1. Solar Nebula Theory and the Sun Don’t forget your sunblock!

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 Star: Celestial body of hot gasses (H and He) Star formation – A hot core surrounded by gas and dust 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. 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

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 H He Small atoms Large atom + Energy! 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 it balances with force of gravity pulling in matter toward core = stable star

15. Sun’s Nuclear Fusion

16. 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

19. 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

20. 2 Important processes: Convection and Radiation

21. Features of the Sun

22. 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

23. 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

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

25. 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