Visible Image of the Sun

1. The Sun Visible Image of the Sun • Our sole source of light and heat in the solar system • A very common star:a glowing ball of gas held together by its own gravity and powered by nuclear fusion at its center.

2. Pressure (from heat caused by nuclear reactions) balances the gravitational pull toward the Sun’s center. Called “Hydrostatic Equilibrium. This balance leads to a spherical ball of gas, called the Sun. What would happen if the nuclear reactions (“burning”) stopped?

3. Made of … 71% Hydrogen 27% Helium 2 % heavier elements Information know from sun spectroscopy

4. Main Regions of the Sun

6. The Moon’s orbit around the Earth would easily fit within the Sun! Solar Properties Radius = 696,000 km (100 times Earth) Mass = 2 x 1030 kg (300,000 times Earth) Av. Density = 1410 kg/m3 Rotation Period = 24.9 days (equator) 29.8 days (poles) Surface temp = 5780 K

8. m= 4 p2 a3 G P2 n n n Calculating the mass of the Sun

9. m= 4 p2 a3 G P2 n n n a= orbit radius in AU (convert AU to meters) 1 AU = 1.5x1011m

10. m= 4 p2 a3 G P2 n n n G=gravitational constant G= 6.67x10-11 m3 kg sec2 n

11. m= 4 p2 a3 G P2 n n n P=revolution period (time) in seconds

12. m= 4 p2 a3 G P2 n n n G=gravitational constant G= 6.67x10-11 m3 kg sec2 n a= orbit radius in AU (convert AU to meters) 1 AU = 1.5x1011m Example #1 On Earth P=revolution period (time) in seconds

13. Example #2 Pg. 346 Problem #2 m= 4 p2 a3 G P2 n n n G=gravitational constant G= 6.67x10-11 m3 kg sec2 n a= orbit radius in AU (convert AU to meters) 1 AU = 1.5x1011m P=revolution period (time) in seconds

14. Example #3 SATURN 9.6 AU 29.46 years m= 4 p2 a3 G P2 n n n G=gravitational constant G= 6.67x10-11 m3 kg sec2 n a= orbit radius in AU (convert AU to meters) 1 AU = 1.5x1011m P=revolution period (time) in seconds

15. Luminosity of the Sun = LSUN (Total light energy emitted per second) ~ 4 x 1026W 100 billion one-megaton nuclear bombs every second!

16. The Solar Interior “Helioseismology” • In the 1960s, it was discovered that the surface of the Sun vibrates like a bell • Internal pressure waves reflect off the photosphere • Analysis of the surface patterns of these waves tell us about the inside of the Sun How do we know the interior structure of the Sun?

17. The Standard Solar Model

18. Energy Transport within the Sun • Extremely hot core - ionized gas • No electrons left on atoms to capture photons - core/interior is transparent to light (radiation zone) • Temperature falls further from core - more and more non-ionized atoms capture the photons - gas becomes opaque to light in the convection zone • The low density in the photosphere makes it transparent to light - radiation takes over again

19. Convection • Convection takes over when the gas is too opaque for radiative energy transport. • Hot gas is less dense and rises (or “floats,” like a hot air balloon or a beach ball in a pool). • Cool gas is more dense and sinks

20. Solar GranulationEvidence for Convection • Solar Granules are the tops of convection cells. • Bright regions are where hot material is upwelling (1000 km across). • Dark regions are where cooler material is sinking. • Material rises/sinks @ ~1 km/sec (2200 mph; Doppler).

21. Chromosphere

22. Chromosphere (seen during full Solar eclipse) • Chromosphere emits very little light because it is of low density • Reddish hue due to emission from Hydrogen

23. SOHO SPECTROHELIOGRAMSTODAY

24. Solar Wind & Corona

25. Corona (seen during full Solar eclipse) Hot coronal gas escapes the Sun  Solar wind

26. Solar Wind • Coronal gas has enough heat (kinetic) energy to escape the Sun’s gravity. • The Sun is evaporating via this “wind”. • Solar wind travels at ~500 km/s, reaching Earth in ~3 days • The Sun loses about 1 million tons of matter each second! • However, over the Sun’s lifetime, it has lost only ~0.1% of its total mass. CME Video & Activity

27. Coronal holes are sources of the solar wind (lower density regions) Hot coronal gas (~1,000,000 K) emits mostly in X-rays. Coronal holes are related to the Sun’s magnetic field Corona is HOTTER than the photosphere

28. The Active Sun UV light Most of the Solar luminosity is continuous photosphere emission. But, there is an irregular component

29. Sunspots (video) Granulation around sunspot

30. Sunspots • Typically about 10000 km across • At any time, the sun may have hundreds or none • Dark color because they are cooler than photospheric gas (4500K in darkest parts) • Each spot can last from a few days to a few months • Galileo observed these spots and realized the sun is rotating differentially (faster at the poles, slower at the equator)

31. Sunspots… what’s really happening? • Typical Sunspot seen in the visible light spectrum

32. Sunspots… what’s really happening? • Same image seen using x-rays

33. Sunspots & Magnetic Fields • The magnetic field in a sunspot is 1000x greater than the surrounding area • Sunspots are almost always in pairs at the same latitude with each member having opposite polarity • All sunspots in the same hemisphere have the same magnetic configuration

35. The Sun’s differential rotation distorts the magnetic field lines The twisted and tangled field lines occasionally get kinked, causing the field strength to increase “tube” of lines bursts through atmosphere creating sunspot pair

36. Sunspot Cycle Solar maximum is reached every ~11 years Solar Cycle is 22 years long – direction of magnetic field polarity flips every 11 years (back to original orientation every 22 years)

39. Heating of the Corona • Charged particles (mostly protons and electrons) are accelerated along magnetic field “lines” above sunspots. • This type of activity, not light energy, heats the corona.

40. Charged particles follow magnetic fields between sunspots: Solar Prominences Sunspots are cool, but the gas above them is hot!

41. Earth Solar Prominence Typical size is 100,000 km May persist for days or weeks

42. Very large solar prominence (1/2 million km across base, i.e. 39 Earth diameters) taken from Skylab in UV light.

43. Solar Flare and Resulting Prominence

46. Solar Flare, Prominence and Filament

47. Coronal activity increases with the number of sunspots.

48. SOLAR-TERRESTRIAL RELATIONSHIPS • AURORAE

49. Nuclear Fusion 4 H He The Proton-Proton Chain: What makes the Sun shine?

50. E = mc 2 (c = speed of light) But where does the Energy come from? • c2 is a very large number! • A little mass equals a LOT of energy. Example: • 1 gram of matter  1014 Joules (J) of energy. • Enough to power a 100 Watt light bulb for ~32,000 years!