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Once considered one of the blander-looking
planets, Uranus (pronounced YOOR un nus) has been revealed
as a dynamic world with some of the brightest clouds
in the outer solar system and 11 rings. Uranus gets
its blue-green color from methane gas above the deeper
cloud layers (methane absorbs red light and reflects
blue light).
Uranus was discovered in 1781 by astronomer
William Herschel, who at first believed it to be a comet.
This seventh planet from the Sun is so distant that
it takes 84 years to complete an orbit.
Uranus is classified as a "gas giant"
planet because it has no solid surface. The atmosphere
of Uranus is hydrogen and helium, with a small amount
of methane and traces of water and ammonia. The bulk
(80 percent or more) of the mass of Uranus is contained
in an extended liquid core consisting primarily of "icy"
materials (water, methane, and ammonia), with higher-density
material at depth.
In 1986, Voyager 2 observed faint cloud
markings in the southern latitudes blowing westward
between 100 and 600 km/hr. In 1998, the Hubble Space
Telescope observed as many as 20 bright clouds at various
altitudes in Uranus' atmosphere. The bright clouds are
probably made of crystals of methane, which condense
as warm bubbles of gas well up from deep in the atmosphere
of Uranus.
Uranus currently moves around the Sun
with its rotation axis nearly horizontal with respect
to the ecliptic plane. This unusual orientation may
be the result of a collision with a planet-sized body
early in the planet's history, which apparently changed
Uranus' rotation radically. Uranus' magnetic field is
unusual in that the magnetic axis is tilted 60 degrees
from the planet's axis of rotation and is offset from
the center of the planet by one-third of the planet's
radius.
Uranus is so far from the Sun that, even
though tipped on its side and experiencing seasons that
last over twenty years, the temperature differences
on the summer and winter sides of the planet do not
differ that greatly. Near the cloudtops, the temperature
of Uranus is near -215 ÁC.
Uranus' rings were first discovered in
1977. The rings are in the planet's equatorial plane,
perpendicular to its orbit about the Sun. The 10 outer
rings are dark, thin, and narrow, while the 11th ring
is inside the other ten and is broad and diffuse. The
rings of Uranus are very different from those surrounding
Jupiter and
Saturn. When
viewed with the Sun behind the rings, fine dust can
be seen scattered throughout all of the rings.
Uranus has 21 known moons, named mostly
for characters from the works of Shakespeare and Alexander
Pope. Miranda is the strangest Uranian moon. The high
cliffs and winding valleys of the moon may indicate
partial melting of the interior, with icy material occasionally
drifting to the surface.
Related Links:
Source: NASA
Last Updated : 08.20.2003
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Discovered By:
William Herschel
Date of Discovery:
1781
Distance from the Sun:
(Semimajor axis of orbit)
2,870,972,200 km
19.19126393 A.U.
Radius:
25,559 km
(4.007 of Earth's radius)
Volume:
52 (Earth = 1)
Mass:
86.849 x 1027 g
Density:
1.30 gm/cm3
Surface Gravity:
869 cm/s2
Escape Velocity:
21.29 km/s
Sidereal Rotation Period:
0.71833 (retrograde)
Sidereal Orbit Period:
84.016846 sidereal years
Mean Orbit Velocity:
6.8352 km/s
Orbit Eccentricity:
0.04716771
Orbit Inclination:
0.76986 degrees
Equatorial Inclination:
97.86 degrees
Atmospheric Temperature (at level with
pressure = 1 bar):
76 K
Major Atmospheric Constituents:
H2, He, CH4
Natural Satellites:
1. Cordelia
2. Ophelia
3. Bianca
4. Cressida
5. Desdemona
6. Juliet
7. Portia
8. Rosalind
9. Belinda
10. Puck
11. Miranda
12. Ariel
13. Umbriel
14. Titania
15. Oberon
16. Caliban
17. Stephano
18. Trinculo
19. Sycorax
20. Prospero
21. Setebos
Uranus also has a provisional satellite,
1986 U10, whose orbit lies between those of Sycorax
and Prospero.
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