1. Chapter 15 The Sun

2. Solar Prominence – photo by SOHO spacecraft
from the
Astronomy
Picture of
the Day site
link

3. SOHO (before launch, at ESA facility) (without solar panels)
Gallery of the
SOHO spacecraft:
SOHO spots 2000th comet

4. Solar and Heliospheric Observatory (SOHO) (link) is in orbit around the sun near the L1 point

5. STEREO mission – two spacecraft on opposite sides of the Sun
Each is in an orbit similar to Earth’s orbit, but one moves ahead of Earth, and the other trails behind Earth. The separation has been increasing over time.
The purpose is to continuously monitor the entire surface of the Sun, to help predict space weather (solar winds).

6. SOHO: Ultraviolet pictures of the Sun

7. The closest star - The Sun

8. The Sun is a layered structure

9. The atmosphere of the Sun
The outer layers are
all parts of the Sun’s
atmosphere:
Corona
Transition zone
Chromosphere
The Photosphere is the
“surface” of the Sun; it
emits the light that we see.
The Convection and Radiation Zones are named for
how energy is transported in the interior of the Sun.

10. Solar Granulation in the photosphere can be seen in movies taken by the SOHO cameras
This granulation shows
that convection is
occurring under the
surface of the Sun. On
average these granules
are about the size of a
large state like Texas
(up to 1000 miles across).

11. Above the granular photosphere is the chromosphere.

12. Solar spicules are relatively cool and hence dark features that appear above the chromosphere. These spicules are jets of gas that rise up above the chromosphere.

13. Absorption of various wavelength of light occurs in the solar chromosphere This region is usually only visible to us during a total solar eclipse. Also visible in this photo are prominences.

14. Next are the transition zone and the Solar Corona

15. The Solar Corona is most obvious during a total solar eclipse.

16. Coronal Hole, seen in X-ray images by Yohkoh.

17. Solar Atmospheric Temperature
So much energy is flowing
through this region and
the density is so low that
the temperature of these
regions is very high.
All of this energy causes
gas to “boil” off into space,
or causes gas to be
“pushed” off the surface
of the Sun. This gas is
called the Solar Wind.

18. Solar Spectrum in the visible region

19. Solar Spectrum
This absorption spectra
tells us what elements
are in the Sun’s
chromosphere and most
likely in the rest of the
Sun, except in the core.

21. Sunspots
Sunspots are cooler
regions of the Sun’s
surface

22. Sunspots are also regions of intense magnetic fields.
Sunspots, Up Close
Sunspots are also
regions of intense
magnetic fields.
Just like regular magnets,
sunspots come in pairs
one is a “North pole” and
one is a “South pole”
Dark region – umbra
(4300 K)
Brighter region – penumbra
(5000 K)
Granules – (5800 K)

25. Sunspot Magnetism

26. Sunspots behave somewhat like a horseshoe magnet, causing a magnetic field above the photosphere.

27. Above the sunspot, the magnet field causes the hot gas of the corona to concentrate along the field lines, seen here is a photo in the ultraviolet.

28. See next slide for detail

30. Solar Rotation
The Sun has Differential rotation which means
different parts of the Sun rotate at different speeds.
The Sun’s equator rotates faster than at the poles.

31. Solar Rotation “drags” the magnetic field around.
All of the sunspot pairs in the north hemisphere have the
same polarity or orientation. All of the sunspot pairs in the
southern hemisphere have the opposite polarity.

32. Sunspot Cycle
Both the number and the
location of the sunspots
change during the
Sunspot or Solar Cycle
which lasts 11 years

33. Maunder Minimum
The solar cycle has varied a lot in the past and
we still do not know all of the details of how it works.

34. An active corona occurs at the peak of the sunspot cycle.

35. Many Prominences, Flares, and Coronal Mass Ejections can be seen.
The “active Sun” refers to times when there are lots of sunspots and the surface of the Sun is very active in other ways.
Many Prominences, Flares,
and Coronal Mass Ejections
can be seen.
Also during this time the corona becomes larger and more irregularly shaped.
This year, 2018, we are in a
period of solar minimum. See

36. Solar Prominences are huge outbursts of hot gases that blow out into space, then often the gas cools and falls back into the Sun.

37. are loops of hot gas that rise from the surface of the sun. They are
Solar Prominences
Solar Prominences
are loops of hot gas that
rise from the surface
of the sun. They are
shaped by the magnetic
fields of the Sun.
SOHO website:
For Mar. 28, 2014, there is a movie of 8 CMEs in five days:

38. Solar Flares are much more rapid than prominences.

39. Solar Flare
A rapidly expanding "solar quake" on the Sun’s surface depicted here by the Michelson Doppler Imager (MDI). It immediately followed a solar flare on 1996 July 6 and spread out more than 100,000 km at the solar surface. Scientists have shown that solar flares produce seismic waves, and gigantic seismic quakes, in the Sun's interior. They have tracked these seismic waves and found that "sun-quakes" closely resemble earthquakes on our planet.

40. A Solar flare
on Nov. 11,
2003.
SOHO
obtained
numerous
images of
the active
Sun in
fall 2003.

41. Coronal Mass Ejection
Coronal Mass Ejection events (CME) is when an eruption on
the surface of the Sun ejects large amounts of gas into space.
These events are larger than solar flares and are less frequent.

42. Coronal Mass Ejections throw huge amounts of material into space, which can have effects on Earth if it hits us.

43. Coronal Mass Ejection (we’ll show movies) Also see www. spaceweather
Coronal Mass Ejection (we’ll show movies) Also see for recent news.

46. Solar Oscillations can be used to understand the interior of the sun in a way similar to seismological studies of the Earth; this is called Helioseismology. (link to GONG)

47. Helioseismology has been especially useful in understanding the region just under the photosphere. The core of the Sun has been modelled using theoretical physics calculations and data from nuclear experiments.

48. FIGURE 10-21 The Solar Model
(a) Thermonuclear reactions occur in
the Sun’s core, which extends to a
distance of 0.25 solar radius from the center. In this model,
energy from the core radiates outward to a distance of 0.8
solar radius. Convection is responsible for energy transport
in the Sun’s outer layers. (b) The Sun’s internal structure is
displayed here with graphs that show how the luminosity,
mass, temperature, and density vary with the distance from
the Sun’s center. A solar radius (the distance from the Sun’s
center to the photosphere) equals 696,000 km. (c) Ten most
common elements in the Sun, by the numbers of atoms of
each and by the percentage of the Sun’s total mass they
each comprise. (a: NASA)

49. ionized but the protons do not have enough velocity to hit each other
Nuclear fusion reactions occur at high temperature in the core, which causes particles to slam into each other at high speed.
At lower temperatures,
hydrogen atoms are
ionized but the protons
do not have enough
velocity to hit each other
because of electric force.
At higher temperatures,
the protons have more
velocity, so when they hit
each other they can fuse
together to form a nucleus
of deuterium (and a
positron and a neutrino).

50. Solar Fusion occurs in several reaction stages, all occurring simultaneously in the core of the Sun.

51. See details on following slides

53. Radiant energy from the core travels quickly outward
through the radiation zone to heat the convection zone.

55. FIGURE 10-21 The Solar Model
(a) Thermonuclear reactions occur in
the Sun’s core, which extends to a
distance of 0.25 solar radius from the center. In this model,
energy from the core radiates outward to a distance of 0.8
solar radius. Convection is responsible for energy transport
in the Sun’s outer layers. (b) The Sun’s internal structure is
displayed here with graphs that show how the luminosity,
mass, temperature, and density vary with the distance from
the Sun’s center. A solar radius (the distance from the Sun’s
center to the photosphere) equals 696,000 km. (c) Ten most
common elements in the Sun, by the numbers of atoms of
each and by the percentage of the Sun’s total mass they
each comprise. (a: NASA)

56. This neutrino detector near Kamioka, Japan, is called the Super-KamiokaNDE. (Kamioka Neutrino Detection Experiment) (Workers are seen inspecting the phototubes, with some of the water drained out of the large tank, which is deep underground.) This detects neutrinos from the core of the Sun.

57. A Solar Neutrino Experiment in the Sudbury Neutrino Observatory, in an
old nickel mine
near Sudbury,
Canada.
This and other
experiments confirm
the Solar Model
described on the
previous slides.
FIGURE The Solar Neutrino Experiment
Located 6800 feet underground in the Creighton nickel mine in
Sudbury, Canada, the Sudbury Neutrino Observatory is centered
around a tank that contains 1000 tons of water.
Occasionally, a neutrino entering the tank interacts with one
or another of the particles already there. Such interactions create
flashes of light, called Cerenkov radiation. Some 9600
light detectors sense this light. The numerous silver protrusions
are the back sides of the light detectors prior to their being
wired and connected to electronics in the lab, seen at the
bottom of the photograph. (Ernest Orlando Lawrence/Berkeley
National Laboratory)