Properties of Sun

1. Properties of Sun www.assignmentpoint.com

2. Goals • Summarize the overall properties of the Sun. • What are the different parts of the Sun and how do we know this? • Where does the light we see come from? • Solar activity and magnetic fields. www.assignmentpoint.com

3. The Sun, Our Star • The Sun is an average star. • From the Sun, we base our understanding of all stars in the Universe. • Like Jovian Planets it’s a giant ball of gas. • No solid surface. www.assignmentpoint.com

4. Vital Statistics • Radius = 100 x Earth (696,000 km) • Mass = 300,000 x Earth (1.99 x 1030 kg) • Surface temp = 5780 K • Core temp = 15,000,000 K • Luminosity = 4 x 1026 Watts • Solar “Day” = • 24.9 Earth days (equator) • 29.8 Earth days (poles) www.assignmentpoint.com

5. Structure • ‘Surface’ • Photosphere • ‘Atmosphere’ • Chromosphere • Transistion zone • Corona • Solar wind • ‘Interior’ • Convection zone • Radiation zone • Core www.assignmentpoint.com

6. The Solar Interior • How do we know what’s inside the Sun? • Observe the outside. • Theorize what happens on the inside. • Complex computer programs model the theory. • Model predicts what will happen on the outside. • Compare model prediction with observations of the outside. • Scientific Method! www.assignmentpoint.c om

7. Helioseismology • Continuous monitoring of Sun. • Ground based observatories • One spacecraft (SOHO) • Surface of the Sun is ‘ringing’ • Sound waves cross the the solar interior and reflect off of the surface (photosphere). www.assignmentpoint.com

8. Interior Properties • Core = 20 x density of iron • Surface = 10,000 x less dense than air • Average density = Jupiter • Core = 15,000,000 K • Surface = 5780 K www.assignmentpoint.com

9. Do you see the light? • Everything in the solar system reflects light. • Everything also absorbs light and heats up producing blackbody radiation. • Q: Where does this light come from? • A: The Sun. • But where does the Sun’s light come from? www.assignmentpoint.com

10. Our Journey through the Sun • Journey from the Sun’s core to the edge of its ‘atmosphere.’ • See where its light originates. • See what the different regions of the Sun are like. • See how energy in the core makes it to the light we see on Earth. www.assignmentpoint.com

11. Density = 20 x density of Iron Temperature = 15,000,000 K Hydrogen atoms fuse together Create Helium atoms. In The Core www.assignmentpoint.com

12. Nuclear Fusion • 4H  He • The mass of 4 H atoms: 4 x (1.674 x10-27 kg) = 6.694 x 10-27 kg • The mass of He atom: = 6.646 x 10-27 kg • Where does the extra 4.8 x 10-29 kg go? • ENERGY!  E = mc2 • E = (4.8 x 10-29 kg ) x (3.0 x 108 m/s)2 • E = hc/l l = 4.6 x 10-14 m (gamma rays) • So: 4H  He + light! www.assignmentpoint.com

13. The Radiation Zone • This region is transparent to light. • Why? • At the temperatures near the core all atoms are ionized. • Electrons float freely from nuclei • If light wave hits atom, no electron to absorb it. • So: Light and atoms don’t interact. • Energy is passed from core, through this region, and towards surface by radiation. www.assignmentpoint.com

14. The Convection Zone • This region is totally opaque to light. • Why? • Closer to surface, the temperature is cooler. • Atoms are no longer ionized. • Electrons around nuclei can absorb light from below. • No light from core ever reaches the surface! • But where does the energy in the light go? • Energy instead makes it to the surface by convection. www.assignmentpoint.com

15. Convection • A pot of boiling water: • Hot material rises. • Cooler material sinks. • The energy from the pot’s hot bottom is physically carried by the convection cells in the water to the surface. • Same for the Sun. www.assignmentpoint.com

16. Solar Cross-Section • Progressively smaller convection cells carry the energy towards surface. • See tops of these cells as granules. www.assignmentpoint.com

17. The Photosphere • This is the origin of the 5800 K blackbody radiation we see. • Why? • At the photosphere, the density is so low that the gas is again transparent to light. • The hot convection cell tops radiate energy as a function of their temperature (5800 K). l = k/T = k/(5800 K)  l = 480 nm (visible light) • This is the light we see. • That’s why we see this as the surface. www.assignmentpoint.com

18. The Solar Atmosphere • Above the photosphere, transparent to light. • Unlike radiative zone, here atoms not totally ionized. • Therefore, there are electrons in atoms able to absorb light. • Absorption lines in solar spectrum are from these layers in the atmosphere. www.assignmentpoint.com

19. Atmospheric Composition • Probably same as interior. • Same as seen on Jupiter. • Same as the rest of the Universe. www.assignmentpoint.com

20. The Chromosphere • Very low density • But also very hot • Same as the gas tubes we saw in class and lab. • Energy from below excites the atoms and produces emission from this layer. • Predominant element – Hydrogen. • Brightest hydrogen line – Ha. • Chromosphere = color www.assignmentpoint.com

21. Spicules and Prominences • Emission from the atmosphere is very faint relative to photosphere. • Violent storms in the Chromosphere. • Giant curved prominances • Long thin spicules. www.assignmentpoint.com

22. Prominences www.assignmentpoint.com

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24. Ha Sun www.assignmentpoint.com Photo by Robert Gendler

25. Corona • Spicules and other magnetic activity carry energy up to the Transition Zone. • 10,000 km above photosphere. • Temperature climbs to 1,000,000 K • Remember photosphere is only 5800 K • The hot, low density, gas at this altitude emits the radiation we see as the Corona. www.assignmentpoint.com

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27. The X-Ray Sun • Q: At 1,000,000 K where does a blackbody spectrum have its peak? • A: X-rays • Can monitor the Solar Coronasphere in the X-ray spectrum. • Monitor Coronal Holes www.assignmentpoint.com

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29. Solar Wind • At and above the corona: • Gas is very hot • Very energetic • Like steam above our boiling pot of water, the gas ‘evaporates’. • Wind passes out through Coronal Holes • Solar Wind carries away a million tons of Sun’s mass each second! • Only 0.1% of total Sun’s mass in last 4.6 billion years. www.assignmentpoint.com

30. The Aurora • The solar wind passes out through the Solar System. • Consists of electrons, protons and other charged particles stripped from the Sun’s surface. • Interaction with planetary magnetic fields gives rise to the aurora. www.assignmentpoint.com

31. The Active Sun • Solar luminosity is nearly constant. • Very slight fluctuations. • 11-year cycle of activity. www.assignmentpoint.com

32. Solar Cycle • Increase in Coronal holes • Increase in solar wind activity - Coronal Mass Ejections • Increase in Auroral displays on Earth • Increase in disruptions on and around Earth. www.assignmentpoint.com

33. 11-year sunspot cycle. • Center – Umbra: 4500 K • Edge – Penumbra: 5500 K • Photosphere: 5800 K Sunspots www.assignmentpoint.com

34. Can see that Sun doesn’t rotate as a solid body? • Equator rotates faster. • This differential rotation leads to complications in the Solar magnetic field. www.assignmentpoint.com

35. Magnetic fields and Sunspots • At kinks, disruption in convection cells. • Sunspots form. www.assignmentpoint.com

36. Magnetic fields and Sunspots • Sunspots come in pairs. • Opposite orientation in North and South. • Every other cycle the magnetic fields switch. www.assignmentpoint.com

37. Sunspot Numbers www.assignmentpoint.com

38. Active Regions • Areas around sunspots give rise to the prominences www.assignmentpoint.com