Title: The Sun
1The Sun A Typical Star
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- The layers of the sun core, radiative zone,
convective zone, photosphere, chromosphere, and
corona - Sunspots and magnetic fields, the sunspot cycle
- Solar activity and how it influences the Earth
2Gravity vs. pressure
3A Star A Balance between Gravity and Pressure
- Self-regulating
- Higher fusion rate would expand star, lowering
cores self-gravity and thence density,
pressure, temperature and thus lowering fusion
rate. And vice versa
4Sun layers
5Layers of the sun
6- Core where temperature exceeds fusion point (10
million Kelvin) - Radiative Zone nothing much goes on here. It
just acts as an obstacle course for the photons
created in the core and random-walking their way
upward - Convection Zone temperature gradient is so
steep that photon diffusion cant carry the heat
outward fast enough. The rising temperature
expands the gas, lowering density and causing it
to rise (helium-balloon-like) to the surface,
where it cools, gets denser, and falls back down
to get reheated and start all over again. Think
soup cooking on a stove. - Photosphere visible surface. This is where the
mean free path now gets so long the material is
transparent above here.
7Sunspots optical
8Sunspots
- Places where the suns magnetic field is
concentrated and inhibits the normal convective
flow of hot material from below. So the material
sits on the surface and cools off as it radiates
to the sky. - Charged particles in a magnetic field feel a
force sideways to their motion, binding the gas
to the field. - Sunspots are like magnetic scabs of gas unable
to be recirculated to lower, hotter levels. They
are bound to the magnetic fields in the
photosphere, cooling as they radiate to the cold
universe, and hence cool off and darken. - Vertical structure of a sunspot
9HiRes sunspot
10Sunspot in UV light. Note magnetic field lines
11Earth w/ sunspot
12Marching sunspots
13Sunspot cycle 1760-1965
14Sunspot cycle vs time
15Solar Maxima have been decreasing for decades
16Solar Physics has advanced to the point of being
able to make rough predictions of solar activity
17Sun pic at max,min
18How Does The Solar Cycle Affect Earth?
- Two important ways
- 1. The solar wind creates aurorae (more later)
- 2. Solar luminosity changes during the cycle. We
have seen that lower solar activity goes with
lower average temperatures on Earth
19How Does Solar Activity Change Solar Luminosity?
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- Higher solar activity produces higher solar
luminosity. - Mechanism more surface magnetic field energy,
which thermalizes (i.e. becomes random kinetic
energy, as the 2nd Law of Thermodynamics
requires) and produces more net solar radiation. - Some of the magnetic field energy directly
impacts Earth by high speed solar wind particles
hitting Earth. - However, the luminosity changes are tiny less
than 0.1, as measured by satellites above the
atmosphere.
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23Maunder Minimum The Little Ice Age Connected?
- The Maunder Minimum in sunspot numbers
corresponds to a cool period in climate on Earth. - The cooler climate is very likely caused in part
by the lower solar activity, but only in part, as
the direct solar luminosity changes are too
small. - The Little Ice Age also corresponds to a period
of unusually intense volcanic activity, and also
to the time when human population dropped by 20
due to the Plague and mass loss of life in the
New World due to transported disease leading to
reforestation which lowered CO2 levels. - However, the exact apportionment to these
differing causes is not well constrained by the
data - Regardless, solar activity changes cannot be
responsible for the climate change of the past 60
years, for multiple reasons well discuss later
24The most intensely spotted star yet discovered
and discovered right here at Cabrillo Observatory!
25chromosphere
26Chromosphere all around
27Diamond ring
28Total eclipse corona
29Eclipse composite
30Total eclipse corona
31Powerful solar flare
32cme
33solarwind
34Sun Halpha big prominence
35Sun halpha big prom later
36EarthOnionMagField
37Earth magnetosphere
38SOHO wide angle
39Aurorae GiNormous Flourescent Lights!
- Caused when high speed solar wind particles
impact the Earths atmosphere - Collisionally excites the nitrogen and oxygen
atoms - These atoms then de-excite (electrons fall back
down through the energy levels) giving off
photons - Exactly the same as how flourescent lights work!
40greenpurpleAurora
41Aurora westlake
42Aurora lindersen
43Aurora hoffman
44Aurora c/IkeyaZhang
45Aurora ewoldt
46Aurora tricolor
47Aurora from space iss
48Comet NEAT kinky tail
49Long Term Solar Evolution
- As the sun ages, its core collapses as hydrogen
converts to helium, and this increases the
gravity and pressure and fusion rate in the core - So, the sun is getting more luminous on the long
term - During the 4.56 billion year life of the solar
system, the sun has increased in luminosity by
about 25. - This will continue, and gradually accelerate
50Long term L,R,T