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Foundations of Astronomy | 13e
Seeds
Keep your voting card ready
Phys1411 – Introductory Astronomy
Instructor: Dr. Goderya
© Cengage Learning 2016
Exam 2
• A second chance to improve Exam 2 score
• Tuesday April 4th from 6-7:15 pm.
• Lab: Do it yourself activity to be assigned
on Tuesday.
Chapter 8
The Sun
Topics
I.
Introduction
A. Viewing the Sun
B. General Definition
C. General Properties
D. Chemical Composition
E. Basic Structure
II. The Solar Atmosphere
A. The Corona
B. The Chromosphere
C. Methods of Heat Transfer
D. The Photosphere
E. Temperature gradient in the Sun’s atmosphere
F. The Solar Wind
Outline (continued)
III. The Sunspot
IV. Helioseismology
V. Sunspot Activity
A. The Solar Cycle
B. Maunder Diagram
C. Solar Rotation
D. The Solar magnetic cycle
VI. Interior of the Sun
A. The Core and Envelope
B. Density and Pressure
C. Hydrostatic Equilibrium
VII. Nuclear Fusion in the Sun
A. Nuclear Binding Energy
B. Hydrogen Fusion
C. The Solar Neutrino Problem
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The Solar Interior - Helioseismology
The Solar Interior
How do we study the Sun’s interior?
• The Interior of the Sun is
opaque and can only be
studied with Helioseismology
• On Earth we measure
earthquakes with
seismographs
• Helioseismology is a technique
to measure the vibration
modes in the Sun
• The figure shows different
kinds of waves each with its
own wavelength and the
penetration depth.
• Using Doppler shifts as
the photosphere moves
gently up and down,
astronomers can map
the inside of the Sun
• This way we can
measure Density,
temperature, Pressure,
composition and
motion inside the Sun.
© Cengage Learning 2016
Solar Sunspot Activity
• Sunspots are
cooler regions
of the
Photosphere
(T ~ 4240K)
Solar Sunspot Cycles
The number of spots visible on the Sun varies in a cycle
with a period of 11 years. At maximum, there are often
more than 100 spots visible. At minimum, there are very
few or zero. Every 22 years the cycle repeats
• Still brighter
than the full
moon when
placed on the
night sky
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The Maunder Butterfly Diagram
Early in a cycle, spots appear at high latitudes north and
south of the Sun’s equator. Later in the cycle, new spots
appear closer to the Sun’s equator. If you plot the latitude of
sunspots versus time, the graph looks like butterfly wings,
as shown in this Maunder butterfly diagram, named after
E. Walter Maunder of Greenwich Observatory
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The Sun’s Magnetic Cycle – Differential Rotation
• (a) The photosphere of the Sun rotates faster at the equator than at
higher latitudes. Sunspot at different latitudes don’t move at the same
speed.
• (b) Detailed analysis of the Sun’s rotation from helioseismology
reveals that the interior of the Sun rotates differentially as well, with
regions of relatively slow rotation (blue) and rapid rotation (red).
Differential
rotation seems to
be responsible
for magnetic
cycle of the Sun
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Babcock Model
The Babcock model of the solar
magnetic cycle explains the
sunspot cycle as primarily a
consequence of the Sun’s
differential rotation gradually
winding up and tangling the
magnetic field near the base of the
Sun’s outer, convective layer.
Sunspots Tend to Occur in Groups or Pairs
• In sunspot groups, here
simplified into pairs of
major spots, the leading
spot and the trailing spot
have opposite magnetic
polarity.
• Spot pairs in the
Southern Hemisphere
have reversed polarity
from those in the
Northern Hemisphere.
© Cengage Learning 2016
Origins of Solar Wind
• Much of the solar wind
comes from coronal
holes where the
magnetic field does not
loop back into the Sun.
These open magnetic
fields allow ionized gas in
the corona to flow away
as the solar wind. The
dark area in the X-ray
image at right is a coronal
hole.
• X-Ray Images of the Sun
Reveal Coronal Holes
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Attendance
Solar Winds Interact with
the Earth magnetic field
and cause short term
climate changes.
© Cengage Learning
2016
ClassAction:
Astronomy
Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu)
Solar Interior: Core and Envelope
Core
Envelope
© Cengage Learning 2016
Campus.kellerisd.net
This where almost all the energy is generated
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Density Matters in the Sun
Sun Interior and Flow of Energy in the Sun
•
Near the center, nuclear
fusion reactions sustain high
temperatures.
•
Energy flows outward through
the radiative zone as photons
that gradually make their way
to the surface as they are
randomly deflected over and
over by collisions with
electrons.
•
In cooler, more opaque outer
layers the energy is carried by
rising convection currents of
hot gas (red arrows) and
sinking currents of cooler gas
(blue arrows
Density =Mass/Volume
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Density and Temperature in the Sun
Gravity Pulls Matter Inward
What Keeps the Sun from Collapsing on itself? KCVS
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Gas Pressure: Ideal Gas Law
Gas Pressure Pushes Outwards
Pressure = (density)(temperature)(constant)
• Gas Pressure is
the force of the
gas particles
colliding with the
walls of its
container
• Density and
Temperature
control the
amount of
pressure
Where Does Pressure Come From?
© Cengage Learning 2016
Indiana.edu
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Gravity and Sun
Hydrostatic Equilibrium
Energy in the Sun
Where does the Sun gets its energy from?
A State When Gravity Compression = Gas Pressure
Coal?
Chemical Burning?
Nuclear Fission?
Or
Nuclear Fusion?
Comparing The Sun with a Nuclear Bomb
• Total Output Power 4 x 1026 watts
– 100 billion 1 megaton nuclear bombs per second
– 4 trillion-trillion 100W light bulbs
Fission or Fusion
What kind of fuel can give such high temperatures and
Pressure?
World War II
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Comparing Oil, Coal and Fusion
• Nuclear Fusion is
more Efficient
© Cengage Astronomy
Learning 2016
ClassAction:
Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu)
© Cengage Learning 2016
Fusionforenergy.com
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Comparing fusion with burning
Converting 1 kg of Hydrogen into Helium
E = mc2 = (0.007kg) (3 x 108 m/s)2 = 6.3 x 1014 joule
20,000 metric tons of coal (2 x 107 kg) is needed to produce
this much energy
© Cengage Learning 2016
What Chemical Elements are Needed for
Nuclear Fusion or Fission?
What is Binding Energy?
Energy needed to disassemble the nucleus of an
atom.
Test your Learning
The Sun's luminosity comes primarily from
a) chemical burning.
b) the mechanical energy of turbulence.
c) nuclear fusion.
d) gravitational contraction.
e) all of the above are comparable in
importance.
© Cengage Learning 2016
http://hea-www.harvard.edu/~pgreen/educ/
Binding Energy Curve
• Obtained by
dividing the
binding energy
by the number
of nucleons in
the nucleus
• Fusion of Iron
subtracts
energy from
the core
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Conditions for Fusion to Occur
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Proton-Proton (P-P) reaction
http://astro.unl.edu/classaction/animations/sunsolarenergy/fusion01.html
• High Temperature (High Velocity)
• High Pressure
• High Density
In the Sun’s Core these conditions are met
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Converting Mass into Energy
4 H atoms = 6.693 x 10-27kg
-1 He atom = 6.645 x 10-27kg
_______________________
Mass Lost = 0.048 x 10-27kg
E = mc2
0.7% of mass converted to energy
E = mc2 = (0.048 x 10-27kg) (3 x 108 m/s)2 = 4.3 x 10-12 joule
Lights up a 10-watt bulb for a one-half of a trillionth of a second
107 times larger than burning in a chemical reaction
© Cengage Learning 2016
Test your Learning
© Cengage Astronomy
Learning 2016
ClassAction:
Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu)
Solar Neutrino Problem
What is a Neutrino?
The energy emitted by the Sun is produced
a) uniformly throughout the whole Sun.
b) throughout the whole Sun, but more in the
center than at the surface, as 1/r^2.
c) in a very small region at the very center of
the Sun.
d) from radioactive elements created in the Big
Bang.
© Cengage Learning 2016
http://hea-www.harvard.edu/~pgreen/educ/
It is a subatomic particle (Quarks and Leptons) with no charge.
Neutrino’s come in three flavors.
• The Sun produces 1012
neutrino’s that pass our bodies
every second
• So why can’ we detect them?
• Is there a problem in our
understanding of energy
mechanics in the Sun?
• Solar neutrino can oscillate in
these 3 flavors
© Cengage Learning 2016
Solar Neutrino Problem
• On Earth only electron neutrino
was detect the other two are not.
• But if neutrino can oscillate they
must have mass and hence
gravity.
• They could affect the evolution of
the Universe.
© Cengage Learning 2016
© Cengage Astronomy
Learning 2016
ClassAction:
Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu)
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The Solar Constant
• The Solar Constant Is the Amount of
Energy We Receive From the Sun
• The energy we receive from the sun is
essential for all life on Earth
• Solar Constant = F = 1360 J/m2/s
– F = Energy Flux =
Energy received in the form of radiation, per
unit time and per unit surface area [J/s/m2]
© Cengage Learning 2016
Acknowledgment
• The slides in this lecture is for Tarleton:
PHYS1411/PHYS1403 class use only
• Images and text material have been
borrowed from various sources with
appropriate citations in the slides,
including PowerPoint slides from
Seeds/Backman text that has been
adopted for class.
© Cengage Learning 2016
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