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Solar Interior/
Nuclear Fusion
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Outline
• Solar interior• Fusion• Solar evolution• Stars
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Tutoring
• Wednesday 4:30-6:00• Berndt 640• USE IT OR LOSE IT
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Review
• Sunspots…• are darker because they are actually
cooler than the rest of the Sun• the result of a “kink” in the magnetic field• size of Earth; usually come in pairs• magnetic field switches every 11 year;
cycle is 22 years • Maunder minimum corresponded to mini
ice age
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Review
• and…• The solar equator rotates faster than the poles • the Zeeman effect is a splitting of spectral lines
from magnetic fields• sunspots magnetic field is about 1000x greater
than the surrounding area• solar wind is the sun evaporating
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As the Sun rotates, an individual sunspot can be tracked across its face.
From Eastern to Western limb, this takes about:A) 12 hours
B) A week
C) Two weeks
D) A month
E) 5.5 years
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As the Sun rotates, an individual sunspot can be tracked across its face.
From Eastern to Western limb, this takes about:A) 12 hours
B) A week
C) Two weeks
D) A month
E) 5.5 years
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Compared to the Earth, the Sun’s average density is:
A) lower
B) about the same
C) much greater
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Compared to the Earth, the Sun’s average density is:
A) lower
B) about the same
C) much greater
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From inside out, which is the correct order?
A) core, convective zone, radiative zone
B) photosphere, radiative zone, corona
C) radiative zone, convective zone, chromosphere
D) core, chromosphere, photosphere
E) convective zone, radiative zone, granulation
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Solar Atmosphere
• Photosphere - • What we see. (~5780 K)
• Chromosphere - • pinkish color (from H line); can see during eclipse.• cooler temperature (~4500 K)
• Transition zone/Corona -• Shift from absorption spectrum to emission spectrum• Corona very hot (~3 million K)
• Solar Wind -• The Sun is evaporating!
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Figure 9.10Solar Chromosphere
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Figure 9.12Solar Corona
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Figure 9.24Active Corona
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Figure 9.13Solar Atmospheric Temperature
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What about the internal structure?
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Solar Composition
Element
Number Percent
Mass Percent
H 91.2 71
He 8.7 27.1
O 0.078 0.97
C 0.043 0.4
N 0.0088 0.096
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Figure 9.2Solar Structure
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Internal Structure
• Core - • temperatures hot enough for nuclear reactions
(~15 million K)• Radiation Zone -
• Temperatures cooler, so no nuclear reactions.• Hot enough so everything is ionized. • Atoms can’t absorb photons.
• Convection Zone - • Temperature cooler. • Atoms form and can absorb radiation.
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Figure 9.6Solar Interior
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How do we know what is inside the Sun?
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How do we know what is inside the Sun?
Standard model
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Figure 9.4Stellar Balance
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Figure 9.5Solar Oscillations
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Figure 9.7Solar Convection
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Figure 9.8Solar Granulation
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Figure 9.11Solar Spicules
• dynamic jets• 5-10 minute life• possibly related
to seismic activity
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Typically, a granule in the photosphere of the sun is about the size of?
A) A city, ~20-30 kilometers across.
B) Texas, ~1000 km across.
C) The Earth, ~12,000 km across.
D) Jupiter, ~100,000 km across.
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Typically, a granule in the photosphere of the sun is about the size of?
A) A city, ~20-30 kilometers across.
B) Texas, ~1000 km across.
C) The Earth, ~12,000 km across.
D) Jupiter, ~100,000 km across.
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From inside out, which is the correct order?
A) core, convective zone, radiative zone
B) photosphere, radiative zone, corona
C) radiative zone, convective zone, chromosphere
D) core, chromosphere, photosphere
E) convective zone, radiative zone, granulation
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From inside out, which is the correct order?
A) core, convective zone, radiative zone
B) photosphere, radiative zone, corona
C) radiative zone, convective zone, chromosphere
D) core, chromosphere, photosphere
E) convective zone, radiative zone, granulation
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Misc notes
• Problem 9.1 • Should say “Section 9.1” and NOT 16.1.• And note that Mercury’s orbit is very
eccentric, so you can’t simply use the semi-major axis for it’s distance at perihelion.
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Nuclear Fusion
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Forces in Nature
• Gravity - long range; relatively weak.• Electromagnetic - long range; responsible
for atomic interactions (chemistry)• Weak Nuclear Force - short range;
responsible for some radioactive decay• Strong Force - short range; holds nuclei
together
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Nuclear Fusion
• Combining light nuclei into heavy ones.
nucleus 1 + nucleus 2 = nucleus 3 + energy
• Law of conservation of mass and energy
E = mc2
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Figure 9.25Proton Interactions
• Like charges (two protons) repel by electromagnetic force.
• With enough energy (temperature) and pressure, can overcome EM force
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Proton-Proton chain
• Most common reaction in the Sun.4 protons ==>> helium-4 + 2 neutrinos + energy
• Many other reactions are possible, but 90% are the proton-proton chain.
• Calculate energy produced from mass differences. (use E=mc2), get 4.3x10-12 J (Joules) when 4 protons fuse to Helium.
• From Sun’s luminosity, can calculate that 600 million tons of Hydrogen per second are fused into Helium.
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Figure 9.26Solar Fusion
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Proton-Proton chain
• Neutrinos - “little neutral one” are almost mass-less, and react with almost nothing.
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Figure 9.27Neutrino Telescope - Super Kamiokande
• Need large amounts of matter to detect neutrinos
• Solar Neutrino Problem - until recently could not explain observed low numbers.
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Proton-Proton chain
• Neutrinos “oscillations” explain the observation discrepancy.
• Neutrinos take eight minutes to get to the Earth from the Sun.
• In that time they can mutate (oscillate) into other forms.
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Three Minute Paper
• Write 1-3 sentences.• What was the most important thing
you learned today?• What questions do you still have
about today’s topics?