Transcript The Solar Cycle

The Sun – Our Nearest Star
Surrounding the visible photosphere is the chromosphere. What you
see in this next video clip is the chromosphere. Each of the granules
you see are about the size of Texas. Granules change in a churning
kind of motion.
Chromosphere Convection and Granules
The surface of the sun is 5000o C , the temperature of the corona is
2,000,000o C. (It is not understood what causes this increase.)
The process of joining small nuclei together to make a larger nucleus
is called fusion. The process of breaking a large nucleus into smaller
nuclei is called fission.
Fusion
Fission
H
Fe
U
Because it has the most binding energy per nucleon, iron (Fe) is the
most stable element.
H
Fe
U
The Proton-Proton Chain – How Our Sun "Burns"
The three step proton-proton cycle can be written symbolically as:
1) 11H  11H  21H  e    e
2) 21H  11H  23He and e   e   
3) 23He  23He  42 He  2 11H
Notice that the first two reactions must occur twice in order to produce
the two Helium-3 nuclei needed for the third reaction. We can write the
net process as:
4 11H  42 He  2   2  ENERGY
Proton-proton Cycle
Solar Fusion In the proton–proton chain, a total of six protons (and two electrons) are
converted to two protons, one helium-4 nucleus, and two neutrinos. Neutrinos are chargeless
(i.e. neutral), very light – almost massless – particles. The two leftover protons are available
as fuel for new proton–proton reactions, so the net effect is that four protons are fused to form
one Helium-4 nucleus. Energy, in the form of gamma rays, is produced at each stage.
The energy given off in this reaction can be found by determining the
amount of mass converted to energy. This is found by finding the
difference in mass between the two sides of the equation and
multiplying it by 931.5 MeV per atomic mass unit (i.e. E=mc2). For
example, the mass of a proton is 1.007825 u, while the mass of the
helium-4 nucleus is 4.002603 u. So we have
Q  (mi  mf )  c2  4  (1.007825 u )  4.002603 u  931.5 MeV  26.7 MeV
Since the Sun radiates about 2 x 1039 MeV/s, that means there are
about 1038 fusion reactions per second, "consuming" 4 x 1038 protons
per second. So the mass of the Sun decreases by about 670 billion
kilograms per second, or almost 1.5 trillion pounds, due to the fusion
process!
Don't worry…the Sun has about 1057 protons - enough to burn for the
next few billion years. 
The Solar Neutrino Problem
Back when your instructor was working on his undergraduate degree, one of the
biggest puzzles in high energy physics and astrophysics was that the number of
solar neutrinos reaching Earth was substantially less (by 30 to 50 percent) than
the prediction of the Standard Solar Model. This discrepancy was known as
the solar neutrino problem.
If neutrinos do have a minute amount of mass, theory indicates that it may be
possible for them to change their properties, even to transform into other
particles, during their eight-minute flight from the solar core to Earth, through a
process known as neutrino oscillations. So neutrinos could turn into
something else (in particle-physics jargon, they are said to “oscillate” into other
particles) on their way to Earth and so go undetected.
In June 1998 the Japenese group operating the Super Kamiokande detector
reported the first experimental evidence of neutrino oscillations. Then in June
2001, measurements made at the Sudbury Neutrino Observatory (SNO) in
Ontario, Canada, revealed strong evidence for the type of neutrinos into which
the Sun’s neutrinos have been transformed. The total numbers of neutrinos
observed were completely consistent with the Standard Solar Model.
Apparently the solar neutrino problem has at last been solved!
The dominant thermonuclear reaction in a star changes with
temperature. For example, common reactions include:
MIN. TEMP.
REACTION
8 x 106 K
proton-proton chain
20 x 106 K
CNO cycle
100 x 106 K
triple alpha
600 x 106 K
carbon-helium fusion
109 K
carbon burning
The CNO Cycle
These six steps are termed the CNO cycle. Aside from the products
of radiation, positrons and neutrinos, notice that no carbon is
actually consumed in this process!
1) 12 C  11H  13 N  energy
2) 13 N  13 C  e    e
3) 13 C  11H  14 N  energy
4) 14 N  11H  15 O  energy
5) 15 O  15 N  e    e
6) 15 N  11H  12 C  4 42 He
12
C  4 11H  12 C  42 He  2 e  2 e  ENERGY (  rays )
Triple-Alpha Process
This process of Helium fusion in stars is called the triple-alpha
process. The helium nucleus (4He) is known as an alpha particle.
1) 4 He  4 He  8 Be  energy
2) 8 Be  4 He  12 C  energy
3 4 He  12 C  energy
Carbon-Helium Fusion
At much hotter temperatures, the star may actually combine carbon
and helium to make oxygen. This is called carbon-helium fusion.
12
C  4 He  16 O  ENERGY (  rays )
Carbon Burning
Some very large stars may become hot enough and have the right
conditions to facilitate the carbon burning process. For example:
12
C  12 C  24 Mg  energy
12
C  12 C  23 Na  11H  energy
12
C  12 C  20 Ne  4 He  energy
12
C  12 C  23 Mg  01n  energy
12
C  12 C  16 O  2 4 He  energy
Carbon burning requires a temperature of about a billion Kelvin to
overcome the vary large repulsion between the two positively
charged carbon nuclei.
The Solar Cycle
A sunspot is an Earth-sized dark blemish found on the surface of the
Sun. The dark color of the sunspot indicates that it is a region of lower
temperature than its surroundings. Sunspots are caused by magnetic
disturbances that occur in the Sun. They are magnetic storms on the
Sun.
The average number of sunspots reaches a maximum every 11 or so
years, then falls off almost to zero before the cycle begins afresh. The
latitudes at which sunspots appear vary as the sunspot cycle progresses.
Individual sunspots do not move up or down in latitude, but new spots
appear closer to the equator as older ones at higher latitudes fade away.
In fact, the 11-year sunspot cycle is only half of a 22-year solar cycle.
For the first 11 years of the solar cycle, the leading spots of all sunspot
pairs in the same solar hemisphere have one magnetic polarity, and
spots in the other hemisphere have the opposite magnetic polarity. These
polarities then reverse for the next 11 years.
Solar Cycle
Sunspot Cycle (a) Annual number of sunspots throughout the twentieth century, showing fiveyear averages of annual data to make long-term trends more evident. The (roughly) 11-year
solar cycle is clearly visible. At the time of minimum solar activity, hardly any sunspots are
seen. About four years later, at the time of maximum solar activity, as many as 200 spots are
observed per year. (b) Sunspots cluster at high latitudes when solar activity is at a minimum.
They appear at lower and lower latitudes as the number of sunspots peaks. They are again
prominent near the Sun’s equator as solar minimum is again approached. The most recent
solar maximum occurred in 2001.
Prominences, Flares, and Cornonal Mass Ejections
Sunspots are relatively gentle aspects of solar activity. However, the photosphere
surrounding them occasionally erupts violently, spewing forth into the corona large
quantities of energetic particles. The sites of these explosive events are known
simply as active regions.
A prominence is a loop or sheet of glowing gas ejected from an active region on
the solar surface, which then moves through the inner parts of the corona under
the influence of the Sun's magnetic field. Magnetic instabilities in the strong fields
found in and near sunspot groups may cause the prominences, although the
details are still not completely understood.
Flares are another type of solar activity observed near active regions. Also the
result of magnetic instabilities, flares are much more violent (and even less well
understood) than prominences. So energetic are these cataclysmic explosions
that some researchers have likened them to bombs exploding in the lower regions
of the Sun’s atmosphere. Unlike the trapped gas that makes up the characteristic
loop of a prominence, the particles produced by a flare are so energetic that the
Sun’s magnetic field is unable to hold them and shepherd them back to the
surface. Instead, the particles are simply blasted into space by the violence of the
explosion.
The Sun rotates about every 27 days.
Solar Activity and Rotation
Solar Activity I
Solar Activity II
Solar Prominence
Solar Flares in an Active Region of the Sun
A coronal mass ejection from the Sun is sometimes (but not always)
associated with flares and prominences. These phenomena are giant
magnetic “bubbles” of ionized gas that separate from the rest of the
solar atmosphere and escape into interplanetary space. Carrying an
enormous amount of energy, they can—if their fields are properly
oriented—connect with Earth’s magnetic field, dumping some of their
energy into the magnetosphere and potentially causing communications
and power disruptions on our planet. Such ejections occur about once
per week at times of sunspot minimum, but up to two or three times per
day at solar maximum.
Coronal Mass Ejection
Auroral StormI
Auroral Storm II
Aurora