1. The Sun

2. Layers of the Sun _____ - ~15 million K, 25% radius
__________ zone ~60% radius
________________ – to the surface
__________ (visible surface) ~5800K
Limb darkening
Sun spots
____________ - ~10,000K – very thin
_______ - may be several million K
Core
Radiative
Convective Zone
Photosphere
Chromosphere
Corona

4. The Sun’s Atmosphere
Photosphere – temp. ______ (average) Layer we see – the surface
Chromosphere – a thin layer, a few 1000 km thick, at a temperature between _______________. Can be seen during _____________.
Corona – ______________, 1,000,000 km thick, at a temperature of about ___________.
5800 K
4,000 – 10,000 K
solar eclipses
Outermost layer
1,000,000 K

5. Outer layers of sun
1 = photosphere, 2 = chromosphere, 3 = corona

6. Photosphere

7. Granulation
Convection Zone

8. Limb Darkening

9. Limb darkening

10. the “surface” of the sun
“Free streaming”
photons travel
to us without
running into
much matter
“Photosphere”
the “surface” of the sun
-- where the photons
we see emerge from
the sun and start
to “free stream”
“Random Walk”
in the interior of the sun,
photons are constantly
absorbed and scattered by matter

11. Sunspots are low temperature regions in the photosphere
________ are about 4000 K (2000 K cooler than solar surface) and have ______________ up 1000 the normal solar magnetic field. They can be as large as 50,000 km and last for ___________.
Sunspots
magnetic fields
many months

12. Sunspots are low temperature regions in the photosphere
The large _____________ in sunspots decrease the flow of heat via convection causing the _____________________.
magnetic fields
sunspot to become cool

14. Sunspots
Umbra
Penumbra
Granulation

15. Sunspot cycle

16. Sunspots can be used to measure the rotation of the Sun
Near the ______ the Sun rotates once in ________.
The _____ rotate more slowly, about once every ___ ____.
equator
25 days
poles 36
days

17. Chromosphere

18. Corona

19. Corona “heats up” over a very small distance

20. Solar Magnetic Field Existence of a ___________ & its complex
structure is because of the ________________
and __________ in the atmosphere
hot corona
solar magnetic field
vibrations
cartoon of magnetic
field lines on sun
X-ray pictures
of Sun

21. Magnetic field loops – SOHO satellite

22. Solar magnetic fields also create other phenomena
__________
______
________
_______ _____ _________
Prominences
Flares
Solar wind
Coronal
mass
ejections

23. Prominences - Cooler than photosphere.

24. Solar flares - Hotter, up to 40,000,000 K More energetic

25. Solar Flare
4K solar flare footage captured by NASA

26. Coronal mass ejections - eruption of gas, can reach Earth and affect aurora, satellites

27. Coronal mass ejection

28. “Northern Lights” (Aurora Borealis)
Particles in the solar wind slam into Earth’s atmosphere, ________________ Nitrogen & Oxygen which then __________, emitting the photons we see as _______.
collisions excite
de-excite
aurora

29. Sun at Different Wavelengths
Temperature
___________ determines which lines we see
Use to our advantage: if we look only at ____________ (wavelengths), we only see gas at certain temperatures – allows us to probe different parts of the sun (photosphere, chromosphere, corona, …)
certain lines

30. Sun at Different Wavelengths
6563 Angstroms -- H (Balmer) line of Hydrogen (tells us about _____________)
chromosphere

31. Sun at Different Wavelengths
195 Angstroms (UV) – _______________ ____________
transition region
and corona

32. Sun at Different Wavelengths
X-rays (______)
corona

33. The Sun’s Interior Structure
Photosphere
Energy transport via convection
Flow of energy
Energy transport via radiation
Energy generation via nuclear fusion
Temp, density and pressure decreases outward

34. The Sun’s Interior Core The region where _______ ______ takes place.
Temp. ~ 15 million degrees K.
Radiation Zone
______ is transported ______ primarily by ________.
Temp. ~ 10 million degrees K.
________________.
Convection Zone
______ is transported through _________.
nuclear
fusion
Energy
outward
photons
No nuclear fusion
Energy
convection

35. The Moon’s orbit around the Earth would easily fit within the Sun!

36. The Equilibrium Between Gravity and Pressure
The ____________ and ________ at the center of the Sun increases due to _____________________. Without a force to counter gravitation force, the Sun will continue to contract. However, once the condition for _____________ is reached, the energy released by the fusion process is enough to maintain a high enough temperature and pressure to __________________________.
That is, the gravitational force pulling
materials inward is balanced by
the outward force of thermal
pressure. This balance is maintained
until the nuclear fuel is exhausted.
temperature
density
gravitational contraction
nuclear fusion
resist the gravitational collapse

37. The Energy Source of the Sun
Today, we understand that the energy source of the Sun is the ___________________ which combines hydrogen nuclei to form helium. The increase of temperature at the center of the Sun due to gravitational contraction eventually triggers nuclear fusion, which converts some of the mass into energy, according to _____________________ ________________.
nuclear fusion process
Einstein’s mass-energy
equation, E = mc2
Electric charge is not conserved!
This is a simplified picture that’s not exactly correct.

38. Proton-Proton Chain

39. Why Does Nuclear Fusion Occurs Only at the Center of the Sun?
Temperature is a measurement of the average _____________ of the particles.
Gas at very ________________ move at very __________.
High speed is needed to overcome the __________ __________________ between the protons to get them very close to each other.
Once the protons are close to each other, the _____________ ______ can bind them together.
kinetic energy
high temperatures
high speeds
repulsive
electromagnetic force
strong nuclear
force

41. Fusion of Hydrogen into Helium E = mc2

42. E = m c 2 A little mass equals a LOT of energy. Example:
(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  Joules (J) of energy.
Enough to power a 100 Watt light bulb for ~32,000 years!

43. How does the energy generated at the center get to the surface and to us?
The ______ generated by the nuclear fusion process is _______ in the form of ______ (radiative energy). The photons interact with the solar plasma (mostly the electrons). Each time a photon encounters an electron, it _________________. Thus, the photons go through a ______ path to the surface.
energy
released
photons
changes its direction
zig-zag
It takes about 1 million years for a photon to travel from the center of the Sun to its surface.
The ‘random walk’ of photon to the surface.

45. Energy Transport within the Sun
Temperature falls farther from core - more and more non-ionized atoms capture the photons
Gas becomes opaque to light in the convection zone

46. Hot gas is less dense and rises
Convection
Convection takes over when the gas is too opaque for radiative energy transport.
Hot gas is less dense and rises
Cool gas is more dense and sinks

47. How do we Observe the Internal Structure of the Sun?
Almost all the ________ from the Sun originates from
the _________ of the Sun. To ‘see’ inside the Sun, we
need to use special observational methods:
______________.
________________________.
radiation
outer layers
Helioseismology
Solar Neutrino Observations
1. Helioseismology
The study of how the _______ of the Sun moves – expands and contracts, can tell us about the internal structure of the Sun.
We observe the ______ of the solar surface by observing the _____________ of light.
surface
motion
Doppler shift

48. Helioseismology Helioseismology
The study of how the surface of the Sun moves – expands and contracts, can tell us about the internal structure of the Sun. This is similar to how we study the internal structure of the Earth by studying how sound waves propagate through Earth.
The surface of the Sun is oscillating up and down due to the excitation of seismic waves.
We observe the motion of the solar surface by observing the Doppler shift of light from the surface of the Sun.
The red and blue patches represent regions of solar surface receding inward (red) and bulging outward (blue).
The surface of the Sun is oscillating up and down due to the excitation of seismic waves.
Different seismic wave travels through different part of the solar interior. Thus, by studying the behavior of the seismic waves, we can infer the internal structure of the Sun.
Paths of wave

49. Neutrino Observatories
Homestake Neutrino Detector in South Dakota, 1.5 km underground. Neutrino detectors are placed underground to shield them from other unwanted interaction with other cosmic ray particles.
Kamiokande Neutrino Detector, Japan
Sudbury Neutrino Observatory in Canada, 2 km underground. The 12 meter diameter tank contains 1,000 tons of heavy water.

50. Looking Under The Solar Surface – Neutrino Observation
Solar Neutrino Experiment – 2002 Nobel Price in Physics
Knowing how many neutrinos the proton-proton chain produces, we can predict how many neutrinos we can expect to see from the Sun.

51. The Solar Neutrino Problem
A type of elementary particle (_____ different flavors, actually) with very low mass and interacts only through the weak (nuclear) force
 Not easily detectable— From the many trillions of neutrinos passing through the neutrino detectors every second, only roughly one neutrino a day is expected to be recorded!
three

52. The Solar Neutrino Problem
Should observe one solar neutrino per day in neutrino detectors. Only get ____ solar neutrino every _____ days.
 Theory of the _______________________?
 We don’t really understand neutrinos?
There are ______ different types of neutrinos. Existing detectors only see ____ of the 3 types. Neutrinos ___________ into a different type of neutrino after they were generated, thus reducing the number of neutrinos detectable.
New neutrino detectors sensitive to all three.
Early results indicated that the number of solar neutrinos is consistent with our model of the Sun!
one
three
structure of the Sun is wrong
three
one
may change

53. http://phobos. physics. uiowa
Layers of the Sun 1 3
Structure of the Sun – The Internal Structure