Umbriel (moon) facts for kids

Kids Encyclopedia Facts
Umbriel as seen by Voyager 2 in 1986
Discovered by William Lassell
Discovery date October 24, 1851
How to say it /ˈʌmbriəl/ UM-bree-əl
Other names Uranus II
Adjective Umbrielian
Longest distance from the center of its orbital path
("semi-major axis")
266 000 km
How long it takes to complete an orbit 4.144 d
Angle above the reference plane
0.128° (to Uranus's equator)
What it orbits Uranus
Size and other qualities
Average radius 584.7 ± 2.8 km (0.092 Earths)
Surface area 4 296 000 km2 (0.008 Earths)
Volume 837 300 000 km3 (0.0008 Earths)
Mass 1.172 ± 0.135 × 1021 kg (2 × 10−4 Earths)
Average density 1.39 ± 0.16 g/cm3
Surface gravity 0.2 m/s2 (~ 0.023 g)
Escape velocity 0.52 km/s
Rotation period presumed synchronous
Angle at which it turns
(in relation to its orbit)
How much light it reflects
  • 0.26 (geometrical)
  • 0.10 (Bond)
Surface temp. Min. Avg. Max.
solstice ? ~75 K 85 K
Seeming brightness
("apparent magnitude")
14.5 (V-band, opposition)
Pressure zero

Umbriel is a moon of Uranus found on October 24, 1851 by William Lassell. It was found at the same time as Ariel.

Physical characteristics

So far the only close-up images of Umbriel are from the Voyager 2 probe, which made observations of the moon during its Uranus flyby in January, 1986. During the flyby the southern hemisphere of the moon was pointed towards the Sun so only it was studied.

Umbriel's surface is the darkest of the Uranian moons, and reflects only about half as much light as Ariel, Uranus' brightest moon. It has far more and bigger craters than do Ariel and Titania and is also the least geologically active. It is mostly made of water ice, with the balance made up of silicate rock, and other ices such as methane. Methane can break down and form reddish-black organic compounds such as tholins when bombarded by high-energy particles. Near-IR spectra of Ariel and Umbriel clearly show that water ice dominates the spectra of these objects.


Craters on Umbriel are named after many different demons from various mythologies.

Crater Named after
Alberich Alberich (Norse)
Fin Fin (Danish)
Gob Gob (Pagan)
Kanaloa Kanaloa (Polynesian)
Malingee Malingee (Australian Aboriginal mythology)
Minepa Minepa (Makua people of Mozambique)
Peri Peri (Persian)
Setibos Setebos (Patagonian)
Skynd Skynd (Danish)
Vuver Vuver (Finnish)
Wokolo Wokolo (Bambara people of West Africa)
Wunda Wunda (Australian Aboriginal mythology)
Zlyden Zlyden (Slavic)

Images for kids

Umbriel (moon) Facts for Kids. Kiddle Encyclopedia.