1. Previous Classes: This Class Upcoming Classes Stars Exoplanets The Sun
Phys 1830: Lecture 25
NASA’s Solar Dynamics Observatory: Extreme UltraViolet wavelengths
VW date today – new password Friday.
Previous Classes:
Exoplanets
This Class
The Sun
Upcoming Classes
Stars
Luminosity
Radii, Mass
Lifetime
Stellar Populations
ALL NOTES COPYRIGHT JAYANNE ENGLISH
Focus on SOHO images unless otherwise stated.
Inverted, false colour H_alpha image. Alan Friedman.
Office hours Monday Nov 18. 3:00-4:00pm.
Take up YOUR test during week.

2. Draw the components of the Sun.
Pass to your neighbour for marking

3. The Sun The photosphere is the visible "surface" of the Sun.
Below it lie the convection zone, the radiation zone, and the core.
Above the photosphere, the solar atmosphere consists of the chromosphere, the transition zone, and the corona

4. Stars like our sun are in hydrostatic equilibrium.
The Sun’s Interior
Thus the sun doesn’t explode outward nor collapse inward.
Stars like our sun are in hydrostatic equilibrium.
Stable balance between the opposing forces of gravity and pressure from hot gas.
How is the gas heated?

5. Requires high temperature (~15 million K)  “thermo”
The Sun’s Core
Only one known energy generating mechanism can account for the Sun’s enormous energy output:
Thermonuclear Fusion
Requires high temperature (~15 million K)  “thermo”
Fuse H nuclei into Helium nuclei in a nuclear reaction converting a tiny amount of mass into energy.
 “nuclear”, “fusion”
If you want more detail about the reaction, look up the Proton-Proton Chain.

6. The Sun’s Core
The thermonuclear reaction in the core is the Proton-Proton Chain
produces anti-matter which annihilates with normal matter generating energy (gamma-rays)
also generates neutrinos (detections at Sudbury Neutrino Observatory confirm this scenario).
Enough H in core to have burned for 4.5 billion years to date and can continue for another 5-6 billion years.

7. Figure 16-9 Astronomy Today
The Sun’s Interior: Transportation of Energy Outwards
Figure 16-9 Astronomy Today
Radiation Zone: Ionized state. Energy from core causes separation of electrons from protons which generates photons which are absorbed by atoms. The separation and creation plus absorption of photons repeats.
Physical transport of energy in the Sun's convection zone. We can visualize the upper interior as a boiling, seething sea of gas. Near the surface, each convective cell is about 1000 km across. The sizes of the convective cells become progressively larger at greater depths, reaching some 30,000 km in diameter at the base of the convection zone, 200,000 km below the photosphere. (This is a highly simplified diagram; there are many different cell sizes, and they are not so neatly arranged.)
Photosphere: electron drops from an excited state to a lower energy level generating photons. These can now escape.
Convection Zone: Excited state.Temperature has dropped so electrons recombine with atoms and photons absorbed. This zone is opaque since photons are not escaping.
Photosphere: Less dense so photons can escape. Radiation again.

8. Figure 16-9 Astronomy Today
The Sun’s Interior: Transportation of Energy Outwards
Figure 16-9 Astronomy Today
Neutrinos can escape from the core within minutes.
Photons are absorbed and re-emitted repeatedly. It takes about 170,000 to a million years for a photon to escape according to different estimates.
Photons will also have less energy further away from the core, so there is a change of wavelength with stellar radius  peak of blackbody radiation in the yellow range of the spectrum rather than gamma-rays.
See for why there is a large uncertainty in how long it takes.

9. Question 3 The Sun is stable as a star because
1) gravity balances forces from pressure.
2) the rate of fusion equals the rate of fission.
3) radiation and convection balance.
4) mass is converted into energy.
5) fusion doesn’t depend on temperature.
The Sun is stable as a star because
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10. Question 3 The Sun is stable as a star because
1) gravity balances forces from pressure.
2) the rate of fusion equals the rate of fission.
3) radiation and convection balance.
4) mass is converted into energy.
5) fusion doesn’t depend on temperature.
The Sun is stable as a star because
The principle of Hydrostatic Equilibrium explains how stars maintain their stability.

11. Question 1
1) core
2) corona
3) photosphere
4) chromosphere
5) convection zone
The visible light we see from our Sun comes from which part?
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12. Question 1
1) core
2) corona
3) photosphere
4) chromosphere
5) convection zone
The visible light we see from our Sun comes from which part?
The photosphere is a relatively narrow layer below the chromosphere and corona, with an average temperature of about 6000 K.

13. Figure 16-10 Solar Granulation of the Photosphere
The Sun’s Surface
Photograph of the granulated solar photosphere, taken from the Skylab space station looking directly down on the Sun's surface. Typical solar granules are comparable in size to a large U.S. state. The bright portions of the image are regions where hot material is upwelling from below. The dark regions correspond to cooler gas that is sinking back down into the interior. The inset shows a perpendicular cut through the solar surface. (Big Bear Solar Observatory)

14. The Sun’s Surface
KIS/SVST (La Palma)
The sizes of the granules range from approx. 250 km to more than 2000 km, with an average diameter of 1300 km.
(height MB = 1225 km; width southern MB ~ 450 km)
Lifetimes of granules typically range from 8 to 15 minutes. (This is a sped up 35min movie.)
Horizontal and vertical velocities of the gas motion are 1 to 2 km/s.
lower size limit set by the telescope and the Earth's atmosphere (seeing).

15. Table 16-1 The Standard Solar Model
As expected, the core where energy is produced is hot and then the sun cools with distance from this engine.
Unexpectedly the atmospheric temperature increases with distance!
Probably caused by disturbances in the Sun’s magnetic field.

16. The Sun The photosphere is the visible "surface" of the Sun.
Below it lie the convection zone, the radiation zone, and the core.
Above the photosphere, the solar atmosphere consists of the chromosphere, the transition zone, and the corona

17. Upper Chromosphere
Same day at optical wavelengths..
EIT detector on SOHO
0C = 273K
Each wavelength probes an excited or ionized state of specific elements. These states occur at certain temperatures. The temperatures are associated with heights above the photosphere. Thus each wavelength range probes a different height in the atmosphere of the Sun.
UV at 304 angstroms.
60,000 C.
Notice how some of the activity in the atmosphere is correlated with the sunspots.

18. Lower Corona
171 angstrom
1 million degrees C

19. Higher in the Corona
195 angstrom
1.5 million C

20. Upper Corona
284 angstroms
3 million C

21. UV of Corona
A == angstrom.
171 A, 195 A, 284A.

22. Activity in the Atmosphere is Related to Sunspots on Photosphere.

23. Sunspots: Swedish Solar Telescope
Swedish Solar Telescope
The high resolution image was achieved using sophisticated adaptive optics, digital image stacking, and other processing techniques to counter the blurring effect of Earth's atmosphere.

24. Sunspots
Helioseismology --> depth
time-distance helioseismology, i.e., measuring travel time for a wave along a path, is similar to how we monitor and measure earthquakes on Earth.
Darkest part of spot on the right is about the diameter of the earth.
Dark because they are a cooler temperature (4500K) compared to surrounding photosphere (5800K).
Spectra  magnetic field is 1000x photosphere.
Sunspots’ magnetic field interfere with the normal flow of hot gas towards the surface
 cooler sunspot.

25. Sunspots: Differential Rotation
By observing sunspots
gas at the equator rotates once in about 25 days.
Gas at poles rotates once in about 30 days.

26. Sunspots
TRACE satellite
Image b is inverted in intensity – the darkest regions are the hottest.
Sunspots are in pairs, linked by magnetic field lines emerging from one and re-entering the sun in the other.
Superheated gas (plasma) flows along the magnetic field lines forming loops in the Far UV image (bottom right).

27. Spicules
Follow links to video!
Magnetic field tubes filled with gas jetting into chromosphere.
Associated with active regions, such as the sunspot on the left.
Probably due to churning in Sun’s outer layers.

28. Solar Dynamics Observatory
To find this google: “NASA SDO rain on sun”
Solar “rain” traces B field lines.

29. Generating Sunspots Twisting in the global magnetic field is caused by
SOHO/ESA/NASA
BY OBSERVING SUNSPOTS, we see that the gas at equator rotates once every 25 days while at the pole it rotates every 30 days. This is called “differential” rotation.
Convection causes twists.
Magnetic field is currently generated by a dynamo --- motion in the interior causes an electric current which generates a magnetic field. An example of a dynamo is a bicycle light that works when you peddle the bike, generating an electric current.
Twisting in the global magnetic field is caused by
differential rotation with latitude.
Convection of the magnetized gas.
Dynamo

30. Sunspot Cycle
Sunspot maximum is next expected around May 2013.
This cycle of the magnetic field wrapping, unwrapping and starting to wrap again takes roughly 11 years.

31. Review Question
As the Sun rotates, an individual sunspot can be tracked across its face. From eastern to western limb, this takes about
A) 12 hours.
B) a week.
C) two weeks.
D) a month.
E) 5.5 years.

32. Extensions up to 10 times the diameter of Earth.
Prominences
From here – without tornados and slide 38.
Loops or sheets of plasma trace the magnetic field lines in or near sunspots.
Extensions up to 10 times the diameter of Earth.
Last for days or weeks.

33. Solar Flares and Coronal Mass Ejections
If you see it in UV it is in the 10,000s degrees K through millions degrees K range. In the millions degree K it will also be seen in X-ray. E.g. check out Hinode X-ray Telescope (XRT).
Prominences and solar flares are initiated in the lower atmosphere since they are associated with active regions. Flares are thought to occur when the loops between sunspots twist and suddenly snap – this is so cataclysmic that it generates proton showers and gamma-rays.
See
Green: solar flare -- can also be seen in X-ray (100 million K)
Flash across region in minutes and blast into space.
Red: coronal mass ejection
Giant magnetic bubbles of ionized gas separating from the solar atmosphere.
Occur weekly at sunspot mininum and a few times a day at maximum.
Blue: proton shower – recall fast moving particles are called cosmic rays.

34. Solar Wind
Radiation takes 8 minutes to reach Earth; particles take a few days.
Continous stream of electromagnetic radiation and cosmic rays.
from high in corona where gas is hot enough to escape.
From coronal holes – regions where magnetic field loops snap and extend into space.

35. SDO – 2 instruments & many filters  stellar components
Solar Dynamics Observatory (SDO)

36. Solar Dynamics Observatory: Giant Tornadoes

37. High Resolution Coronal Imager (Hi-C telescope)
On a sounding rocket
energy pumped into corona when:
braids release
B fld lines cross

38. SDO