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Chp. 3, 11
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The Sun produces its energy from
a) Electric currents generated in its core
b) Chemical reactions (oxidation reactions)
producing flames
c) Fusion of hydrogen into helium
d) Disintegration of helium into hydrogen
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The Sun as a Star
(Chp. 11)
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About how many years elapse between times of
maximum solar activity?
a) 30
b) 11
c) 22
d) 1
e) None of the above.
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The Butterfly Diagram plots
a) Number of sunspots as a function of time
b) Number of sunspots as a function of
magnetic field strength
c) Rotation rate as a function of latitude
d) Sunspot position as a function of time.
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Solar Cycle
• The number of sunspots varies in an 11 year cycle
• Each sunspot peak is called a solar maximum
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Butterfly Diagram
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Maunder Minimum
1645-1715: extended lull in solar activity
“Little Ice Age” recorded in Europe
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The Sun-Earth Connection
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http://solar-center.stanford.edu/sun-on-earth/glob-warm.html
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Sun-Earth Connection
Geomagnetic: red
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Solar: blue
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Which of the following about the sunspot cycle is
not true?
a) The number of spots rises and falls every
11 years.
b) The pattern of the magnetic polarity of the
spots repeats every 22 years.
c) spots are located in regions of high
magnetic activity
d) spots are more readily seen near the
rotational poles of the Sun where magnetic field
lines are concentrated
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The Magnetic Field of the Sun
Current loop
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Differential Rotation plays important role in 11-year
cycle:
Rotation period at
equator: 25 days
Rotation period at
poles: 36 days
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What Powers the Sun?
1. Early Ideas
2. Modern Ideas
3. Fusion
4. How energy is transferred
• Conduction, Convection, Radiation
5. Hydrostatic Equilibrium
6. Lifetime of the Sun
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Early Ideas
• The Sun is a ball of fire.
Problem #1: A lump of coal the size of the Sun
would burn out in about 5000 years.
Problem #2: Temperatures involved are much too
high for common fire which is a chemical process
involving the electrons orbiting molecules.
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Early Ideas (cont)
• Gravity compresses interior of Sun to extreme
temperatures.
If you descend down a mine shaft, you’ll
notice that the temperature begins to
INCREASE with depth (below about 20 m
depth).
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Pressure and Temperature:
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Pressure and gravity:
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Early Ideas (cont)
• Gravity compresses interior of Sun to extreme
temperatures.
Problem #1: Sun is constantly losing energy.
To keep it shining with a steady brightness, it would
have to keep shrinking.
Problem #2: Whole process would take about
10 million years.
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Modern Ideas
1905: Einstein’s Theory of General Relativity
• Energy can be created from mass and vice-versa.
• All mass has an equivalent of amount of energy
which is given by the formula: E=mc2
For example: the mass in an aspirin is
equivalent to a small nuclear weapon.
How does the conversion take place?
- subatomic (nuclear) reactions
- process called fusion
- example: Proton-Proton Chain
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Review:
Isotopes
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Requires very high
temperatures
(greater
than 10 million K)!
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