Download VII. Uranus - Napa Valley College

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VII.
Uranus
A.
Gas Giant
1.
Rings but not visible
2.
HUGE axial tilt 97E!
3.
Mostly hydrogen and helium
4.
Medium rotation rate
5.
Cold — 55 K at the cloud tops
B.
Physical characteristics
1.
Mass: 8.7 × 1025 kg
2.
Radius: 26,000 km
3.
Atmosphere: about 83% H, 15% He, traces of other gases
4.
Distance from Sun: 19.2 AU . 20 AU
5.
Rotation period: 17 hours
6.
Revolution period: 84 years
C.
Satellites
1.
25 known
2.
Most small; largest moderate in size
D.
Structure
1.
Interior
a.
Rocky core
b.
Compressed water
c.
Liquid hydrogen and helium
2.
No definite surface — gets thicker and thicker until solid
3.
Also storms.
VIII. Neptune
A.
Gas Giant - very similar to Uranus
1.
Rings but not visible
2.
Large axial tilt 30E
3.
Mostly hydrogen and helium
4.
Medium rotation rate
5.
Cold — 55 K at the cloud tops
B.
Physical characteristics
1.
Mass: 1 × 1026 kg
2.
Radius: 25,000 km
3.
Atmosphere: about 80% H, 20% He, traces of other gases
4.
Distance from Sun: 30 AU
5.
Rotation period: 16 hours
6.
Revolution period: 165 years
C.
Satellites
1.
13 known
2.
Most small; largest moderate in size
D.
Structure
1.
Interior
a.
Rocky core
b.
Compressed water
c.
Liquid hydrogen and helium
2.
No definite surface — gets thicker and thicker until solid
3.
Also storms.
IX.
X.
Dwarf Planets
A.
A planet is defined to be an object that is large enough to coalesce into a sphere and
to have cleared its orbit of other material.
B.
Under this definition, Pluto, which was a planet, is no longer considered to be one
— it lives in a region of ice objects called the Kuiper belt out beyond the orbit of
Neptune. It is spherical but has not cleared its orbit.
C.
The new object 2003UB313 or Eris is larger than Pluto and would have been a
planet if the definition hadn’t been changed.
D.
There may be as many as 20 Pluto-sized objects out beyond Neptune, and
astronomers wanted to keep the number of planets to a reasonable size.
E.
Under this definition, Ceres and other large objects that had been asteroids are now
dwarf planets as well.
F.
Notable Dwarf Planets
1.
Pluto
a.
One of the largest members of the Kuiper belt.
b.
Charon — its moon — large in comparison to Pluto’s size
c.
Huge tilt! — 118E
d.
Cold — 40 K
e.
Made of ices
f.
Mass — 1.3 × 1022 kg
g.
Radius — 1200 km
h.
Atmosphere
(1)
None to speak of except in “summer” when closest to Sun —
nitrogen and carbon monoxide
(2)
Shares its atmosphere with Charon
(3)
Double planet
i.
Distance from Sun — 40 AU
j.
Rotation period
(1)
6.4 days
(2)
Same as Charon’s
(3)
Same as orbital period around each other
(4)
Doubly tidally locked
k.
Revolution period — 250 years
l.
Surface: frozen nitrogen and CO
m.
Moons
(1)
Charon
(a)
Similar to Pluto
(b)
Surface — water ice
(2)
Two other tiny moons
2.
Eris — 2003UB313
a.
Similar to Pluto but larger
b.
Called Xena in house while analyzing after its discovery
c.
Has a moon that was called Gabrielle - Dysnomia.
Vagabonds of the Solar System
A.
Asteroids
1.
Too small to form as spheres
2.
Most orbit Sun between Mars and Jupiter — asteroid belt
3.
Probably prevented from forming a planet by Jupiter’s large gravitational
field
4.
Some exist elsewhere
a.
b.
c.
B.
C.
Jupiter’s Lagrange points — Trojan asteroids
Some cross Earth’s orbit — might hit us at some point
Collisions with such objects in the past may have caused mass
extinctions.
5.
Composition — mostly rock with some metal
Comets
1.
Dirty snowballs.
2.
Highly elliptical orbits — spend most of the time far from the Sun
3.
Kuiper Belt and Oort Cloud
4.
When close to Sun, heat sublimes gas from the comet creating a tail.
5.
Two tails — gas and dust
6.
Directed away from Sun
7.
May have provided Earth (and other planets) with water in the early solar
system.
8.
Also can collide with Earth to devastating effect
Meteoroids, Meteors, and Meteorites
1.
Meteoroid — small object floating through space
2.
Meteor — small object in the process of burning up in the Earth’s atmosphere
3.
Meteorite — small object that makes it through the Earth’s atmosphere and
hits the ground.
4.
Meteor Showers — debris left in orbit as comets move around intersect
Earth’s atmosphere creating as many as a meteor a second (rare) — usually a
meteor a minute or so.
5.
Types of meteorites
a.
Stony
(1)
Look like ordinary rocks.
(2)
If you see an “ordinary rock” lying atop the snow in the arctic or
antarctic, it’s a stony meteorite.
b.
Iron — easy to distinguish from ordinary rocks
c.
Stony-iron — roughly equal amounts of stone and iron
6.
Thought to come from asteroids
a.
Stony — from exterior
b.
Iron — from iron core
c.
Stony-Iron — from boundary between core and exterior
Chapter 7 — The Sun
Important numbers to know about the Sun:
1. Distance from Earth to Sun: 1 AU = 150 million km
2. Radius: 700,000 km
3. Surface Temperature: 5800 K
4. Mass: 2 × 1030 kg
5. Luminosity: 4 × 1026 watts
6. Mean density of the Sun = 1.4 times the density of water
7. Period of Rotation: 25 days
8. Core Temperature of the Sun: 15 million K
Outer Parts of the Sun
Photosphere:
1. Visible surface of the Sun
2. It is about 400 km thick
3. Its temperature ranges from 8000 K at the bottom to
5800 K at the top.
4. The photosphere has a mottled appearance called
granulation.
— These granules pop into existence and stay for about
15 minutes to a half an hour.
— Size: a few hundred km across.
— We see them because the hot interior is brighter than
the cool borders.
— Convection cells in the photosphere
(Aside — Modes of heat transport
1. Conduction: heat transport through solids. (Not
important in stars)
2. Convection — hot material moves from one place to
another carrying heat with it.
3. Radiation — heat transfer through a vacuum —
blackbody radiation.)
Chromosphere
1. Lowest part of the Sun’s “atmosphere.”
2. Directly above the photosphere and about 10,000 km thick
3. The temperature rises at its top to about 50,000 K
4. It is seen just as the photosphere is covered during a total eclipse of the Sun.
5. Its red color gives it its name.
6. Produces an emission spectrum meaning it is a dilute gas — helium discovered in its
spectrum.
7. Spicules — small jets into chromosphere from the photosphere
Corona
1. Outer part of the Sun’s “atmosphere.”
2. No definite end — gets thinner and thinner as you move away from the Sun.
3. Its temperature rises into the millions of K.
4. Outflow of energy from the photosphere drives charged particles in the Corona out into space
— called the solar wind.
5. Every once in a while a blob of matter is ejected from the corona — coronal mass ejection
Active Surface of the Sun
Sunspots
1. Storms on the Sun — magnetic storms not electrical
2. They are 1000 K to 2000 K cooler than the rest of the
surface — appear dark for that reason.
3. Sunspots appear in pairs or small groups.
4. Some of the spots in a group will have north magnetic
polarity while the remainder will have a south magnetic
polarity.
5. In a given hemisphere, say the northern, the western most spots might be magnetic north
poles with the eastern most spots being magnetic south poles.
6. If so, in the other hemisphere (here, the southern) the magnetic polarity is reversed with
eastern spots being magnetic north and western spots being magnetic south.
7. These magnetic polarities reverse periodically.
8. Sunspots have light borders called plages because they look like beaches around a lake.
9. Small filaments in the region are the places where the magnetic field is zero.
Cause of Sunspots
1. Sun has a strong magnetic field.
2. When the Sun’s magnetic field looks like that of a bar magnetic, we will call it a regular
magnetic field.
3. Because of all the charged particles in the material of
the Sun, these field lines get trapped in the Sun.
4. The Sun rotates at different rates at different
latitudes — faster at the equator. As it rotates the
magnetic field lines get distorted.
5. Sunspots form where this distorted field exits the
Sun.
6. As the field becomes more and more distorted, more
and more sunspots form.
7. As sunspot maximum, there are a lot of sunspots and they tend to reside at latitudes plus and
minus 20 degrees from the equator.
8. At sunspot minimum, the sunspots tend to reside at the equator.
9. Eventually, the field becomes so distorted that it breaks up and a new regular field is
produced.
10. It takes eleven years for the Sun to go from sunspot minimum through the cycle and back to
sunspot minimum.
11. Really a 22-year cycle — in alternate 11-year cycles, the sunspot magnetic polarity reverses.