Download Day 20 - Ch. 8

Chapter 9
The Sun
part 2
The closest star is the Sun
Solar Prominences (on upper right)
from the
Astronomy
Picture of
the Day site
link
(photo by
the SOHO
spacecraft)
The Sun is a layered structure
Vital Statistics of the Sun
•
•
•
•
Diameter is about 109 Earth diameters.
Mass is about 333,000 times Earth’s mass.
Surface temperature is about 5800 K (or 5500oC).
Rotation period is about 25 days at the equator and
35 days at the poles (differential rotation).
• Average density is about 1.4 times that of water.
• All the Sun’s energy is produced by fusion in a dense
core that is at about 15.5 million Kelvin (or Celsius).
• The energy travels outward through various zones.
• The thermonuclear core produces energy by nuclear
reactions which are caused by the high temperature,
hence “thermo-nuclear”. (more on this later)
• Much of the energy comes out of the core in the form
of X-rays or gamma rays, which travel without being
absorbed through the radiative zone, which is
transparent to these X-rays or gamma rays (g rays).
• The X-rays are then absorbed in the convective zone,
and this heats the plasma in that zone, which
undergoes convection, a motion which is similar to
convection in any hot fluid.
• The convective zone has very large convection cells,
and then above that zone is the photosphere, which
has smaller convection cells.
Nuclear fusion reactions occur at high temperature in the core,
which causes particles to slam into each other at high speed.
Below about 10 million K
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).
Nuclear fusion occurs in several reaction stages,
all occurring simultaneously in the core of the Sun.
The players in this drama
• Proton – the nucleus of a hydrogen atom, an elementary particle
with a positive electrical charge. (denoted by p or 1H)
• Neutron – another elementary particle, found in the nucleus of
heavier elements. A neutron is electrically neutral (zero charge).
• Electron – an elementary particle which normally orbits a
nucleus, but is moving freely in the high-temperature plasma of
the Sun. The electron has a negative electrical charge. (e-)
• Positron – the antiparticle to the electron, with the same mass
but a positive charge. (e+)
• Deuteron – nucleus of deuterium, consists of a proton and a
neutron bound together. (2H or D or d)
• Helium-3 – has 2 protons and 1 neutron in its nucleus. (3He)
• Helium-4 – has 2 protons and 2 neutrons in its nucleus. (4He)
• Neutrino – a very light particle with no electrical charge and the
ability to penetrate through ordinary matter easily. (greek nu n)
Nuclear reactions
• Nuclear reactions are distinct from chemical reactions.
• The difference is that chemical reactions combine atoms to form
molecules, and different molecules can react to form new ones,
• whereas nuclear reactions involve nuclei, composed of
elementary particles, and/or elementary particles themselves.
• An example is the proton-proton fusion reaction.
• Fusion means to join together.
• If two protons smash together at enough speed, they can fuse
together and form reaction products.
• The products are a deuteron, a positron, and a neutrino.
• All of these move away at high speed, which means there is a
form of energy called kinetic energy (energy of motion).
• In equation form: p + p --> d + e+ + n + energy
• The next slide show several other reactions.
See details on following slides
Radiant energy from the core travels quickly outward
through the radiation zone to heat the convection zone.
• Equivalently, the reactants could be four protons and
four electrons (i.e., four ionized hydrogen atoms), and
the products are one helium nucleus (also called an
alpha particle) which has two protons and two
neutrons, and two electrons (an ionized helium atom).
• Also produced is a large amount of kinetic energy (the
high speed of the reactants) and energy in the form of
gamma rays or X-rays that quickly leave the core.
• Another product is the neutrino. Large quantities are
produced, but they have little effect on the Sun
because they pass easily through large layers of
ordinary matter without being absorbed.
• However, the neutrinos need to be studied because
they can tell us something about the core of the Sun.
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.
Cross-section of
the Kamioka NDE
detector (which is
located in a mine).
The big tank is
filled with pure
water and the
walls have the
PMT tubes, to
detect light
from the
arrival of a
neutrino
The rare interaction of a neutrino with the water
will produce a burst of light which fans out in a
cone shape. This light is detected by a device
called a photomultiplier tube (PMT) and
recorded by computers for later analysis.
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.
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).
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.
Above the granular photosphere is the chromosphere.
The Solar
Corona is
most
obvious
during a total
solar eclipse.
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.
Coronal Hole, seen in X-ray images by Yohkoh. (link)
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.
Sunspots
Sunspots are cooler
regions of the Sun’s
surface
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)
Sunspot Magnetism
Sunspots behave somewhat like a horseshoe magnet,
causing a magnetic field above the photosphere.
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.
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
Sunspot Cycle
Both the number and the
location of the sunspots
change during the
Sunspot or Solar Cycle
which lasts 11 years
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.
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.
Solar Prominences are huge outbursts of hot gases
that blow out into space, then often the gas cools
and falls back into the Sun.
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:
http://sohowww.nascom.nasa.gov/
For Mar. 28, 2014, there is a
movie of 8 CMEs in five days:
http://sohowww.nascom.nasa.gov/pickoftheweek/
Solar Flares are much more rapid than prominences.
A Solar flare
on Nov. 11,
2003.
SOHO
obtained
numerous
images of
the active
Sun in
fall 2003.
Some vocabulary related to CMEs
• magnetopause - the boundary between the solar wind and the
region protected by the Earth's magnetic field
• magnetotail - the portion of the Earth's magnetic field that flows
away from Earth in the direction away from the Sun and
provides the largest source of particles that cause the aurora
• bow shock - similar to the type of wave that builds up in front of
the bow of a boat
• Carrington event of 1859 - a strong CME hit Earth and caused
sparking of telegraph equipment due to electric effects in the
long wires strung between cities of that era. For more on this
see Wikipedia https://en.wikipedia.org/wiki/Solar_storm_of_1859
• Space Weather Prediction Center http://www.swpc.noaa.gov/
• SpaceWeather.com has links to several related sites
Videos about CMEs and solar flares
• The difference between flares and CMEs is shown here:
•
http://www.nasa.gov/content/goddard/the-difference-between-flares-and-cmes/
• The strong CME of July 2012 is described in a video at
•
http://www.nasa.gov/goddard/mapping-the-journey-of-a-giant-coronal-mass-ejection/
• which mentions coronagraphs, which block light from the Sun’s
photosphere to allow taking pictures of surrounding space.
• Simulations of the effect of a CME on the Earth's magnetic field
is shown in a video at
• http://www.nasa.gov/content/goddard/how-nasa-watches-cmes/
• or on YouTube at
https://www.youtube.com/watch?v=cLLq6plMjU0
• Carrington event of 1859 - a strong CME hit Earth and caused
sparking of telegraph equipment due to electric effects in the
long wires strung between cities of that era. For more on this
see Wikipedia https://en.wikipedia.org/wiki/Solar_storm_of_1859
Exam # 3 will be on Thursday, April 6. That’s this week.
It will cover Ch. 7, 8, and 9 in the Comins textbook and
have a format similar to the previous exams.
Or, if you use the OpenStax book, see the review
sections of the chapters which correspond to this
material. The corresponding sections are 11.1-3, 12.15, 13.1-4, 14.1-2, 15.1-4, 16.1-4.
I will review for about half an hour before starting the
exam.