THE SUN 1 million km wide ball of H, He undergoing nuclear
fusion. Contains 99% of the mass in the whole solar system! Would
hold 1.3 million earths! 386 billion billion megawatts of power
produced. 15 minutes of this is equivalent to all the energy
consumed by humans in 1 year. 4 million tons of H are consumed
every second, but there is enough to burn for another 5 billion
years!
Slide 3
THE SUN 150M km (93M miles; 8 light-minutes; 1 AU) from Earth 1
R s = 700,000 km = 100 R e 1 M s = 2 x 10 30 kg = 300,000 M e Mean
density = 1.4 g/cm 3 Energy flux at Earth (solar constant) = 1400
W/m 2 4 x 10 26 W luminosity Rotation: differential, 25 days at
equator, 35 days at poles Figure: near-perfect sphere; < 10 km
of oblateness Surface gravitational acceleration: 274 m/s 2 Surface
temperature about 5800 K Core temperature about 13.6 million K Core
pressure about 150 billion atmospheres Core density 150 x water
(150,000 kg/m 3 )
Slide 4
Slide 5
Slide 6
Slide 7
P-p chain fusion
Slide 8
1 He weighs slightly less than 4 H
Slide 9
For how long will the Sun burn? Sun will stay in current
evolutionary track until 10% of H is consumed. H burning is 0.7%
efficient e.g. mass to energy conversion due to mass difference
between H and He Sun burns at rate of 3.846 x 10 26 J/s
Slide 10
How does this compare to other sources? Combustion: 1 kg of
coal per square meter per second will last 10,000 years
Gravitational contraction (Kelvin-Helmholtz): Falling objects
convert gravitational energy to heat Matter falls into the Sun due
to contraction Contraction by 20 m per year. will last 100 million
years
Slide 11
Hydrostatic Equilibrium
Slide 12
Slide 13
Slide 14
Wiens Displacement Law
Slide 15
Slide 16
Slide 17
Slide 18
Slide 19
Slide 20
Slide 21
Slide 22
Slide 23
Slide 24
Core: totally ionized; fusion reactions occur; 15M K Radiation
zone: ionized, dense and variably transparent (opaque over short
distances) to radiation; random walk of photons and continual
absorption and re-radiation takes 10 4 to10 6 years to traverse; 7M
K Convective zone: energy more efficiently transported via
convection cells; 2M K
Slide 25
Slide 26
Slide 27
Spherical Harmonic Normal Modes
Slide 28
Helioseismology
Slide 29
Rotational speeds within the Sun. Red = fastest Blue = slowest
Inner 70% rotates at uniform rate Outer 30% has differential
rotation due to convection zone
Slide 30
Slide 31
Slide 32
Photosphere: bubbling surface of the sun where most of visible
light comes from; has 1000 km scale granularity (top of convection
cells) that exist for 15-20 minute timescales; 5800 K Chromosphere:
thin (2000 km) cool (4500 K) skin over photosphere; pink color due
to H Transition zone: rapid rise in temperature Corona: vast,
extremely hot and ionized cloud around sun; 1M K
Slide 33
Slide 34
Slide 35
Slide 36
Slide 37
Slide 38
chromosphere
Slide 39
UV He ion emission Upper part of chromosphere at 60000 K
Prominence 60-80000 K Corona 1M K
Slide 40
Corona Highly ionized zone (1M-3M K) Why so hot??!!
Slide 41
Extends to 706,000 km +
Slide 42
Corona in the extreme UV Coronal loops Coronal holes
Slide 43
extreme UV Fe ion (14+) emission Dark = coronal hole (magnetic
field opens out to space and source of high- velocity solar
wind)
Slide 44
soft X-ray Bright = hot spots in corona Dark at top = coronal
hole
Slide 45
Radio Acquired near solar maximu m
Slide 46
Slide 47
Slightly cooler areas on the photosphere (4500 K) 10,000 km
wide Several day to month lifetimes Locations of twisted and
compressed magnetic field lines Migration can be used to track
differential rotation of Sun 11 year cycle; number of sunspots
related to amount of solar activity
Slide 48
Slide 49
Slide 50
Slide 51
Slide 52
Slide 53
Slide 54
We are currently at an unusually quiet and long- lived
minimum
Slide 55
magnetogram
Slide 56
UV image
Slide 57
Slide 58
Slide 59
Slide 60
Slide 61
Slide 62
Slide 63
Slide 64
Slide 65
Slide 66
Slide 67
Slide 68
Slide 69
Magnetic field polarity flips during 11-year sunspot cycle
Complete cycle from N to S to N takes 22 years
Slide 70
Slide 71
Slide 72
Slide 73
Solar Wind Supersonic flow of material from photosphere and
corona. Has sufficient kinetic energy to achieve escape velocity
400 km/sec + Extends outward for 10M km
Slide 74
Slide 75
Slide 76
Slide 77
Slide 78
Prominences: 100,000 km scale ejections of mass Usually closed
loops around magnetic field lines Relatively cool clouds of H
gas
Slide 79
Slide 80
Slide 81
Slide 82
X-rays Bright area is active region in corona (coronal
condensation ) associated with a flare and sunspot group
Slide 83
Solar Flares Short-lived, sudden increases in brightness (and
associated jets of material and release of large amount of energy)
near sunspots Bursts of electromagnetic energy as magnetic field
lines snap
Slide 84
Slide 85
Coronal Mass Ejection
Slide 86
Slide 87
Very damaging space weather phenomenon associated with magnetic
storms in the Earths ionosphere Can disable spacecraft and ground
electrical and telecommunic ation systems
