1. Our Sun & Nuclear Fusion
(Power Point 13)
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.
Image Credit: APOD

3. https://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=188
Image Credit: NASA

4. 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

5. 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

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

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

8. The Layers Core: energy production
Radiative Zone: photons travel from core through this layer
Convective Zone: boiling fluid transfers energy
Photosphere: photons leave star
Surface of the Sun
Limb Darkening
Granulation
bubbles size of Texas
last minutes

9. Recorded at Big Bear Solar Observatory
Recorded at Big Bear Solar Observatory

10. Chromosphere: thin jets of gas called spicules Corona: solar wind
Transition Zone
Temperature spikes
Corona: solar wind
protons, electrons, and other small particles leave the Sun

11. Corona Image Credit: APOD
Corona
Image Credit: APOD

12. Practice In which layer of the Sun is energy produced?
Describe a spicule.
List the layers of the Sun.

13. 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

14. Practice Why does the corona 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?

15. 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: NASA

16.
Image Credit: APOD

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

18. 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
S-N back to N-S

19. Image Credit: NASA

20. Practice
A 60 Watt light bulb is 250 ○F. Would an 8,155 ○F sunspot be bright if it was isolated from the surrounding photosphere?
How would the energies compare for the 60 Watt Light Bulb and a sunspot? Hint: Energy depends on T4

21. The Zeeman Effect shows strength of magnetic field.
Atomic energy levels are split into sublevels
Degree of splitting  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.
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
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?