Umbriel (moon)

Umbriel

Umbriel as seen by Voyager 2 in 1986
Discovery
Discovered by	William Lassell
Discovery date	October 24, 1851
Designations
Pronunciation	/ˈʌmbriəl/ UM-bree-əl[1]
Alternative names	Uranus II
Adjectives	Umbrielian
Orbital characteristics[2]
Semi-major axis	266 000 km
Eccentricity	0.0039
Orbital period	4.144 d
Inclination	0.128° (to Uranus's equator)
Satellite of	Uranus
Physical characteristics
Mean radius	584.7 ± 2.8 km (0.092 Earths)[3]
Surface area	4 296 000 km2 (0.008 Earths)[a]
Volume	837 300 000 km3 (0.0008 Earths)[b]
Mass	1.172 ± 0.135 × 1021 kg (2 × 10−4 Earths)[4]
Mean density	1.39 ± 0.16 g/cm3[4]
Surface gravity	0.2 m/s2 (~ 0.023 g)[c]
Escape velocity	0.52 km/s[d]
Rotation period	presumed synchronous[5]
Axial tilt	0[5]
Albedo	0.26 (geometrical) 0.10 (Bond)[6]
Surface temp. min mean max solstice[7] ? ~75 K 85 K
Apparent magnitude	14.5 (V-band, opposition)[8]
Atmosphere
Surface 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.

1. ↑ Cite error: The named reference dict-def was used but no text was provided for refs named (see the help page).
2. ↑ Cite error: The named reference orbit was used but no text was provided for refs named (see the help page).
3. ↑ Cite error: The named reference Thomas 1988 was used but no text was provided for refs named (see the help page).
4. ↑ ^{4.0 4.1} Cite error: The named reference Jacobson Campbell was used but no text was provided for refs named (see the help page).
5. ↑ ^{5.0 5.1} Cite error: The named reference Smith Soderblom was used but no text was provided for refs named (see the help page).
6. ↑ Cite error: The named reference Karkoschka 2001, Hubble was used but no text was provided for refs named (see the help page).
7. ↑ Cite error: The named reference Grundy Young was used but no text was provided for refs named (see the help page).
8. ↑ Cite error: The named reference NASAspp was used but no text was provided for refs named (see the help page).