but one of Uranus' irregular moons travel in the opposite direction (retrograde) to the rotation of the planet.

Below is a list of the moons of Uranus. They are put into colour-coded groups because it makes the page look more attractive. Oh, and because it might be useful to have them in groups too.

Groups of Uranus' Moons

Shepherd Moons (Inner Group)

Two regular moons, Cordelia and Ophelia, which orbit on either side of Uranus' narrow ε ring (ε is the Greek equivalent of letter "e"). Their orbit appears to hold the ring together and prevent it from breaking apart.

Portia Group (Inner Group)

Regular moons with shared orbital characteristics. Little is known about them other than the fact that their close orbits constantly disturb each other leading to the possibility of them colliding with each other, breaking up or crashing into Uranus at some point in their futures.

Other Inner Group Moons

A couple of other regular moons which keep themselves out of the way of the Portia moons but share a lot of other similarities.

Major Moons

Uranus' largest moons, all spherical in shape and thought to have formed from a disk of materials scattered around Uranus after its formation.

Irregular Retrograde Moons (Outer Group)

Relatively small moons that orbit at distances between 4 million to 24 million kilometres from Uranus in inclined orbits between 141 to 170 degrees. They travel in an opposite direction to the rotation of Uranus and are probably objects that have been captured by Uranus.

Irregular Prograde Moons (Outer Group)

One moon, Margaret, which orbits at a distance of 14 million kilometres in an inclined orbit of 57 degrees and travels in the same direction of Uranus' rotation.

List of Uranus' Moons

Name of Moon	Diameter	Orbital Distance	Length of Orbit	Discovered	Discoverer	Group
Cordelia	40 km 25 miles	49,800 km 30,944 miles	8 hours	1986	Richard J. Terrile	Shepherd
Ophelia	43 km 27 miles	53,800 km 33,430 miles	9 hours	1986	Richard J. Terrile	Shepherd
Bianca	54 km 34 miles	59,200 km 36,785 miles	10 hours	1986	Bradford A. Smith	Portia
Cressida	82 km 51 miles	61,800 km 38,401 miles	11 hours	1986	Stephen P. Synott	Portia
Desdemona	70 km 44 miles	62,700 km 38,960 miles	11 hours	1986	Stephen P. Synott	Portia
Juliet	106 km 66 miles	64,400 km 40,016 miles	12 hours	1986	Stephen P. Synott	Portia
Portia	140 km 87 miles	66,100 km 41,073 miles	12 hours	1986	Stephen P. Synott	Portia
Rosalind	72 km 45 miles	69,900 km 43,434 miles	13 hours	1986	Stephen P. Synott	Portia
Cupid	18 km 11 miles	74,390 km 46,224 miles	15 hours	2003	Mark Robert Showalter, Jack Jonathan Lissauer	Portia
Belinda	90 km 56 miles	75,300 km 46,789 miles	15 hours	1986	Stephen P. Synott	Portia
Perdita	26 km 16 miles	76,420 km 47,485 miles	15 hours	1999	Erich Karkoschka	Portia
Puck	162 km 101 miles	86,000 km 53,438 miles	18 hours	1985	Stephen P. Synott	Inner
Mab	24 km 15 miles	97,740 km 60,733 miles	22 hours	2003	Mark Robert Showalter, Jack Jonathan Lissauer	Inner
Miranda	480 km 298 miles	129,900 km 80,716 miles	34 hours	1948	Gerard Kuiper	Major
Ariel	1,162 km 722 miles	190,900 km 118,620 miles	60 hours	1851	William Lassell	Major
Umbriel	1,169 km 726 miles	266,000 km 165,284 miles	99 hours	1851	William Lassell	Major
Titania	1,578 km 981 miles	436,300 km 271,104 miles	9 days	1787	William Herschel	Major
Oberon	1,523 km 946 miles	583,500 km 362,569 miles	13 days	1787	William Herschel	Major
Francisco	22 km 14 miles	4,276,000 km 2,656,978 miles	267 days	2003	Matthew J. Holman, Brett J. Gladman and teams	Retrograde
Caliban	72 km 45 miles	7,231,000 km 4,493,126 miles	579 days	1997	Brett J. Gladman, J. J. Kavelaars, Phillip D. Nicholson, Joseph A. Burns	Retrograde
Stephano	32 km 20 miles	8,004,000 km 4,973,445 miles	676 days	1999	Brett J. Gladman, J. J. Kavelaars, Matthew J. Holman, Jean-Mark Petit, Hans Scholl	Retrograde
Trinculo	18 km 11 miles	8,504,000 km 5,284,130 miles	758 days	2001	Matthew J. Holman and team	Retrograde
Sycorax	150 km 93 miles	12,179,000 km 7,567,665 miles	1283 days	1997	Brett J. Gladman, J. J. Kavelaars, Phillip D. Nicholson, Joseph A. Burns	Retrograde
Margaret	20 km 12 miles	14,345,000 km 8,913,553 miles	1695 days	2003	Scott S. Sheppard, David C. Jewitt	Prograde
Prospero	50 km 31 miles	16,256,000 km 10,100,991 miles	1977 days	1999	Brett J. Gladman, J. J. Kavelaars, Matthew J. Holman, Jean-Mark Petit, Hans Scholl	Retrograde
Setebos	48 km 30 miles	17,418,000 km 10,823,023 miles	2235 days	1999	Brett J. Gladman, J. J. Kavelaars, Matthew J. Holman, Jean-Mark Petit, Hans Scholl	Retrograde
Ferdinand	20 km 12 miles	20,901,000 km 12,987,254 miles	2823 days	2003	Matthew J. Holman and team	Retrograde

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