Download - General Properties
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General Properties
• Absolute visual magnitude MV = 4.83
• Central temperature = 15 million 0K
X = 0.73, Y = 0.25, Z = 0.02
• Initial abundances:
• Age: ~ 4.52 Gyr
• Spectral type G2V
• Effective (surface) temperature = 5770 0K
• Absolute bolometric magnitude Mbol = 4.76
The Sun
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The Sun’s Interior Structure
Temp, density and pressure decr. outward
Energy generation via nuclear fusion
Energy transport via radiation
Energy transport via convection
Flow
of e
nerg
yPhotosphere
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Interior Structure of the SunSite of main energy production
dL/d
r
r/R00.50.40.30.20.1
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Interior Structure of the SunMass composition
Mas
s fra
ctio
n
r/R00.50.40.30.20.1 0.6
0.1
0.6
0.80.7
0.50.40.30.2
11H
42He
32He (x100)
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The Sun’s Atmosphere
Only visible during solar eclipses
Apparent surface of the sun
Hea
t Flo
w
Solar interiorTemp. incr. inward
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Granulation
… is the visible consequence of convection
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Sun Spots (I)
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Sun Spots (II)
Visible Ultraviolet
Cooler regions of the photosphere (T ≈ 4000 K).
Active Regions
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Solar Activity, seen in soft X-rays
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Magnetic Fields in Sun Spots Magnetic fields on the photosphere can be
measured through the Zeeman effect
→ Sun Spots are related to magnetic activity on the photosphere
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Sun Spots (III)
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 North Poles
Magnetic South Poles
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Magnetic Loops
Magnetic field lines
Mass ejection from the sun often follow magnetic field loops.
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The Solar Cycle
11-year cycle
Reversal of magnetic polarity
After 11 years, North/South order of leading/trailing sun spots is reversed
=> Total solar cycle = 22 years
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The Sun’s Magnetic Cycle
After 11 years, the magnetic field pattern becomes so
complex that the field structure is re-arranged.
→ New magnetic field structure is similar to the
original one, but reversed!
→ New 11-year cycle starts with reversed magnetic-field
orientation
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The Solar Cycle (II)
Maunder Butterfly Diagram
Sun spot cycle starts out with spots at higher latitudes on the sun
Evolve to lower latitudes (towards the equator) throughout the cycle.
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The Maunder MinimumThe sun spot number also fluctuates on
much longer time scales:
Historical data indicate a very quiet phase of the sun, ~ 1650 – 1700: The Maunder Minimum
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Prominences
Looped Prominences: gas ejected from the sun’s photosphere, flowing along magnetic loops
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Eruptive Prominences
(Ultraviolet images)
Extreme events, called coronal mass ejections (CMEs) and solar flares,
can significantly influence Earth’s magnetic field structure and cause
northern lights (aurora borealis).
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Eruptive Prominences
(Ultraviolet images)
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Solar Aurora
Sound waves
produced by a solar
flare
~ 5
min
utes
Coronal mass ejections
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The Chromosphere
Chromospheric structures visible in H emission
Region of sun’s atmosphere just above
the photosphere.
T: 4400 K → 25,000 K
n: 1011 cm-3 → 107 cm-3
Absorption and emission lines from singly ionized metals (He
II, Fe II, Si II, Cr II, Ca II)
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The Chromosphere (II)
Spicules = filaments of
hot gas, visible in H
emission.
Streams extend up to ~ 10,000 km above photosphere
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The Transition Zone
h ~ 2300 – 2600 km above photosphere
Transition from moderate to high ionization
T ~ 25,000 → 106 K
n ~ 107 → 105 cm-3
Observe selective heights in (UV) emission lines of ionized metals
Ly → ~ 20,000 K
CIII 977 → ~ 90,000 K
O VI 1032 → ~ 300,000 K
Mg X 625 → ~ 1,400,000 K
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The Solar Corona
Very hot (T ≥ 106 K), low-density (n ≤ 105 cm-3) gas
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Active vs. Quiescent
Corona
Near Solar Maximum
Near Solar Minimum
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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.