Chapter 13
Survey of Astronomy
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Uranus & Neptune
Uranus was Discovered in 1781 by
William Herschel; first planet to be
discovered in recorded history.
Little detail can be seen
from Earth; arrows
point to three of
Uranus’s moons.
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William Herschel
Born in Germany he Anglicized his name when he
came to England with the Hanover Kings. He was a
musician from a musical family.
As an amateur Astronomer he looked at the sky with
telescopes he built himself. Among other things in
the sky he found what he thought was a comet.
After further study he realized he had found a
planet, the first in recorded history. Because of the
fame of that discovery he became the Court
Astronomer to King George III
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Most of the planets have their axes slightly
tipped with respect to the plane of their orbits.
Uranus is unusual in that it is tipped more than
90 degrees. As a result the rotation of the
planet is retrograde.
Here we see Earth
tipped 23.5
degrees and
Uranus is tipped
98 degrees
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During the Voyager
encounter in l985 we
only saw a featureless
face as the Sun shone on
the pole of the planet.
Several years later When
the HST looked at it we
could see stripes and
storms.
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As the Uranus axis of rotation lies almost in
the plane of its orbit , the seasonal
variations are extreme
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Rings around Uranus were discovered from Earth
and we saw 3 narrow rings and 2 broad rings. The
Voyager saw a system of hundreds of ringlets.
The streaks are
stars seen through
the Uranus broad
but thin ring
system
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The moon Miranda has
large chunks of rock and
large fields of ice. It
looks like it has been
shattered in the near
past and is now pulling
itself back together. All
of the parts have not yet
found their final places.
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The Titus-Bode Rule is
a handy approximation
to Keller's 3rd law to
demonstrate the
distances of the planets
from the Sun. It has no
scientific significance.
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Neptune was discovered 1846,
after analysis of Uranus’s orbit
indicated its presence. Any new
planet could not fit the Titus
Bode Rule, hence the
English and French
Astronomical Societies ruled
out another Planet. However,
an Englishman, Adams , and a
Frenchman, Le Verrier , gave
their calculations to a German,
John Gottfried Galle, who
found Neptune immediately
Details of Neptune cannot
be made out from Earth.
The arrows point to the
moons Triton and Nerid
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Voyager found a Great
Dark Spot. It was determined to be a large storm.
There were other smaller
storms.
Of special interest were the
fast moving white clouds,
demonstrating that the
winds were the fastest in
the Solar System.
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Neptune has five rings,
three narrow and two broad.
Our ring theories have been
badly stretched by these
rings. Rings do NOT seem to
obey any rules.
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The rings of Neptune were discovered from the
Earth but they looked like arcs. Voyager found
complete rings but some of them were ’lumpy’.
Two moons, Triton and Nerid, were discovered
from the Earth. Eleven more were found by
Voyager.
The moon of most interest is Triton. Triton is
unique in many ways. It’s temperature is the lowest
of any body in the Solar System that we have
visited, 32 deg. K. It has an atmosphere, high
winds, active geysers and evidence of plate
tectonics, frozen lakes and water volcanoes.
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Triton revolves around Neptune retrograde
and it rotates on its axis retrograde.
The tidal forces and
the retrograde
motion will one
day cause Triton to
crash into the
planet.
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Nitrogen geysers have
been observed on Triton,
contributing to the
surface features
Also, there appear to be frozen
water lakes and ice volcanoes
on Triton
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Uranus and Neptune are very similar.
Uranus Neptune
Mass 14.5 × E 17.1 × E
Radius 4.0 × E
3.9 × E
Density 1.3 x H2O 1.6 x H2O
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The rectangle within
each planet shows a
bar magnet that
would produce a
similar field. Note
that both Uranus’s
and Neptune’s are
significantly off
center.
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Uranus and Neptune both have substantial
magnetic fields, but at a large angle to their
rotation axes.
Magnetic fields of Uranus and Neptune must not
be produced by dynamos, as the other planets’
fields seem to be.
Interior structure of Uranus and Neptune,
compared to that of Jupiter and Saturn
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End of Chapter 13
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Chapter 13
Chapter 13
Survey of Astronomy
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Chapter 13
Survey of Astronomy
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Chapter 13
Survey of Astronomy
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