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Note: You can click on each image below to view a larger version.
Uranus
is another gas giant, but its composition differs from that of Jupiter
and Saturn. It lacks the massive
layer of liquid metallic hydrogen found in those planets, so its internal structure consists mainly of rock and ice
with only about 15% hyrdogen.
However, its gaseous outer layers are about 83% hydrogen, 15% helium, and 2% methane. |
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ABOVE RIGHT: Uranus as seen by Voyager 2, the only spacecraft to have visited it so far.
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Uranus has extensive rings, but because they consist of a dark material they are extremely hard to see and
were not discovered until 1977. Voyager 2 took this image while it was in the shadow of Uranus. The
exposure took 96 seconds, so the stars in the background appear as short streaks due to the movement
of the spacecraft. |
Visually, Uranus appeared bland, with pale blue clouds in which very few features could be seen. However more
recent pictures from the Hubble Space Telescope seem to show greater activity in the atmosphere, suggesting that
this varies from season to season.
Uranus,
Neptune and Pluto are the only three planets which were not
known in antiquity (although of course Pluto is no longer classified as a planet). All the others are so bright that early peoples could easily see that they changed their
position in the sky from night to night, and were thus somehow different from the other stars.
The word planet originally meant "wandering star."
Uranus was discovered in 1781 by William Herschel, who although originally from Hanover in Germany
spent much of his life in Bath, England. Herschel wasn't actually looking for a new planet, he simply came across
it while doing a survey of the sky, but the discovery was a sensation that made him extremely famous. He was also
the best telescope-maker of his day, which contributed a lot to his success as an astronomer. Some astronomers
had in fact seen Uranus before, but since their telescopes hadn't been powerful enough to show it as anything
other than a point of light they had assumed that it was just a star. Indeed, Herschel at first reported it as a
rather odd comet.
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Uranus
and its largest moons, all of which are named after characters in the plays of Shakespeare.
Clockwise from bottom left: Ariel, Umbriel, Oberon, Titania, Miranda. |
Miranda is a moon with a very unusual landscape, since it has such a huge variety of features:
cratered plains, ridges, valleys, and huge ice cliffs. The strangest of all are two areas of bizarre grooves and
ridges, nicknamed "the race-track" and "the chevron". It is not at all clear how such a jumble of terrain
could have come about, and it has even been suggested that Miranda may have been broken up by an impact and
then re-formed.
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| ABOVE: Two views of Miranda. The left-hand
picture shows "the race track" near the left edge, and "the chevron" just to the
right of centre. The proper names of these features are Inverness Corona and Arden Corona.
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