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The Sun
Our Star
Please take your assigned transmitter
and swipe your student ID.
General Properties
• Average star
• Only appears so bright because it is so close.
• 109 times Earth’s diameter
• 333,000 times Earth’s mass
• Consists entirely of gas (av. density = 1.4 g/cm3)
• Central temperature = 15 million 0K
• Surface temperature = 5800 0K
Which parts of the sun can only be
seen during a total solar eclipse?
1.
2.
3.
4.
5.
Prominences
The solar corona
Sun spots
1 and 2
All of the above.
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Structure of the Sun
Apparent surface
of the sun
Heat Flow
Only visible
during solar
eclipses
Solar interior
Temp. incr.
inward
The Sun’s Interior Structure
Flow of energy
Photosphere
Energy transport
via convection
(explained soon)
Energy transport
via radiation
Energy generation
via nuclear fusion
Animation
Temp, density and pressure decr. outward
Do we have a direct view of the sun’s energy source?
1.
Yes, because the sun is just a
transparent gas ball.
Yes, because most of the energy
is produced very close to the
surface.
Yes, because the sun’s center is
so bright that the light is shining
through any material.
No, because the sun has a nontransparent solid surface.
No, because the radiation
produced in the center is
scattered around many times on
its way towards the surface.
2.
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5.
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How is energy produced in an H bomb?
1.
(Chemical) Burning of
hydrogen.
Nuclear fusion of hydrogen
into heavier elements.
Nuclear fission of hydrogen.
Nuclear fission of heavier
elements into hydrogen.
Nuclear fission of heavier
elements into elements
heavier than hydrogen.
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Energy generation in the Sun:
Fusion of Hydrogen into Helium
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.
Sun needs 1038 reactions,
transforming 5 million tons
of mass into energy every
second, to resist its own
gravity.
Need large proton speed ( high
temperature) to overcome
Coulomb barrier (electromagnetic
repulsion between protons).
T ≥ 107 0K =
10 million 0K
Energy Transport
Energy generated in the sun’s center must be transported to the surface.
Inner layers:
Radiative energy
transport
Outer layers (including
photosphere):
Convection
Cool gas
sinking down
g-rays
Gas particles
of solar
interior
Bubbles of hot
gas rising up
Granulation
… is the visible consequence of convection
Which every-day phenomenon is another
example of convective energy transport?
1.
Gas bubbles rising up in a
soda drink.
Gas bubbles rising up in
boiling water.
Giant waves moving onto
the sea shore.
Earthquakes.
All of the above.
2.
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5.
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Which every-day phenomenon is another
example of radiative energy transport?
1.
The heat of a bonfire
warming you when you’re
sitting close to it.
Heating food in the
microwave oven.
The air around a light bulb
heating up when the light is
on.
None of the above.
All of the above.
2.
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Very Important Warning:
Never look directly
at the sun through
a telescope or
binoculars!!!
This can cause permanent eye
damage – even blindness.
Use a projection technique or a
special sun viewing filter.
Sun Spots
Active Regions
Visible
Ultraviolet
Cooler regions of the photosphere (T ≈ 4240 K).
Considering that sunspots are cooler regions on the
photosphere with a temperature of ~ 4240 K, how would
you think a sunspot would appear if you could put it on the
night sky without the sun surrounding it?
1.
2.
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It would be invisible.
It would glow very faintly, similar to the
faint red glow of the eclipsed moon.
It would appear moderately bright,
comparable to the brightest stars.
It would appear very bright – even
brighter than the full moon.
It would be almost as bright as the sun
itself.
3.
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Solar Activity, seen in soft X-rays
What can we infer from the fact that we see the
gas above active regions (sun spots) mostly in
ultraviolet light and X-rays?
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5.
The gas must be very dense.
The gas must be very dilute.
The gas must be very hot.
The gas must be very cold.
The gas must consist mostly
of Helium.
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Sun Spots (III)
Magnetic North Poles
Magnetic
South Poles
Related to magnetic activity.
Magnetic field in sun spots is about 1000 times stronger
than average.
In sun spots, magnetic field lines emerge out of the photosphere.
Magnetic Field Lines
Magnetic
North Pole
Magnetic
South Pole
Magnetic
Field Lines
Mass ejection from the sun often follow magnetic field loops.
The Solar Cycle
Solar Maxima
Full 22-year cycle
11-year
cycle
Reversal of magnetic polarity (during solar minima)
After 11 years, the direction of
magnetic fields is reversed
=> Total solar cycle = 22 years
Are we currently near a solar
maximum or a solar minimum?
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1. Maximum.
2. Minimum.
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The Solar Corona
Very hot (T ≥ 1 million 0K), low-density gas
Prominences
Looped Prominences: gas ejected from the sun’s
photosphere, flowing along magnetic loops
Eruptive
Prominences
Extreme events, called
coronal mass ejections
(CMEs) and solar flares,
can significantly influence
Earth’s magnetic field
structure and cause
northern lights (aurora
borealis).
(Ultraviolet images)
Eruptive
Prominences
(Ultraviolet
images)