The Sun’s Surface; Sunspots

An Impressive Body

The Corona

Various Kinds of Activity

Solar Flares and Prominences

Coronal Mass Ejectionshttps://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.

PuzzleIf 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 QuestionWhy do they come and go? Does that

behaviour exhibit any regularity, or is it a random process?

To Answer Those Questions 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 Motionhttps://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?

NoChickenpox 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

FieldsThis 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 ConnectionDoes the varying magnetic field/sunspot

number affect the Earth in any way? For example:

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?

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?