Exploring the Sun: Our Local Star

1. Exploring the Sun: Our Local Star Don’t forget your sunblock! (2.2)

2. The Sun • Most important celestial object for life on Earth • Contributes heat  moderate temperatures • Contributes light  visibility • Photosynthesis  provides autotrophs with energy to make food,  provides consumers with food

3. Where Did it Come From? • Current theory: Solar Nebula Theory • Stars and planets formed together • A Star is a celestial body of hot gasses (H and He) • When a star forms, its hot core remains surrounded by gas and dust that hasn’t been pulled into the center • Gas and dust = nebula • Sometimes, this leftover material drifts into space • Sometimes, it remains in the nebula, bound by gravity

4. How the Solar System Formed

5. How the Solar System Formed • Gravity sets gas and dust particles into motion • No resistance in space! • The closer the particles get to each other, the stronger the force of gravity • Particles aren’t perfectly aligned so they end up spinning around in a nebula

6. How the Solar System Formed • Spinning nebula contracts and flattens into a disc • Accretion disc • Particles begin to gather in the centre of the nebula • Forming a protostar (hot, condensed object)

7. How the Solar System Formed • Tiny grains or small lumps collect in nebula  attract others and build up to bigger, rocky lumps called planetismals • If planetismals survive collisions, they may build up to full planets like those in our solar system • If their mass is >10x that of Jupiter, fusion begins and a star is formed

8. How the Solar System Formed

9. How the Solar System Formed

10. How the Solar System Formed

11. Extrasolar planets • Many planets have been discovered in orbit about stars other than the Sun • “extrasolar planets” • They can be detected by • A) the dimming of their star’s light as they pass in front of it • B) direct photos

12. How the Sun Formed • Nebula collapses, contracts, and gas compresses • Friction of all that material in nebula causes a temperature increase • At 10 000 000°C, nuclear fusion begins • The combining of 2 atomic nuclei to form 1 large nucleus • H + H  He + energy

13. Sun’s Nuclear Fusion H He + Energy! Small atoms H Large atom • 1 g of Hydrogen provides enough energy for a home in Canada for about 40 years

14. Sun’s Nuclear Fusion • H nuclei combine to form Helium • Requires massive pressure and temp • Now called “protostar” • He is more dense that H • :. He settles in Sun’s core • Pressure in the core is very high. When is balances with force of gravity pulling in matter toward core = stable star

15. Sun’s Nuclear Fusion

16. Sun’s Nuclear Fusion • When the sun converts ~ 10% of H to He, He core accumulates and undergoes fusion itself • Sun changes physically • He core grows • H fusion (ring around core) also grows • :. The sun is growing… yowsa! • ~ 30% larger than its protostar phase

17. Sun’s Nuclear Fusion

18. Structure of the Sun • He core (where solar energy is produced) • Radiative zone: 86% of sun’s energy radiates outward from core • Convective zone: outer layer transfers energy in convection currents back in towards sun • Photosphere: “surface” layer of sun

19. 2 Important processes: Convection and Radiation

20. Features of the Sun

21. Sunspots • Def: An area of strong magnetic force on the photosphere • Sunspots are not dark, they are bright • Appear dark due to contrasting temperature to photosphere • Photosphere: 6000˚C • Sunspot: 4500˚C

22. Sunspots • By observing sunspots, astronomers learned the sun rotates in 27-35 days • Gradually grow, may fade and disappear altogether • Occur in 22-year cycles

23. Solar Flare Solar flare: Magnetic fields explosively eject intense streams (solar wind) of charged particles into space

24. Solar Flare • If one of the streams hits Earth, it can: • Disrupt telecommunication and electrical equipment • Usually beautiful auroras • Shimmery curtains of high energy, charged particles • Electric currents charging gasses in Earth’s atmosphere