1. Announcements Pick up graded homework Seminar on gravitational waves today, 1:00, SL 240 No class this Friday! Test next week on material through today’s class

2. Our Sun 18 October 2006

3. Today: Basic facts about the sun Solar details: Granulation, sunspots, magnetic fields, flares, prominences, corona, solar wind What is the sun made of?

4. Basic facts about the Sun Distance from earth: 150 million km (400 x as far as moon) Angular diameter: 1/2 degree (same as moon) True diameter: 110 x earth’s diameter Mass: 330,000 times earth’s mass Average density: 1.4 times that of water Intensity of sunlight at earth’s location: 1400 watts per square meter Total power output: 3.9 x 10 26 watts Surface temperature: 5800 K Made of ionized gases

5. Basic facts about the Sun Distance from earth: 150 million km (400 x as far as moon) measured using radar Angular diameter: 1/2 degree (same as moon) True diameter: 110 x earth’s diameter (400 x moon’s) Mass: 330,000 times earth’s mass gravity! Average density: 1.4 times that of water mass/volume Intensity of sunlight at earth’s location: 1400 watts per square meter measure directly Total power output: 3.9 x 10 26 watts calculate Surface temperature: 5800 K from power or spectrum Made of ionized gases too hot for anything else!

6. Sunspots, Granulation For current images and sun news, see www.spaceweather.com

7. Electromagnetism The sun is made of ionized atoms and electrons -- electrically charged particles Charged particles in motion create magnetic fields Magnetic fields can “trap” electrically charged particles (which can move parallel to the field but can’t go far in perpendicular directions)

8. Magnetic activity around sunspots Visible lightMagnetic field mapFar-ultraviolet light

9. Magnetic activity around sunspots (Ultraviolet light images)

10. Solar Prominences

12. The Solar Corona

13. The Solar Corona and Solar Wind

14. Solar Wind and Earth’s Magnetic Field Charged particles (mostly from the sun) are deflected by earth’s magnetic field; some are trapped and move back and forth along helical paths. They reach earth’s atmosphere mostly in the polar regions.

15. Aurora (Northern/Southern Lights) From Earth From the Space Shuttle

16. What is the sun made out of? 74% hydrogen (by mass) 25% helium 1% all other elements (oxygen, carbon, nitrogen, neon, aluminum, silicon, iron,... )

17. The Periodic Table Masses and rarities increase (mostly) toward the bottom of the table.