The Sun

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. The sun rotates! • The sun rotates once every 27 days • Different parts of the sun rotate at different speeds Solar Center Stanford University http://science.nasa.gov/ssl/pad/solar/sunturn.htm