The Sun
Take-Away Points
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The Sun is an ordinary middle-sized star
The sun creates energy by nuclear fusion in its core
The visible surface of the Sun is called the photosphere
A thin cool layer, the chromosphere, allows us to determine
what the sun is made of
A very thin but very hot outer layer is called the corona
Convection in the sun is revealed by granulation
Features on the sun include sunspots, prominences, spicules
and faculae
Disturbances on the sun affect electrical and electronic
equipment on Earth
The Sun
• Distance: 150 million km (93 million miles) =
8.3 light minutes
• Diameter: 1.4 million km (870,000 miles) =
109 x Earth
• Mass = 330,000 x Earth
• Bulk density = 1.4 gm/cc
• Surface temperature = 5800 K
• Rotation: 25 days at equator, 34 at poles
1. The Sun is an ordinary middle-sized star
The Solar Interior
• Ideal Gas Law:
– Pressure x Volume is proportional to Temperature
• Pressure = weight of overlying material
2. The sun creates energy by nuclear fusion in its core
Interior of the Sun
% of Radius
Temperature K
Pressure (Atm)
Density (gm/cc) % of Mass
100
5700
.07
2 x 10-7
100%
90
600,000
2,130,000
0.026
99.8%
80
1,360,000
17,000,000
0.09
99%
70
2,300,000
66,000,000
0.2
97%
60
3,100,000
210,000,000
0.56
94%
50
4,000,000
720,000,000
1.3
89%
40
5,100,000
2.7 billion
3.9
79%
30
6,800,000
11 billion
12
61%
20
9,370,000
43 billion
35
33%
10
13,100,000
130 billion
87
7.7%
0
15,700,000
230 billion
154
0%
Structure of the Sun
• Core: 0-20% of radius. Energy produced by
nuclear fusion
• Radiative Zone: 20-70% of radius: Energy
travels as thermal radiation
• Tachocline: Boundary of Radiative Zone:
Exterior slips over interior
• Convective Zone: Outer 30% of Sun: Energy
moves by convection
2. The sun creates energy by nuclear fusion in its core
Core of the Sun
• Energy output: 90 billion megatons/second
• Energy output = 6 microwatts/kg – less than a candle
• Human body outputs 1.2 W/kg – 200,000 times
greater
• By volume: Core of Sun = 0.9 W/m3; Human body =
1200 W/m3.
• Trying to duplicate sun’s energy output not practical
on Earth; We try to use other fusion processes
• Energy takes 10,000 – 100,000 years to reach surface
2. The sun creates energy by nuclear fusion in its core
Solar Energy
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4 H  He
4H = 4 x 1.00794 = 4.03176
He = 4.002602
Difference = 0.029158 = 0.7% = 1/140
Converted to energy via E=mc2
Once you get over being freaked out by
Einstein, this is middle school math
2. The sun creates energy by nuclear fusion in its core
Solar Energy
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E=mc2
m = kg
c = m/sec = 300,000,000
E = joules (one Watt = 1 J/sec)
Sun’s energy output = 3.8 x 1026 W
How much mass is that per second?
m = E/c2 = 3.8 x 1026/(300,000,000)2 = 4
billion kg/sec
2. The sun creates energy by nuclear fusion in its core
Solar Energy
• Sun converts 4 billion kg of matter to energy
every second
• Matter conversion = 1/140 of original mass
• Sun converts 560 billion kg of H to He (5.6 x
1011 kg) every second
• Mass of Sun: 2 x 1030 kg
• 2 x 1030 kg/ 5.6 x 1011 kg/sec = 3.6 x 1018 sec =
114 billion years
2. The sun creates energy by nuclear fusion in its core
The Sun We Can See
• Photosphere: The Visible Disk
– More transparent than air
– We can see a couple of hundred kilometers deep
• Chromosphere
– Thin cooler atmosphere
– How we know what stars are made of
• Corona
– Very thin but very hot
– Why so hot is a mystery
Layers Of The Sun
Features On The Sun
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Limb Darkening
Granulation
Sunspots
Faculae
Plages: hot clouds in the Chromosphere
Flares
Prominences
Surface of the Sun
Supergranulation
Supergranulation
Sunspots
and
Faculae
Sunspots, Faculae, Limb Darkening
Solar Spicules
Solar Prominence
Solar Corona