1. Our Sun & Nuclear Fusion
(Power Point 11)
Image Credit: NASA

2. Student Learning Objectives
Construct a model of the solar system
Describe the layers of the Sun and how energy is transported through each layer
Explain sunspots and solar activity
Video Credit: APOD

3. What do we know about the Sun?
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
Sun
Earth
Surface Temperature
9,944 °F
57.2 °F
Mass
1.988 x 1030 kg
5.976 x 1024 kg
Diameter
1,392,000 km
12,756 km
Density
1.5 g/cm3
5.5 g/cm3

4. Energy Transfer
Energy is transported from hot to cold, through the layers of a star, by two methods.
Radiation (light)
Convection (boiling)
Image Credit: Creative Commons

5. Practice Does the Earth emit electromagnetic radiation?
Is the Sun a relatively hot or cool star?
Can convection occur in air? Explain.

6. What are the layers of the Sun?
Image Credit: NASA

7. Bubbles the size of Texas
The Layers
Core: energy production takes place here
Radiative Zone: photons leave the core and travel through this layer, transferring energy by radiation
Convective Zone: boiling fluid transfers energy in this layer
Photosphere: photons leave star
Surface of the Sun
Limb Darkening at edges
Granulation on surface
Bubbles the size of Texas
last minutes

8. Recorded at Big Bear Solar Observatory
Recorded at Big Bear Solar Observatory

9. Chromosphere: this layer is comprised of thin gas jets called spicules
Transition Zone
Temperature spikes
Corona: constantly changing solar wind
Comprised of small particles (p, e−, etc.)
Mass leaves the Sun

10. Corona Image Credit: APOD
Corona
Image Credit: APOD

11. Practice In which layer of the Sun is energy produced?
Describe a spicule.
List the layers of the Sun, and state the type of energy transfer that occurs in that layer.

12. Density & Temperature (Core  Outward)
Density decrease rapidly from core through corona.
Temperature decreases rapidly from core through photosphere.
Temperature spikes up in the chromosphere.
Image Credit: University of Northern Iowa

13. Practice Explain why the corona is able to escape the Sun.
How do astronomers know the layers of the Sun? Hint: How do we know about the interior of the Earth?
Why is the photosphere called the surface?
Which layer(s) is/are the atmosphere of the Sun?

14. 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)  
Spots change in size
Sets of spots will last days or months
Spots always appear in pairs
Image Credit: NASA

15.
Image Credit: APOD

16. Sunspots form where energy is disrupted by the magnetic field.
Differential rotations cause the magnetic field to become “tangled” resulting in "kinks" in the magnetic field lines.
Babcock
Model

17. Differential Rotation & Sunspot Cycle
Different layers in the Sun rotate with different speeds.
Different latitudes on the surface rotate at different speeds.
Equator = 25 days
Poles = 27.8 days
The sunspot cycle peaks every 11 years
Full Cycle = 22 years
N-S to S-N to N-S

18. Solar Cycles
Image Credit: NASA

19. Practice
A 60 Watt light bulb is 250 ○F. Explain why an 8,155 ○F sunspot appears to be dark.
How would the energies compare for the 60 Watt Light Bulb and a sunspot? E = sT4

20. Solar Activity
The Zeeman Effect shows is used to determine the strength of a magnetic field.
Atomic energy levels are split into sublevels
Degree of splitting indicates strength of field
All activity observed on the surface of the Sun, and in the solar atmosphere, is caused by the Sun’s magnetic field.

21. Zeeman Effect
Image Credit: NASA

22. What are the features that indicate solar activity?
Prominence
Image Credit: APOD

23. Filament
Flare
Image & Video Credit: NASA & Spaceweather.com

24. Practice
Differentiate between a solar prominence and a solar filament.
How are prominences and filaments different from flares?
Can solar activity affect us on Earth?

25. 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

26. 1 Second in Our Sun
1038 reactions 600 billion kg Hydrogen converted into Helium 4 billion kg of mass becomes energy
Image Credit: NASA

27. Practice Name the two ways our star, the Sun is losing mass.
Our star will last another 5-6 billion years. How is this possible with so much mass loss each second?
What are the contributing factors for how long a star will live?