Oberon (moon)

The best Voyager 2 image of Oberon
Size comparison of Earth, the Moon, and Oberon.
A photo of Oberon. All named surface features are captioned.

Outermost major moon of the planet Uranus.

- Oberon (moon)
The best Voyager 2 image of Oberon

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Uranus and its six largest moons compared at their proper relative sizes and in the correct order. From left to right: Puck, Miranda, Ariel, Umbriel, Titania, and Oberon

Moons of Uranus

Uranus, the seventh planet of the Solar System, has 27 known moons, most of which are named after characters that appear in, or are mentioned in, the works of William Shakespeare and Alexander Pope.

Uranus, the seventh planet of the Solar System, has 27 known moons, most of which are named after characters that appear in, or are mentioned in, the works of William Shakespeare and Alexander Pope.

Uranus and its six largest moons compared at their proper relative sizes and in the correct order. From left to right: Puck, Miranda, Ariel, Umbriel, Titania, and Oberon
The number of moons known for each of the four outer planets up to October 2019. Uranus currently has 27 known satellites.
The relative masses of the Uranian moons. The five rounded moons vary from Miranda at 0.7% to Titania at almost 40% of the total mass. The other moons collectively constitute 0.1%, and are barely visible at this scale.
Schematic of the Uranian moon–ring system
The five largest moons of Uranus compared at their proper relative sizes and brightnesses. From left to right (in order of increasing distance from Uranus): Miranda, Ariel, Umbriel, Titania, and Oberon.
Artist's conception of the Sun's path in the summer sky of a major moon of Uranus (which shares Uranus's axial tilt)
Irregular moons of Uranus. The X axis is labeled in Gm (million km) and in the fraction of the Hill sphere's radius. The eccentricity is represented by the yellow segments (extending from the pericentre to the apocentre) with the inclination represented on the Y axis.

William Herschel discovered the first two moons, Titania and Oberon, in 1787.

The Reconciliation of Titania and Oberon by Joseph Noel Paton

Oberon

King of the fairies in medieval and Renaissance literature.

King of the fairies in medieval and Renaissance literature.

The Reconciliation of Titania and Oberon by Joseph Noel Paton
One of William Blake's illustration to his The Song of Los, scholars have traditionally identified the figures as Titania and Oberon, though not all new scholarship does. This copy, currently held by the Library of Congress, was printed and painted in 1795.
Illustration of Oberon enchanting Titania by W. Heath Robinson, 1914

On January 11, 1787 William Herschel discovered both the outermost major satellite of Uranus, along its overall largest. In 1852, his son John Herschel named them Oberon and Titania, respectively.

1785 portrait by Lemuel Francis Abbott

William Herschel

German-born British astronomer and composer.

German-born British astronomer and composer.

1785 portrait by Lemuel Francis Abbott
Original manuscript of Symphony No. 15 in E-flat major (1762)
Replica in the William Herschel Museum, Bath, of a telescope similar to that with which Herschel discovered Uranus
Herschel's mirror polisher, on display in the Science Museum, London
Uranus, discovered by Herschel in 1781
NGC 2683 is an unbarred spiral galaxy discovered by William Herschel on 5 February 1788
William and Caroline Herschel polishing a telescope lens (probably a mirror); 1896 lithograph
The 40-foot (12 m) telescope
A Cassini orbiter's view of Mimas, a moon of Saturn discovered by Herschel in 1789.
William Herschel's model of the Milky Way, 1785
William Herschel's coat of arms deemed a notorious example of debased heraldry: Argent, on a mount vert a representation of the 40 ft. reflecting telescope with its apparatus proper on a chief azure the astronomical symbol of Uranus irradiated or. Crest: A demi terrestrial sphere proper thereon an eagle, wings elevated or
William Herschel, portrait by James Sharples, c. 1805

Other work included an improved determination of the rotation period of Mars, the discovery that the Martian polar caps vary seasonally, the discovery of Titania and Oberon (moons of Uranus) and Enceladus and Mimas (moons of Saturn).

Drawing of John Herschel, published in 1846

John Herschel

English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint, and did botanical work.

English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint, and did botanical work.

Drawing of John Herschel, published in 1846
A Calotype of a model of the lunar crater Copernicus, 1842
Disa cornuta (L.) Sw. by Margaret & John Herschel
Herschel's first glass-plate photograph, dated 9 September 1839, showing the mount of his father's 40-foot telescope
Portrait of John Herschel
1867 photograph by Julia Margaret Cameron
Margaret Brodie Stewart by Alfred Edward Chalon 1829
John Frederick William Herschel by Alfred Edward Chalon 1829
The adjoining tombs of John Herschel and Charles Darwin in Westminster Abbey.
Description of a machine for resolving by inspection certain important forms of transcendental equations, 1832

A few years later, in 1852, he proposed the names still used today for the four then-known satellites of Uranus: Ariel, Umbriel, Titania, and Oberon.

Photograph of Uranus in true colour (by Voyager 2 in 1986)

Uranus

Seventh planet from the Sun.

Seventh planet from the Sun.

Photograph of Uranus in true colour (by Voyager 2 in 1986)
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Simulated Earth view of Uranus from 1986 to 2030, from southern summer solstice in 1986 to equinox in 2007 and northern summer solstice in 2028.
Size comparison of Earth and Uranus
Diagram of the interior of Uranus
Uranus's atmosphere taken during the Outer Planet Atmosphere Legacy (OPAL) program.
Aurorae on Uranus taken by the Space Telescope Imaging Spectrograph (STIS) installed on Hubble.
The magnetic field of Uranus
(animated; 25 March 2020)
The first dark spot observed on Uranus. Image obtained by the HST ACS in 2006.
Uranus in 2005. Rings, southern collar and a bright cloud in the northern hemisphere are visible (HST ACS image).
Major moons of Uranus in order of increasing distance (left to right), at their proper relative sizes and albedos (collage of Voyager 2 photographs)
Uranus's aurorae against its equatorial rings, imaged by the Hubble telescope. Unlike the aurorae of Earth and Jupiter, those of Uranus are not in line with its poles, due to its lopsided magnetic field.
Crescent Uranus as imaged by Voyager 2 while en route to Neptune

With a large telescope of 25 cm or wider, cloud patterns, as well as some of the larger satellites, such as Titania and Oberon, may be visible.

Voyager 2 image of Titania's southern hemisphere

Titania (moon)

Largest of the moons of Uranus and the eighth largest moon in the Solar System at a diameter of 1578 km. Discovered by William Herschel in 1787, it is named after the queen of the fairies in Shakespeare's A Midsummer Night's Dream.

Largest of the moons of Uranus and the eighth largest moon in the Solar System at a diameter of 1578 km. Discovered by William Herschel in 1787, it is named after the queen of the fairies in Shakespeare's A Midsummer Night's Dream.

Voyager 2 image of Titania's southern hemisphere
Size comparison of Earth, the Moon, and Titania.
Voyager 2's highest-resolution image of Titania shows moderately cratered plains, enormous rifts and long scarps. Near the bottom, a region of smoother plains including the crater Ursula is split by the graben Belmont Chasma.
Titania with surface features labeled. The south pole is situated close to the unidentified bright crater below and left of the crater Jessica.
Messina Chasma—a large canyon on Titania

It is covered with numerous impact craters reaching up to 326 km in diameter, but is less heavily cratered than Oberon, outermost of the five large moons of Uranus.

Umbriel as seen by Voyager 2 in 1986. At the top is the large crater Wunda, whose walls enclose a ring of bright material.

Umbriel (moon)

Moon of Uranus discovered on October 24, 1851, by William Lassell.

Moon of Uranus discovered on October 24, 1851, by William Lassell.

Umbriel as seen by Voyager 2 in 1986. At the top is the large crater Wunda, whose walls enclose a ring of bright material.
Size comparison of Earth, the Moon, and Umbriel.
False color image of Umbriel showing polygons
The Voyager 2 spacecraft

Covered by numerous impact craters reaching 210 km in diameter, Umbriel is the second most heavily cratered satellite of Uranus after Oberon.

Map of Coprates quadrangle showing details of Valles Marineris, the largest canyon system in the solar system. Some of the canyons may have once been filled with water.  The map shows the locations of a number of major Chasma.

Chasma

Deep, elongated, steep-sided depression.

Deep, elongated, steep-sided depression.

Map of Coprates quadrangle showing details of Valles Marineris, the largest canyon system in the solar system. Some of the canyons may have once been filled with water.  The map shows the locations of a number of major Chasma.
False color image of Candor Chasma showing locations of hydrated sulfate deposits, as seen by THEMIS. Red colors show rocky places.  Greens and blues show sandy, dusty areas.
Melas Chasma, as seen by THEMIS. Click on image to see relationship of Melas to other features.
Cliff in Candor Chasma Plateau, as seen by THEMIS. Click on image to see relationship with other features in Coprates quadrangle.
Cliff in northern wall of Ganges Chasma, as seen by THEMIS. Click on image to see relationship with other features in the Coprates quadrangle.
Ophir Chasma Wall, as seen by HiRISE.
Ius Chasma, as seen by HiRISE. Click on image to see layers.
Tithonium Chasma Layers, as seen by HiRISE.
Ganges Chasma Layers, as seen by HiRISE.

As of 2020, the IAU has named 122 such features in the Solar System, on Venus (63), Mars (25), Saturn's satellites Mimas (6), Tethys (2), Dione (8) and Rhea (5), Uranus's satellites Ariel (7), Titania (2) and Oberon (1) and Pluto's satellite Charon (3).

Ariel in greyscale by Voyager 2 in 1986. Numerous graben are visible, including the Kachina Chasmata canyon system stretching across the upper part of the image.

Ariel (moon)

Fourth-largest of the 27 known moons of Uranus.

Fourth-largest of the 27 known moons of Uranus.

Ariel in greyscale by Voyager 2 in 1986. Numerous graben are visible, including the Kachina Chasmata canyon system stretching across the upper part of the image.
Size comparison of Earth, the Moon, and Ariel.
The highest-resolution Voyager 2 color image of Ariel. Canyons with floors covered by smooth plains are visible at lower right. The bright crater Laica is at lower left.
Graben (chasmata) near Ariel's terminator. Their floors are covered by smooth material, possibly extruded from beneath via cryovolcanism. Several are cut by sinuous central grooves, e.g. Sprite and Leprechaun valles above and below the triangular horst near the bottom.
False-color map of Ariel. The prominent noncircular crater below and left of center is Yangoor. Part of it was erased during formation of ridged terrain via extensional tectonics.
HST image of Ariel transiting Uranus, complete with shadow

Although William Herschel, who discovered Uranus's two largest moons Titania and Oberon in 1787, claimed to have observed four additional moons, this was never confirmed and those four objects are now thought to be spurious.

Cassini mosaic of Rhea

Rhea (moon)

Second-largest moon of Saturn and the ninth-largest moon in the Solar System.

Second-largest moon of Saturn and the ninth-largest moon in the Solar System.

Cassini mosaic of Rhea
Giovanni Domenico Cassini, discoverer of Rhea in 1672
Size comparison of Earth (right), the Moon (left top), and Rhea (left down)
Surface features on Rhea well defined due to the lighting.
Closeup showing two craters on Rhea's surface taken in 2013 by Cassini spacecraft.
An artist's impression of Rhea's rings
Cassini color image of Rhea - large crater Powehiwehi (right center) - chasmata stretch vertically above (past crater Wakonda, near the terminator) - Onokoro Catenae (lower left).
Image of the wispy hemisphere, showing ice cliffs - Powehiwehi (upper center); chasmata stretch from upper left to right center - Onokoro Catenae (lower right).
View of Rhea's leading hemisphere with crater Inktomi and its prominent ray system just below center; impact basin Tirawa is at upper left
Enhanced-color views of Rhea taken by Cassini on 9 February 2015
Rhea's horizon viewed on 10 February 2015.

Indeed, Oberon, the second-largest moon of Uranus, has almost the same size, but is significantly denser than Rhea (1.63 vs 1.24) and thus more massive, although Rhea is slightly larger by volume.