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Uranus and Neptune
Uranus – The Discovery
Discovered in 1781 by William Herschel.
 He wanted to name the planet “Sidus
Georgium” after the king of England.
 Thankfully, another astronomer talked him
out of it and he went with a name from
Greco-Roman mythology.

Where can you see it?

Barely visible to the naked eye, if you
know where to look. Few people see it
without a telescope.
Uranus: Physical Properties
Radius: 4.0 x that of Earth
 Mass: 14.5 x that of Earth
 Rotation: 17.2 hours
 Revolution: 84 years
 Distance: 19 AU
 Experiences differential rotation
 Axis of rotation: 98˚ - appears to “roll”
around the sun – sometimes its axis is
pointed toward the sun
 No internal heat source.

Strange times on Uranus
During summer in the northern
hemisphere, an observer would see the
sun make circles in the sky
 As summer turned into fall and then into
winter, eventually the sun would “fail” to
rise!

The Discovery of Neptune
Discovered because it “perturbed” Uranus’
orbit.
 Its position was mathematically calculated
by two people before it was discovered.
 The person who first found it did not get
credit for its discovered – the two
mathematicians that calculated it did.
 Actually, according to his notes, Galileo
may have seen it first – he just didn’t know
what it was at the time.

Neptune: Physical Properties
Period of revolution: 163.7 years (has not
made a complete orbit since its discovery
– it will in two years!)
 Distance from sun: 30.1 AU
 Cannot be seen with the naked eye. You
must have a telescope.
 Radius: 3.9 x that of Earth
 Mass: 17.1 x that of Earth

Neptune: Physical Properties,
cont.
Experiences differential rotation –
atmosphere rotates more slowly than the
planet.
 Rotational period: 16.1 hours.
 Tilt of axis: 29.6˚
 Radiates 2.7 times more heat than it
receives from the sun – scientists are not
sure why.

Atmospheres of Uranus and
Neptune
Similar to Jupiter and Saturn.
 Made up of hydrogen, helium, and
methane; contains very little ammonia.
 The more methane, the bluer the planet.
 Uranus is bluish green, while Neptune is
blue.
 Neptune had the “Great Dark Spot” –
located near the equator and about the
size of Earth. It has now vanished.
 Overall, both have stormy weather.

Uranian Clouds
Neptune’s Great Dark Spot
Magnetospheres and Interiors
Both planets have a magnetosphere.
 Both have large rocky cores about the size
of Earth, perhaps 10 times more massive.

Uranus’s Moons
Current count: 27
 Largest two were discovered by Herschel:
Titania and Oberon
 Others include Arial, Umbrial, Miranda.
 They are darker than Saturn’s moons.
 Miranda has many geological features:
faults, ridges, valleys, etc. It is considered
to be a tortured world.

Miranda
Titania
Neptune’s Moons
Current count: 13
 Only two can be seen from Earth – Triton
and Nereid.
 Most have retrograde orbits.

Neptune’s Moon Triton
6th largest moon in the solar system.
 Has a retrograde orbit.
 Has an atmosphere of nitrogen (100 times
thinner than Earth).
 Contains very few craters, which may be a
sign of tectonic activity.
 Contains large fissures.
 Contains frozen lakes of water.
 Voyager 2 detected possible nitrogenspewing geysers.

Neptune and Triton
More of Triton
It may be a “captured” moon.
 Is actually spiraling toward Neptune.
 Will eventually be torn apart by Neptune’s
gravity.

Triton
Rings
Both Uranus and Neptune have rings.
 Uranus’s were discovered during a “stellar
occultation” – a star passed behind them.
 They are different from those of Saturn.
They are dark, narrow, and widely spaced.
 Some of Uranus’s moons act as shepherd
satellites.
 Neptune’s rings have “clumped” areas.
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