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
The Sun’s Interior Structure
Temp, density and pressure decr. outward
Energy generation via nuclear fusion
Energy transport via radiation
Energy transport via convection
Flo
w o
f en
erg
y
Photosphere
Interior Structure of the SunMass composition
Mas
s fr
actio
n
r/R00.50.40.30.20.1 0.6
0.1
0.6
0.80.7
0.50.4
0.3
0.2
11H
42He
32He (x100)
The Sun’s Atmosphere
Only visible during solar eclipses
Apparent surface of the sun
Hea
t F
low
Solar interior
Temp. incr. inward
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
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
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
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
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.
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
Prominences
Looped Prominences: gas ejected from the sun’s photosphere, flowing along magnetic loops
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).
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)
The Chromosphere (II)
Spicules = filaments of
hot gas, visible in H
emission.
Streams extend up to ~ 10,000 km above photosphere
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