Lecture 11
THE SUN II
Interior and Solar Wind
Announcements
• Test 2 is one week from tonight.
– Similar format to test 1
– More info next time
• Don’t forget the eclipse at sunset on Saturday.
– Best viewing will be between 6:40 and 7:10.
– Moon will be in Earth’s outer shadow until 8:25
– Turn in your description (including a sketch or
photo) Monday for Bonus.
Solar Structure
• THE SOLAR ATMOSPHERE
–
–
–
–
Solar Wind
Corona
Chromosphere
Photosphere
The “Surface” of the Sun
• THE SOLAR INTERIOR
– The Convection Zone
– The Radiative Zone
– The Core
Daily Grade 11 – Question 1
Which outer layer of the Sun gets its name
from its reddish color visible during a total
solar eclipse?
A.
B.
C.
D.
Photosphere
Chromosphere
Corona
Reddishsphere
The Solar Wind
• Earth and all the planets in
the Solar System are
immersed in the Sun's
expanding outer atmosphere.
• This out flowing of solar
material (10 million tons per
year) is called the solar wind.
• Spacecraft measurements
show that the solar wind is
fast (400 km/s, about a
million miles per hour), thin
(a few particles per cubic
centimeter), and hot (several
hundred thousand degrees).
Coronal Holes
X-ray images of
the sun reveal
coronal holes.
These arise at
the foot points of
open field lines
and are the
origin of the
solar wind.
The Solar Sea
• The solar wind is an example of a plasma,
meaning its atoms are divided into electrically
charged particles - electrons, protons, and other
ions.
• This allows it to carry with it magnetic fields from
the corona which interact with the Earth's
magnetic field.
• Most of the solar wind particles are deflected by
the Earth's magnetic field, but some of these
charged particles leak into the terrestrial
environment.
The Sun-earth Connection
The Sun interacts with the Earth
directly with its:
• electromagnetic radiation
• charged particles (solar wind)
• magnetic field
Genesis Spacecraft
• While the spacecraft
was in orbit, it
collected particles of
the solar wind in
specially designed
high purity wafers.
• After two years, the
sample collectors
were re-stowed and
returned to Earth.
Genesis Spacecraft
• Although the parachute
did not deploy, some
collectors survived.
• The samples will be
stored and cataloged
under ultra-pure clean
room conditions and
made available to the
world scientific
community for study.
Daily Grade 11 – Question 2
Genesis was a sample return mission. What
did it return samples of?
A.
B.
C.
D.
A Comet
The Sun
Galactic Cosmic Rays
Mars
The Solar Interior
• Astronomers assume that the Sun is neither
expanding nor contracting (hydrostatic
equilibrium), not heating up or cooling down
(thermal equilibrium), and is spherically
shaped.
• Given these assumptions and knowledge of the
Sun's chemical composition and surface
temperature and pressure, it is possible to use
high-speed computers to calculate a model for
the solar interior, giving changing pressure and
temperature conditions.
The Origin Of Solar Energy
• COMBUSTION. Given the mass of the Sun and the rate at which
it is producing energy, if it were composed of coal or wood it would
burn out in about 3,000 years.
• GRAVITATIONAL COLLAPSE. Given the size and mass of the
Sun, if it were slowly collapsing, it would remain hot for about 20
million years. But geologists estimate the age of the Solar System
to be about 4.5 billions years.
• NUCLEAR FUSION. Given the Sun's abundance of hydrogen
and intense core temperature and pressure, conditions are
favorable for the fusion of hydrogen into helium. The Sun could
continue its present energy production for about 5 billion years
using this fusion process. In this process mass is converted into
energy according to Einstein's famous equation:
E = mc2
Nuclear Fusion Energy
Energy generation in the sun
(and all other stars):
Nuclear Fusion
= fusing together 2 or more
lighter nuclei to produce
heavier ones.
Nuclear fusion can
produce energy up to the
production of iron;
For elements heavier than
iron, energy is gained by
nuclear fission.
Binding energy
due to strong
force = on short
range, strongest
of the 4 known
forces:
electromagnetic,
weak, strong,
gravitational
Nuclear Fusion
• When 1,000 grams of
hydrogen are converted
into 993 grams of
helium, the 7 grams of
mass left over is
equivalent to the energy
of 200 tons of coal!
• The Sun converts over
600 million tons of
hydrogen into helium
every second, and 22
million tons of mass are
converted into energy.
Energy Generation in the Sun: The ProtonProton Chain
Basic reaction:
4 1H  4He + energy
4 protons have
0.048*10-27 kg (= 0.7 %)
more mass than 4He.
 Energy gain = Dm*c2
= 0.43*10-11 J
per reaction.
Need large proton speed ( high
temperature) to overcome
Coulomb barrier (electromagnetic
repulsion between protons).
T ≥ 107 K =
10 million K
Daily Grade 11 – Question 3
How does the sun maintain its energy output?
A.
B.
C.
D.
Gravitational contraction.
Fusion of hydrogen nuclei.
The impact of small meteoroids.
Fission of Uranium 235.
Energy Transport
• It takes nearly a million years for a
photon of light to make its way from the
core to the Sun's surface.
• The energy is radiated from the core to
near the surface in a random walk
fashion, then it is transported by
convection to the surface.
• The tops of the convection cells are seen
as solar granules.
• After reaching the photosphere, it is
radiated through interplanetary space
and beyond.
• Then it only takes 8.3 minutes to reach
the Earth.
Probing The Solar Interior
• Solar Seismology
• Solar Neutrinos
Helioseismology
• The Sun vibrates at a number of
different frequencies - sun
quakes.
• Because the vibrations are
effected by its internal structure,
solar oscillations can be used to
study the Sun's interior.
Helioseismology
The solar interior is opaque
(i.e. it absorbs light) out to the
photosphere.
 Only way to investigate
solar interior is through
Helioseismology
= analysis of vibration
patterns visible on the
solar surface:
Approx. 10
million wave
patterns!
• Early studies have
already found large
convection layers and
internal rotation rates.
• Global Oscillation
Network Group
(GONG) is a network
of world wide solar
oscillation
observatories.
Daily Grade 11 – Question 4
How are astronomers able to explore the layers of the sun
below the photosphere?
A. Short wavelength radar pulses penetrate the
photosphere and rebound from deeper layers within
the sun.
B. Long wavelength radar pulses penetrate the
photosphere and rebound from deeper layers within
the sun.
C. Highly reflective space probes have plunged below
the photosphere and sampled the sun's interior.
D. By measuring and modeling the modes of vibration
of the sun's surface.
The Solar Neutrino Problem
• The solar interior can not be
observed directly because it is highly
opaque to radiation.
• But neutrinos can penetrate huge
amounts of material without being
absorbed.
• Theory predicts that these particles
should be leaving the solar core and
radiating into space.
• A number of neutrino detector
experiments have been constructed
in an attempt to measure these
elusive particles.
• Early solar neutrino experiments
detected a much lower flux of
neutrinos than expected (the “solar
neutrino problem”).
Davis solar neutrino
experiment
Solar Neutrino Results
• Neutrinos come in three
“flavors”, but until recently
we could only detect electron
neutrinos.
• Recent results have proven
that neutrinos change
(“oscillate”) between
different types (“flavors”).
• Electron neutrinos are
produced in the high
numbers that the existing
model of solar activity
predicts, but about twothirds of them change
somewhere en route from the
Sun, morphing into some
combination of the two other
neutrino types, thus solving
the solar neutrino problem.
For Next Time
• Read Units 52, 54, 56, and 58.