Transcript astron_ch_7b

Sponge:
List the six
layers of
the Earth.
Atmosphere
A mixture of gases:
N2
78%
O2
21%
Ar
0.9%
CO2
0.03%
Water vapor in
the atmosphere
varies from
0.1% to 3%.
What makes Earth
unique is Oxygen.
The presence
of water and
carbon dioxide
is also important.
The atmosphere provides
oxygen, protects the Earth
from harsh solar and
cosmic radiation, keeps
most meteoroids from
becoming meteorites, and
keeps the Earth’s surface
warm.
The atmosphere is like a
protective blanket for the Earth.
The atmosphere
is relatively small,
half below 5 km,
99% below
30 km.
Density
and pressure
decrease steadily
with height.
Layers of atmosphere:
Troposphere - below 15 km
Stratosphere - 15 to 40-50 km
Mesosphere - 50 to 90 km
Thermosphere - above 90 km
Exosphere - above 250 km
The troposphere is the
area where convection
occurs.
This rising of warm air
and sinking of cooler air
is powered by the surface
heat of the Earth.
These convection
currents are
responsible for
all the weather
on Earth.
Temperature
decreases with
altitude in the
troposphere.
The top of the
troposphere is
the tropopause.
Above this, in the
stratosphere,
the air is still.
Within the
stratosphere,
the ozone layer
is found.
In the ozone layer
the temperature
increases as solar
UV radiation is
absorbed by O2,
O3 (ozone), and N2.
This absorption
of UV radiation
protects the Earth
from its effects.
The ozone layer stretches
into the mesosphere,
although the term
“stratosphere” is often
used to refer to both the
stratosphere and the
mesosphere.
In the thermosphere, the
temperature increases
with altitude because the
high-energy part of the
Sun’s spectrum splits
molecules into atoms
and atoms into ions.
This ionization of the
atmosphere is significant
above about 100 km.
This electrically
conductive part of the
atmosphere is called
the ionosphere.
This ionosphere
is part of the
thermosphere and
can actually reflect
certain radio
wavelengths. (AM)
The surface of the Earth
absorbs much energy from
the Sun and reradiates it.
Most of this energy escapes
into space, but infrared
radiation is partially blocked by
the carbon dioxide and water
vapor in the atmosphere.
This partial
blocking of solar
radiation is called
the greenhouse
effect.
Warmed air rises and is
replaced by air that has
been cooled in the upper
atmosphere. This
produces a circulation
pattern called a
convection cell.
This rising and falling
air affects atmospheric
heating and also produces
surface winds. Passenger
aircraft tend to fly above
these disturbances, in
the lower stratosphere.
The magnetosphere is
the region around the Earth
influenced by the Earth’s
magnetic field.
This field is similar to that
of a bar magnet roughly
aligned with the spin axis
of the Earth.
It was detected by satellites
launched in the late 1950’s.
It contains two doughnutshaped zones of high energy
particles (one about 3000 and
the other 20 000 km above the
Earth’s surface), called the
Van Allen Belts. The radiation
here is lethal.
The magnetic field is
believed to be caused
by rotating, conducting
material (molten iron
and nickel) flowing in the
Earth’s outer core. This is
called dynamo theory.
The high energy particles
in the Van Allen Belts are
collected from the solar
wind and are trapped
because they are charged
particles (primarily
protons and electrons).
These charged particles
often escape near the
poles, where the magnetic
field intersects the
atmosphere.
They rip apart air particles,
creating spectacular lights
called the aurora.
In the north, these
lights are called the
aurora borealis
(northern lights). In the
south, they are called
the aurora australis
(southern lights).
Aurorae as seen from ISS
Perseid meteor to the left
The Aurora Australis (from space)
Earth isn’t the only planet
to have aurorae. The next
three pictures are of
aurorae on Saturn. Notice
the strange hexagonal
shape on the last image.
The magnetic field is
distorted by the solar
wind. On the daytime
side of the Earth, the
magnetosphere is
compressed.
The boundary between
the magnetosphere and
the solar wind is called the
magnetopause and is
found about 10 Earth radii
from the Earth’s surface.
On the side opposite
the Sun, the field lines are
extended, often reaching
beyond the Moon’s orbit.
As a result the
magnetosphere is
“teardrop”-shaped.
The magnetosphere
screens out much
destructive radiation
from the solar winds.
In the year 2000, we were
at the peak of solar activity
and the highest solar
winds. If you fly 75,000 air
miles on passenger jets,
it is like being exposed to
20 X-ray procedures.