1. The Sun

2. How Old Is Our Sun?
Stars like the Sun shine for nine to ten billion years
The Sun is about 4.5 billion years old, judging by the age of moon rocks

3. The sun is a ball of glowing gas.
Like Earth, the sun has an interior and an atmosphere
Unlike Earth, the sun does not have a solid surface
Sun’s mass: ~ ¾ = Hydrogen (H), ¼ = Helium (He), with trace amounts of other elements

4. Cross Section of the Sun
Moving from the center out:
Core
Radiation zone
Convection zone
Photosphere
Chromosphere
Corona

6. The Sun’s Interior
Core
Radiation Zone
Convection Zone

7. Sun’s Interior: Core Innermost layer of interior
Sun produces energy in its core
Core reaches ~15 million ˚C
Energy through nuclear fusion: 2 H atoms form 1 He + heat and light (energy)
Heat and light move to sun’s atmosphere and into space

8. Sun’s Interior: Radiation Zone
Middle layer of interior
Region of tightly packed gas
Energy produced in core is transferred outward through radiation zone
Energy transferred in form of electromagnetic radiation
Can take ›100,000 years for energy to move through it

9. Sun’s Interior: Convection Zone
Outermost layer of interior
Hot gasses move through and cool at top of convection zone
Energy moves toward sun’s surface because loops of gas form as cooler gas sinks

10. The Sun’s Atmosphere
Photosphere
Chromosphere
Corona

11. The Sun’s Atmosphere: Photosphere
The inner layer of the sun’s atmosphere—the sun’s surface layer
Thick enough to be visible
Gives off visible light: photos is Greek for “light”
Layer from which the light we actually see (with the human eye) is emitted

12. The Sun’s Atmosphere: Chromosphere
Middle layer of sun’s atmosphere
Reddish glow that appears during total solar eclipse when moon blocks photosphere
Hotter than photosphere
Chroma is Greek for color

13. The Sun’s Atmosphere: Corona
Outermost layer of sun’s atmosphere
During total solar eclipse, looks like white halo
Extends for millions of km into space gradually thinning into solar wind
Corona is Latin for crown

14. Features on the Sun
Sunspots
Prominences
Solar Flares
Solar Wind

15. Sunspots
Areas of gasses on surface that are cooler than surrounding gasses
Don’t give off as much light—appear dark
Larger in size than the Earth
Energy sun produces changes slightly year to year (may be linked to number of sunspots)—may cause changes in Earth’s temperature

16. Prominences Huge, reddish loops of gas link different sunspot regions
If sunspots are near edge of sun as seen from Earth, appear to extend over edge of sun
Check out the Earth

17. Solar Flares Sometimes “loops” in sunspot areas connect
Rapid release of energy from these localized regions on the Sun in the form of electromagnetic radiation (magnetic energy)
The amount of energy released is the equivalent of millions of 100-megaton hydrogen bombs exploding at the same time!

18. Solar Wind
A stream of particles, primarily electrons and protons, flowing outward from the Sun at speeds as high as 900 km/s.
Essentially the hot solar corona expanding into space.

19. Solar Wind Reaches Earth
Particles enter our atmosphere at the poles
Create powerful electric currents causing gas molecules to glow
Can affect Earth’s magnetic field, causing magnetic storms
Disrupt communication and cause electrical power problems

20. Solar Center Stanford University
The sun rotates!
The sun rotates once every 27 days
Different parts of the sun rotate at different speeds
Solar Center Stanford University