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Uranus is the seventh planet from the Sun and the third largest
(by diameter). Uranus is larger in diameter but smaller in
mass than Neptune.
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Orbit:
Diameter:
Mass:
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2,870,990,000 km (19.218 AU)
from the Sun
51,118 km (equatorial)
8.683e25 kg
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Astronomy
Uranus, the first planet discovered in modern times, was discovered
by William Herschel while he was systematically searching the sky
with his telescope on March 13, 1781. It had actually been seen
many times before but ignored as simply another star. The earliest
recorded sighting was in 1690 when John Flamsteed, the first Royal
Astronomer of England (who later provided Newton with the data from
which he verified his gravitational theory), cataloged it as 34
Tauri). Most of the planets spin on an axis nearly perpendicular
to the plane of the ecliptic but Uranus' axis is almost parallel
to the ecliptic, and for this reason it is sometimes called 'the
sideways planet'. One theory for its strange position is that it
was hit by a giant asteroid millions of years ago. When last seen,
Uranus' south pole was pointed almost directly at the Sun. This
results in the odd fact that its polar regions receive more energy
input from the Sun than do its equatorial regions. It is counterintuitive,
then, that Uranus is nevertheless hotter at its equator than at
its poles. The reason for this is unknown.
Like the other gaseous planets, Uranus has bands of clouds that
blow around rapidly. Uranus' blue color is the result of the absorption
of red light by methane in the upper atmosphere. There may be colored
bands like Jupiter's but they are hidden from view by the overlaying
methane layer.
Like the other gas planets, Uranus has rings, discovered by a team
of astronomers in 1977. Like Jupiter's, they are very dark but like
Saturn's they are composed of fairly large particles ranging up
to 10 meters in diameter as well as fine dust. Voyager 2 discovered
10 small moons in addition to the 5 large ones already known. It
is likely that there are several more tiny satellites within the
rings.
Uranus' magnetic field is odd in that it is not centered on the
center of the planet and is tilted almost 60 degrees with respect
to the axis of rotation. It is probably generated by motion at relatively
shallow depths within Uranus.
Uranus is sometimes hardly visible to the naked eye even on a very
clear night, though it is fairly easy to see with binoculars, provided
you know exactly where to look. A small astronomical telescope will
show a small disk.
If you would like to know more about the solar system, Starscine
suggests the following websites:
www.nineplanets.org
www.nasa.gov
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