1. Phys181Phys181Phys181Phys181 AstronomyAstronomyAstronomyAstronomy This Lecture Brought to You in Comic Sans MS

2. Quotes “With equal passion I have sought knowledge. I have wished to understand the hearts of [people]. I have wished to know why the stars shine.” -Bertrand Russell "One of the most impressive discoveries was the origin of the energy of the stars. One of the men who discovered this was out with his girl friend the night after he realized that nuclear reactions must be going on in the stars in order to make them shine. She said "Look at how pretty the stars shine!" He said, "Yes, and right now I am the only man in the world who knows why they shine." She merely laughed at him. Well, it is sad to be alone, but that is the way it is in this world.“ - Richard Feynman, "The Feynman Lectures“ “A star shines on the hour of our meeting.” - Elvish greeting, "The Lord of the Rings“ “I wonder why. I wonder why. I wonder why I wonder. I wonder why I wonder why I wonder.” - Richard Feynman

3. Readings: ASTRONOMY TODAY Chapter 16 (excepting section 16.6) Chapter 17 (without exception) ReadingsReadings

4. General Solar Properties Sol ar Pro pert ies

5. Why does the sun shine? Chemical Burning – insufficient radiation Radiative Cooling – only thousands of years Gravitational Contraction – only 25 million years Why does the sun shine?Why does the sun shine?

6. Stars convert energy into matter. E=mc^2E=mc^2

7. 600 million tons of H -> 598 million tons of He IN ONE SECOND Proton-Proton ChainProton-Proton Chain

8. Basic Solar Structure

9. The force of gravity inward and the radiation pressure outward balance each other out. Gravitational Equilibrium Radiation PressureRadiation Pressure

10. 91.2% Hydrogen – 8.7% Helium 0.1% Heavier Elements Spectroscopy Visible Spectrum Sp ect ros co py

11. LuminosityLuminosity Luminosity The total power output of the sun: 3.8x10 24 watts!!! Think of your 60 watt light bulb. 1 second of the earth luminosity contains enough energy to meet our needs for roughly 500,000 years! Only about one two-billionth of that reaches Earth.

12. Sun SpotsSun Spots Sun Spots Not at all dark Roughly the size of the earth Show the differences in rotation: 27 days equator – 31 days poles Only about one two-billionth of that reaches Earth.

13. GranularityGranularity Granularity of the Solar Surface

14. ConvectionConvection

15. A Solar Prominence ProminenceProminence

16. Solar Flare FlareFlare

17. Understanding the sun: simulationssimulations

18. End NEXT TIME: Measuring the Stars