1. Exploring the Active Sun PA STEM monthly meeting Lincoln HS, Philadelphia October 14, 2014

2. High-school standard HS-ESS1-1 focuses on the short-term evolution of the heliosphere PA STEM Science HS-ESS1-1: Develop a model based on evidence to illustrate the life span of the sun and the role of nuclear fusion in the sun’s core to release energy that eventually reaches Earth in the form of radiation. [Clarification Statement: Emphasis is on the energy transfer mechanisms that allow energy from nuclear fusion in the sun’s core to reach Earth. Examples of evidence for the model include observations of the masses and lifetimes of other stars, as well as the ways that the sun’s radiation varies due to sudden solar flares (“space weather”), the 11-year sunspot cycle, and non-cyclic variations over centuries.] [Assessment Boundary: Assessment does not include details of the atomic and sub-atomic processes involved with the sun’s nuclear fusion.]

3. Our sun has a life cycle and energy flow typical of low-mass stars Luminosity (“wattage”) of sun: L = 4 × 10 26 W Q: How do we know how much energy the sun puts out? Energy produced by nuclear fusion in core Q: How do we know that fusion is the sun’s energy source? PA STEM Science

4. Our sun has a life cycle and energy flow typical of low-mass stars Luminosity (“wattage”) of sun: L = 4 × 10 26 W Q: How do we know how much energy the sun puts out? Apparent brightness B measured at Earth’s surface Energy produced by nuclear fusion in core Q: How do we know that fusion is the sun’s energy source? PA STEM Science

5. Our sun has a life cycle and energy flow typical of low-mass stars Luminosity (“wattage”) of sun: L = 4 × 10 26 W Q: How do we know how much energy the sun puts out? Apparent brightness B measured at Earth’s surface Energy produced by nuclear fusion in core Q: How do we know that fusion is the sun’s energy source? Luminosity too high for other known processes Sun made of hydrogen (74%) and helium (25%) PA STEM Science

6. Nuclear fusion of hydrogen into helium creates excess energy and neutrinos Neutrinos Mass of 4 1 H: 4.0316 amu Mass of 4 He: 4.0026 amu Missing mass: 0.029 amu 0.73% of H mass turned into energy E = mc 2 PA STEM Science

7. Neutrinos allow us directly to observe the interior of the sun and the nuclear reactions occurring inside Neutrino picture of sun by Super-Kamiokande Locations of neutrino production in sun PA STEM Science Most energy is produced in the inner 11% of the sun’s radius

8. Rate of energy production allows the sun’s stable life span to be calculated PA STEM Science Mass of sun:2.0 × 10 30 kg Mass of H in sun: 1.5 × 10 30 kg(73.8%) Mass of H in fusing core: 2.0 × 10 29 kg(13%) Mass of H converted: 1.5 × 10 27 kg(0.73%) Energy of converted mass: 1.4 × 10 44 J(E = mc 2 ) Luminosity of sun: 4.0 × 10 26 J/s(1 W = 1 J/s) Q: How do we determine the sun’s expected life span?

9. Rate of energy production allows the sun’s stable life span to be calculated PA STEM Science Mass of sun:2.0 × 10 30 kg Mass of H in sun: 1.5 × 10 30 kg(73.8%) Mass of H in fusing core: 2.0 × 10 29 kg(13%) Mass of H converted: 1.5 × 10 27 kg(0.73%) Energy of converted mass: 1.4 × 10 44 J(E = mc 2 ) Luminosity of sun: 4.0 × 10 26 J/s(1 W = 1 J/s) Q: How do we determine the sun’s expected life span? Δt life = E converted /L sun = (1.4 × 10 44 J)/(4.0 × 10 26 J/s) = 3.5 × 10 17 s = 11 billion years (!)

10. Energy from the core heats the interior and is transported by convection to the surface PA STEM Science Temperature of core: 15 million K Temperature of surface: 5800 K

11. Heat from the surface (photosphere) is transported to the atmosphere (chromosphere) and corona PA STEM Science

12. Chromosphere and corona of sun are best viewed during solar eclipses PA STEM Science

13. Convection of heat to the photosphere forms granules, where the surface heats and cools PA STEM Science http://apod.nasa.gov/apod/ap111106.html

14. Sunspots are cooler regions of the photosphere that glow red but appear black against the bright sun PA STEM Science Temperature of surface: 5800 K Temperature of umbra: 4000 K

15. A current view of the sun’s photosphere is available from the SOHO spacecraft PA STEM Science Use your iPad to bring up the website http://sohowww.nascom.nasa.gov/

16. Monthly sunspot numbers vary in a regular cycle PA STEM Science Q: What is the average cycle time and how much does it vary?

17. Current sunspot cycle (#24) has been surprisingly weak PA STEM Science

18. Magnetism is the key to understanding the short- term activity in the sun PA STEM Science (See handout for discussion of magnetism)

19. Magnetic field lines chaotically burst through the sun’s surface PA STEM Science

20. Sunspots often come in magnetic pairs, with one a north pole and the other a south PA STEM Science Activity: Use your iPad to find the current SDO/HMI magnetogram on the SOHO site Photosphere (intensitygram)Photosphere (magnetogram) S N N N S S

21. Prominences are loops of hot, ionized gas above the photosphere formed by solar magnetic fields Hot gas following loops of magnetic field lines PA STEM Science

22. Solar flares, huge explosions above the photosphere, can release energy equal to a billion hydrogen bombs Solar flare PA STEM Science

23. Coronal mass ejections (CMEs) from solar flares or eruptive prominences can hit Earth and cause damage PA STEM Science http://www.cnn.com/video/data/2.0/video/world/2014/ 05/07/nr-vo-myers-solar-explosion.cnn.html http://www.cnn.com/2014/09/11/tech/innovation/sol ar-storm/index.html

24. Earth’s magnetic field traps these particles and directs them safely to the poles PA STEM Science

25. Collisions of diverted particles with the atmosphere give off the beautiful Northern lights PA STEM Science