survey of astronomy astro1010-lee.com twlee2016@gmail.com chapter 13 uranus & neptune

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Chapter 13Uranus & Neptune

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Chapter 13Uranus 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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Chapter 13William 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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Chapter 13Most 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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Chapter 13During 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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Chapter 13As the Uranus axis of rotation lies almost in

the plane of its orbit , the seasonal variations are extreme

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Chapter 13Rings 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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Chapter 13The 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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Chapter 13

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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Chapter 13Neptune 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

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Chapter 13Details of Neptune cannot be made out

from Earth. The arrows point to the moons Triton and Nerid

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Chapter 13

Voyager found a Great Dark Spot. It was deter-mined 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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Chapter 13The rings of Neptune were discovered from the

Earth but they looked like arcs. Voyager found complete rings but some of them were ’lumpy’.

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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Chapter 13Two 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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Chapter 13

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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Chapter 13Nitrogen 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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Chapter 13

Uranus and Neptune are very similar.

Uranus NeptuneMass 14.5 × E 17.1 × E Radius 4.0 × E 3.9 × EDensity 1.3 x H2O 1.6 x H2O

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Chapter 13

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.

Uranus and Neptune both have substantial magnetic fields, but at a large angle to their rotation axes.

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Chapter 13Magnetic 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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Chapter 13

End of Chapter 13

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Chapter 13

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Chapter 13

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Chapter 13