1. Part 6:The Sun Photo from http://sohowww.nascom.nasa.gov/bestofsoho/bestofsoho.htmlhttp://sohowww.nascom.nasa.gov/bestofsoho/bestofsoho.html

2. The Sun Is a star Made of gases Is our primary source of energy 70% hydrogen and 28% helium Light (radiation) Image at http://science.nasa.gov/headlines/y2007/images/chromosphere/LimbFlareJan12_strip2.jpg http://science.nasa.gov/headlines/y2007/images/chromosphere/LimbFlareJan12_strip2.jpg

3. How Big is the Sun? About 110 times wider than Earth Or 1.3 million times bigger than Earth Even a medium- sized sunspot is as big as the Earth! Photo from http://sohowww.nascom.nasa.gov/bestofsoho/bestofsoho.htmlhttp://sohowww.nascom.nasa.gov/bestofsoho/bestofsoho.html

4. How does our Sun compare to other Stars? Active stars range in size from supergiants to dwarfs Stars range from very bright (supergiants) to very dim (dwarfs) Stars range from very hot blue on the outside (O class) to cool red on the outside (M class) Our Sun is in-between--yellow Our Sun is a dwarf—medium mass Our Sun is a medium-bright dwarf

5. So is our Sun an average star? No—most stars are smaller and cooler than our Sun BUT Most of the bright stars we see are bigger and hotter

6. The Sun rotates at different speeds… At the equator, the Sun rotates once every 25.4 days Near its poles, the Sun rotates once every 36 days Known as “differential rotation” Click for movie

7. Sun’s Magnetic Field Winds up due to differential rotation Eventually forms loops and becomes tangled

8. Inside the Sun Core Radiative Zone Convection zone Image at http://solarscience.msfc.nasa.gov/interior.shtmlhttp://solarscience.msfc.nasa.gov/interior.shtml

9. The Sun’s Atmosphere Photosphere –Most of the sunlight we see is from here. The sun’s surface Chromosphere –Just above the photosphere –It is a thin layer that appears red in color Corona –The Sun’s atmosphere 1

10. Energy from the Sun Nuclear fusion reaction (hydrogen fusing forming helium) Releases radiation (gamma rays) The gamma ray loses energy as it bounces around inside the Sun It is finally released at the photosphere, primarily as visible light Image at http://solarscience.msfc.nasa.gov/interior.shtmlhttp://solarscience.msfc.nasa.gov/interior.shtml

11. Features in the Photosphere Sunspots –Dark and small (but brighter than Full Moon and big as Earth) –Cool-- temperatures only 6,200 F (Sun’s surface is 10,000 F) –Associated with magnetic fields: one set of spots is positive, other is negative Image at http://sohowww.nascom.nasa.gov/gallery/top10/top10_results.htmlhttp://sohowww.nascom.nasa.gov/gallery/top10/top10_results.html

12. More on Sunspots Our Sun has an activity cycle of 11 years Sunspots appear at specific latitudes on Sun –Bands of latitude move towards equator during cycle Images at http://starchild.gsfc.nasa.gov/docs/StarChild/questions/q uestion17.html and http://solarscience.msfc.nasa.gov/SunspotCycle.shtml http://starchild.gsfc.nasa.gov/docs/StarChild/questions/q uestion17.html http://solarscience.msfc.nasa.gov/SunspotCycle.shtml

13. Solar Events Flares (Explosions of energy on the surface of the Sun) Prominences: cloudlike gases looping above the sun Coronal Mass Ejections (massive clouds of plasma ejected from the Sun)

14. Solar Wind Blows charged particles and magnetic fields away from the Sun Charged particles captured by Earth’s magnetic field Create Auroras or Northern and Southern Lights Image at http://solarscience.msfc.nasa.gov/the_key.shtmlhttp://solarscience.msfc.nasa.gov/the_key.shtml

15. Auroras Electrons from solar wind are captured by the Earth’s magnetic field Interact with atoms in our atmosphere: oxygen and nitrogen make red and green; nitrogen can also make violet Northern lights are Aurora Borealis, while southern are Aurora Australis

16. Radiation Our Sun (and all active stars) emits radiation –Radio, infrared, visible, ultraviolet, x-ray and even some gamma rays –Most of the sunlight is yellow-green visible light or close to it The Sun at X-ray wavelengths Image and info at http://imagine.gsfc.nasa.gov/docs/teachers/gammaraybursts/imagine/page18.html and http://imagine.gsfc.nasa.gov/docs/teachers/gammaraybursts/imagine/page18.html http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/sun.html.

17. Sun’s Radiation at Earth The Earth’s atmosphere filters out some frequencies –Ozone layer protects us from some ultra-violet, and most x- rays and gamma rays –Water and oxygen absorb some radio waves –Water vapor, carbon dioxide, and ozone absorbs some infrared Electromagnetic spectrum http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/what_is_ir.html.

18. Young stars form in nebulae from Small Magellanic Cloud Image at http://hubblesite.org/newscenter/archive/releases/2007/04/image/a/results/50/ http://hubblesite.org/newscenter/archive/releases/2007/04/image/a/results/50/

19. Star-forming region in the Large Magellanic Cloud: http://hubblesite.org/newscenter/archive/releases/2008/31/image/a/results/50/ http://hubblesite.org/newscenter/archive/releases/2008/31/image/a/results/50/

20. Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/

21. Our Sun is a Regular/ Small Star Image at http://www.gsfc.nasa.gov/topstory/20011210insidesun.htmlhttp://www.gsfc.nasa.gov/topstory/20011210insidesun.html

22. By 5 billion years… White Dwarf Image at http://hubblesite.org/newscenter/archive/releases/nebula/planetary/1998/39/results/50/http://hubblesite.org/newscenter/archive/releases/nebula/planetary/1998/39/results/50/

23. Image at http://hubblesite.org/newscenter/archive/releases/nebula/planetary/2000/28/image/a/format/web_print/results/50/ http://hubblesite.org/newscenter/archive/releases/nebula/planetary/2000/28/image/a/format/web_print/results/50/

24. Image at http://hubblesite.org/newscenter/archive/releases/nebula/planetary/2004/27/image/a/format/large_web/results/50/http://hubblesite.org/newscenter/archive/releases/nebula/planetary/2004/27/image/a/format/large_web/results/50/

25. Massive Stars are different Image from http://hubblesite.org/newscenter/archive/releases/nebula/emission/1997/33/results/50/ http://hubblesite.org/newscenter/archive/releases/nebula/emission/1997/33/results/50/

26. Betelgeuse Image from http://hubblesite.org/newscenter/archive/releases/star/massive%20star/1996/04/image/a/results/50/http://hubblesite.org/newscenter/archive/releases/star/massive%20star/1996/04/image/a/results/50/

27. Supernova—Massive Star Explodes Images at http://hubblesite.org/newscenter/archive/releases/star/supernova/2004/09/results/50/ http://hubblesite.org/newscenter/archive/releases/nebula/supernova-remnant/2005/37/results/50/ http://chandra.harvard.edu/photo/2009/casa/