The Sun’s Surface;
Sunspots
An Impressive Body
The Corona
Various Kinds of Activity
Solar Flares and Prominences
Coronal Mass Ejections
https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=11095
They Can Directly Affect Us!
The Surface in Detail:
Granulation due to
Convection
The Interior in Cross-Section
Sunspots
Sometimes Very Striking
…Sometimes Not
Obvious Question:
Why are sunspots dark?
Answer: they are simply cooler (by 1000-1500
degrees) than the surrounding regions, so
give off less light – they thus look dark by
contrast.
The material is still quite hot! If you took the
sunspot region out of the Sun, you would see
that it gives off lots of light.
Puzzle
If sunspot regions are cooler, how do they
withstand the extra pressure exerted by the
surrounding hotter gases?
Why don’t sunspot regions collapse and vanish?
Second Question
Why do they come and go? Does that
behaviour exhibit any regularity, or is it a
random process?
To Answer Those Questions
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Observe the sunspots over many centuries
– determine their motions, numbers,
distribution on the face of the sun,
longevity, etc.
But some new physical tools (~1920s)
turn out to be critical in providing the
eventual answer as to their nature
Sunspot Motion
https://www.youtube.com/watch?v=oInoNnPsxcA
Large Complexes Can Be Seen
huge sunspot moving as sun rotates
We Can Study Them in Detail
The Global Behaviour:
They Come and Go!
Consider Chicken Pox:
do the individual spots move a lot?
- say, from chest to arms?
No
Chickenpox is a viral infection that causes a
red, itchy rash on the skin.
The chickenpox rash usually appears first on
the abdomen or back and face, and then
spreads to almost everywhere else on the
body, including the scalp, mouth, nose,
ears, and genitals.
Likewise the Sunspots
They form in a given location, at a middling latitude,
and persist for a while (carried along by the sun’s
rotation, of course) before fading away.
[Note: Individual sunspots do ‘drift around’ a little, relative to
one another; this is one way we know the Sun’s surface is
fluid, not solid. But those changes in position are modest.]
New spots form later, but tend to be closer to the
equator – as though the ‘infection’ spreads to
new areas.
Hence the
‘Butterfly Diagram’
Magnetic ‘Field Lines’
indicating the presence and strength
of a magnetic field
Consider a Boy-Scout Compass
Magnetic Field Loops
How Do We Detect These Fields?
Not Using Compasses!
Answer: We study subtle features in the absorption lines in
the spectrum of the Sun. Magnetic fields affect atoms!
How Do Charged Particles
Move in Magnetic Fields?
We Can Steer Electrons:
Magnetic Fields in TV Sets
A magnet steering a beam of electrons
The Earth’s Magnetic Field
Aurora Borealis
But Why Does the
Sunspot Pattern Vanish?
Remember the 11-year periodicity in the
total numbers of sunspots. There are
periodic ‘recoveries’ from the ‘infection.’
Why??
Astrophysical Observations Reveal
Periodic Reversals of Magnetic Fields
This happens on both Sun and Earth!
On the Sun: every ~11 years, quite reliable
On the Earth: timescale of hundreds of
thousands of years, but with considerable
randomness. [The evidence is in magnetic ores
and rocks.]
Does the latter have any effect? Perhaps an influence on
biological mutation rates, since the Earth’s surface will
be more bombarded by cosmic rays.
Two Kinds of Simple Magnets
Horseshoe
Bar
Sun’s Magnetic Field – like a ‘Bar’
It Gets Tangled Up!
Animation of the tangling of the solar magnetic field
What is Happening?
The magnetic field gets tangled because of the
differential rotation of the sun. It becomes
‘easier’ to simply dump the old chaotic field and
set up a new one.
When it does so, the new field is ‘the other way
around!’ (N and S poles have swapped.) So it’s
actually a 22-year cycle, not 11-year.
A (Helpful?) Analogy:
Consider a Spring
…a really stiff one
Put Jack Back in the Box
About My Analogies…
The Earth-Sun Connection
Does the varying magnetic field/sunspot number
affect the Earth in any way? For example:
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Does the sun get a little dimmer because of the
sunspots? They are dark regions: is less total
light given off? [Answer: probably not!]
If so, is it enough to matter? [Answer: almost
certainly not, for climate, crops, etc.]
What About Other Connections?
Sunspots come and go every 11 years. What else varies
like that?
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Stock markets?
Women’s fashions?
Voting trends? (Conservative v Liberal, say)
Serious flu epidemics?
Stanley Cups for the Montreal Canadiens?
http://journal.borderlands.com/2000/sunspots-and-human-behavior/
There is no compelling evidence for any such connections!
How About Longer Timescales?
The historical record shows that sunspot
activity waxes and wanes much more
dramatically on longer timescales as well.
Does this have any effect on the Earth?
One obvious manifestation might be on
climate.
The ‘Maunder Minimum’
Climatological
Effects?