Download Today`s Powerpoint - Physics and Astronomy

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Homework:
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Homework assignments for Chs 4 & 5 will post tomorrow
Cannot do homework without Mastering Astronomy
Homework counts for 22% of your grade
NOT DOING HOMEWORK REDUCES YOUR CHANCES OF A
GOOD GRADE IN THIS CLASS
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Question 7
Most asteroids
are found
a) beyond the orbit of Neptune.
b) between Earth and the Sun.
c) between Mars and Jupiter.
d) in the orbit of Jupiter, but 60 degrees ahead or
behind it.
e) orbiting the jovian planets in captured,
retrograde orbits.
Question 7
Most asteroids
are found
a) beyond the orbit of Neptune.
b) between Earth and the Sun.
c) between Mars and Jupiter.
d) in the orbit of Jupiter, but 60 degrees ahead or
behind it.
e) orbiting the jovian planets in captured,
retrograde orbits.
The Asteroid Belt is located
between
2.1 and 3.3 A U
from the Sun.
The Structure of the Solar System
L3
L5
L4
~ 5 AU
~ 45 AU
Lagrange Points
Interplanetary Matter: Asteroids
The inner solar
system, showing
the asteroid belt,
Earth-crossing
asteroids, and
Trojan asteroids
Interplanetary Matter: Asteroids
Large picture:
The path of
Icarus, an Earthcrossing asteroid
Inset: Ceres, the
largest asteroid
Interplanetary Matter: Asteroids
Asteroids and meteoroids have rocky composition;
asteroids are bigger.
(below)
Asteroid
Gaspra
(above) Asteroid
Ida with its
moon, Dactyl
(above)
Asteroid
Mathilde
Interplanetary Matter: Asteroids
Asteroid Eros
Interplanetary Matter: Comets
Comets are icy, with some rocky parts.
The basic components of a comet
Interplanetary Matter: Comets
The solar wind means the
ion tail always points away
from the Sun.
The dust tail also tends to
point away from the Sun,
but the dust particles are
more massive and lag
somewhat, forming a
curved tail.
Interplanetary Matter: Comets
The internal structure of the cometary nucleus
Oort Cloud
The size, shape, and orientation of cometary orbits
depend on their location. Oort cloud comets rarely
enter the inner solar system.
Meteor Showers
Meteor showers are
associated with comets –
they are the debris left
over when a comet
breaks up.
Meteor Showers
Question 9
Compared to
asteroids, comets
show all of these
properties EXCEPT
a)
b)
c)
d)
their densities are higher.
their orbits tend to be more elliptical.
they tend to be made of ice.
they can look fuzzy, whereas asteroids
appear as moving points of light.
e) their average distances from the Sun are
far greater.
Question 9
Compared to
asteroids, comets
show all of these
properties EXCEPT
a)
b)
c)
d)
their densities are higher.
their orbits tend to be more elliptical.
they tend to be made of ice.
they can look fuzzy, whereas asteroids
appear as moving points of light.
e) their average distances from the Sun are
far greater.
Comets have densities much
lower than asteroids or
planets.
Question 10
What causes a
meteor shower?
a) A comet and an asteroid collide.
b) Earth runs into a stray swarm of asteroids.
c) Earth runs into the debris of an old comet
littering its orbit.
d) Meteorites are ejected from the Moon.
e) Debris from a supernova enters Earth’s
atmosphere
Question 10
What causes a
meteor shower?
a) A comet and an asteroid collide.
b) Earth runs into a stray swarm of asteroids.
c) Earth runs into the debris of an old comet
littering its orbit.
d) Meteorites are ejected from the Moon.
e) Debris from a supernova enters Earth’s
atmosphere
Meteor showers can
generate a few
shooting stars, to
hundreds of
thousands, seen in
an hour.
Chapter 5: The Earth
Pale Blue Dot
Earth as seen from Voyager 1,
when it was 6 billion km from
home.
General Features
Mass: MEarth = 6 x 1027 g
Radius: REarth = 6378 km
Density: p = 5.5 g/cm3
Age: 4.6 billion years
Earth's Internal Structure
How do we know? Earthquakes. See later
Crust: thin. Much Si and Al
(lots of granite). Two-thirds
covered by oceans.
Mantle is mostly solid, mostly
basalt (Fe, Mg, Si). Cracks in
mantle allow molten material
to rise => volcanoes.
Core temperature is 6000 K.
Metallic - mostly nickel and
iron. Outer core molten, inner
core solid.
Atmosphere very thin
Earth's Atmosphere
78% Nitrogen
21% Oxygen
Original gases disappeared. Atmosphere is
mostly due to volcanoes and plants!
gas is ionized by
solar radiation
ozone is O3 , which
absorbs solar UV
efficiently, thus
heating stratosphere
commercial jet
altitudes
temperature on a cool day
Ionosphere
Particles in the upper reaches of the atmosphere are ionized by the sun.
Radio signals below ~20 MHz can “bounce” off the ionosphere allowing
Communication “over the horizon” (or mountains)
Earthquakes
They are vibrations in the solid Earth, or seismic waves.
Two kinds go through Earth, P-waves ("primary") and S-waves ("secondary"):
How do they measure where Earthquakes are centered?
seismic stations
*
*
*
Like all waves, seismic waves bend when they encounter changes in
density. If density change is gradual, wave path is curved.
S-waves are unable to travel in liquid.
Thus, measurement of seismic wave gives info on density of Earth's
interior and which layers are solid/molten.
Zone with no S waves:
must be a liquid core
that stops them
But faint P waves
seen in shadow zone,
refracting off dense
inner core
No P waves too:
they must bend sharply
at core boundary
Curved paths of
P and S waves:
density must slowly
increase with depth
Earth's Interior Structure
Average density
5.5 g/cm3
Crust
Mantle
Core
3 g/cm3
5 g/cm3
11 g/cm3
Density increases with depth => "differentiation"
Earth must have been molten once, allowing denser
material to sink, as it started to cool and solidify.
Earthquakes and volcanoes are related, and also don't occur at random
places. They outline plates.
Plates moving at a few cm/year. "Continental drift" or "plate tectonics"
When plates meet...
1) Head-on collision
(Himalayas)
side view
2) "Subduction zone"
(one slides under the other)
(Andes)
3) "Rift zone"
(two plates moving apart)
(Mid-Atlantic Ridge)
4) They may just slide past each other
(San Andreas Fault)
top view
=> mountain ranges, trenches, earthquakes, volcanoes
Clicker Question:
Sunlight absorbed by the Earth’s surface is
reemitted in the form of?
A: radio waves
B: infrared radiation
C: visible radiation
D: ultraviolet radiation
E: X-ray radiation
The Mid-Atlantic Ridge is a
rift zone.
What causes the drift?
Convection! Mantle slightly fluid and can support convection.
Plates ride on top of convective cells. Lava flows through cell
boundaries. Earth loses internal heat this way.
Cycles take ~108 years.
Plates form lithosphere (crust and solid upper mantle).
Partially melted, circulating part of mantle is asthenosphere.
Pangaea Theory: 200 million years ago, all the continents
were together!