Our Sun & Nuclear Fusion
(Chapter 7)
Student Learning Objectives
• Compare properties of the Earth and Sun
• Describe the layers of the Sun and how energy
is transported through each layer
• Analyze sunspots and solar activity.
What do we know about the Sun?
Surface Temperature
Mass
Diameter
Density
•
•
•
•
•
Sun
9,944 °F
1.988 x 1030 kg
1,392,000 km
1.5 g/cm3
Earth
57.2 °F
5.976 x 1024 kg
12,756 km
5.5 g/cm3
4 x 1026 Watts
100 times hotter than Earth’s hottest summer day
300,000 times more mass than Earth
109 Earth diameters
1,300,000 Earth volumes
Practice
The Sun is a low mass star. How does this
star compare and contrast with our Earth?
Energy Transfer
Energy is transported from hot to cold, through the
layers of a star, by two methods.
Radiation (light)
Convection (boiling)
What are the layers of the Sun?
 The Sun has 6 distinctive layers.
The Layers
1. Core: energy
production
2. Radiative Zone:
photons
4. Photosphere: photons
leave star
 “Surface” of the Sun.
Why?
 Limb Darkening
3. Convective Zone:
boiling fluid
 Granulation
o bubbles size of Texas
o last 10-20 minutes
5. Chromosphere: thin
jets of gas called spicules
 Transition Zone
 Temperature spikes
6. Corona: solar wind
 protons, electrons, & other
small particles
Corona
Density and temperature change in the layers.
Practice
1) Why does the corona escape the Sun?
2) How do astronomers know the layers of the
Sun? Hint: How do we know about the
interior of the Earth?
What mechanism is responsible for sunspots?
A sunspot is a relatively cooler
area on the surface of the Sun.
T = 4,240 Kelvin (8,155 ○F)
Change in size
Last days or months
Appear in pairs and groups
Image Credit: APOD
Sunspots form where energy is disrupted by magnetic
fields.
Differential rotations cause "kinks" in the magnetic
field lines.
Babcock
Model
Practice
1) A 60 Watt light bulb is 250 ○F. Would an
8,155 ○F sunspot be bright if it was isolated
from the surrounding photosphere?
2) Challenge: How would the energies compare
for the 60 Watt Light Bulb and a sunspot?
E = sT4
 Different levels in the Sun
rotate with different speeds
and the surface rotates at
different speeds.
The sunspot cycle peaks
every 11 years.
Full Cycle = 22 years
Equator = 25 days
Poles = 27.8 days
http://spaceweather.com/
Maunder Minimum
There is an unexplained absence of solar activity
recorded.
The Zeeman Effect shows strength of magnetic field.
Atom in magnetic field
Atomic energy levels are split into sublevels
Degree of splitting shows strength
What are the features that indicate solar activity?
All activity
observed on the
surface of the Sun,
and in the solar
atmosphere, is
caused by the
Sun’s magnetic
field.
Prominence
Filament
Flare
Practice
Does solar activity affect us on Earth?
(2014)
How do stars produce photons?
The definition of a star is
an object that has a core
density great enough to
sustain nuclear fusion.
Proton–Proton Chain
4 H  He + energy
1 Second in Our Sun
About 1038 reactions take place
600 billion kg of hydrogen is
converted into helium
4 billion kg of mass becomes energy
Practice
Our star will last another 5-6 billion years. How is
this possible with so much mass loss each second?