1. Ch9 THE SUN AND STARS The star we see by day

2. Ch9 The Sun, Our Star The Sun is an average star. From the Sun, we base our understanding of all stars in the Universe. No solid surface.

3. Ch9 Vital Statistics Radius = 100 x Earth (696,000 km) Mass = 300,000 x Earth (1.99 x 10 30 kg) Surface temp = 5,800 K Core temp = 15,000,000 K Luminosity = 4 x 10 26 Watts Solar “Day” = –24.9 Earth days (equator) –29.8 Earth days (poles)

4. Ch9 In The Core Density = 20 x density of Iron Temperature = 15,000,000 K Hydrogen atoms fuse together. Create Helium atoms.

5. Ch9 Nuclear Fusion 4H  He The mass of 4 H nuclei (4 protons): 4 x (1.6726 x10 -27 kg) = 6.690 x 10 -27 kg The mass of He nuclei: = 6.643 x 10 -27 kg Where does the extra 4.7 x 10 -29 kg go? ENERGY!  E = mc  E = (4.7 x 10 -29 kg ) x (3.0 x 10 8 m/s) 2 E = hc/  = 4.6 x 10 -14 m (gamma rays) So: 4H  He + light!

6. Ch9 Solar Cross-Section Progressively smaller convection cells carry the energy towards surface. See tops of these cells as granules.

7. Ch9 H  Sun Photo by Big Bear Solar Observatory

8. Ch9 Prominences

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10. Ch9 Aurorae The solar wind passes out through the Solar System. Consists of electrons, protons and other charged particles stripped from the Sun’s surface. When charged particles and magnetic fields interact: light!

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12. Ch9 Solar Cycle Increase in solar wind activity - Coronal Mass Ejections Increase in Auroral displays on Earth Increase in disruptions on and around Earth. Courtesy of SOHO/LASCO/EIT consortium.

13. Ch9 Magnetic fields and Sunspots At kinks, disruption in convection cells. Sunspots form.

14. Ch9 Sunspots 11-year sunspot cycle. Center – Umbra: 4500 K Edge – Penumbra: 5500 K Photosphere: 5800 K

15. Ch9 Magnetic fields and Sunspots Where magnetic fields “pop out” of Sun, form sunspots. Sunspots come in pairs.

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19. Ch9 Stars

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21. Ch9 Spectral Classifications

22. Ch9 Supergiants, Giants, and Dwarfs

23. Ch9 Stellar Radii How big are stars? We see stars have different luminosities and different temperatures. Stars have different sizes. If you know: –Distance –Angular size Learn real size. 50 mas