SunspotsSunspots

Sometimes Very StrikingSometimes Very Striking

……Sometimes NotSometimes Not

Obvious Question:Obvious Question:

Why are sunspots dark?Why are sunspots dark?

Answer: they are simply Answer: they are simply coolercooler than the than the surrounding regions, so give off less surrounding regions, so give off less light – they thus look dark by contrast. light – they thus look dark by contrast.

But , if cooler, how do they withstand the But , if cooler, how do they withstand the extra pressure exerted by the extra pressure exerted by the surrounding hotter gases? Why don’t surrounding hotter gases? Why don’t sunspot regions collapse?sunspot regions collapse?

Second IssueSecond Issue

Why do they come and go? Does that Why do they come and go? Does that behaviour exhibit any regularity, or is behaviour exhibit any regularity, or is it a random process?it a random process?

To Answer Those QuestionsTo Answer Those Questions

Observe the sunspots over Observe the sunspots over many many centuriescenturies – determine their motions, – determine their motions, numbers, distribution on the face of numbers, distribution on the face of the sun, longevity, etc.the sun, longevity, etc.

But some But some new physical toolsnew physical tools (~1920s) turn out to be critical in (~1920s) turn out to be critical in providing the eventual answer as to providing the eventual answer as to their naturetheir nature

Sunspot MotionSunspot Motionhttp://science.nasa.gov/ssl/pad/solar/images/sunturn.gifhttp://science.nasa.gov/ssl/pad/solar/images/sunturn.gif

Large Complexes Can Be Large Complexes Can Be SeenSeen

In DetailIn Detail

The The GlobalGlobal Behaviour: Behaviour: They Come and Go!They Come and Go!

Consider Chicken Pox:Consider Chicken Pox:do the individual spots move do the individual spots move

about?about?

NoNo

Chickenpox is a viral infection that Chickenpox is a viral infection that causes a red, itchy rash on the skin. causes a red, itchy rash on the skin.

The chickenpox rash usually The chickenpox rash usually appears appears first on the abdomen or back and first on the abdomen or back and face, and then spreads to almost face, and then spreads to almost everywhere else on the body, everywhere else on the body, including the scalp, mouth, nose, including the scalp, mouth, nose, ears, and genitals. ears, and genitals.

Likewise the Sunspots Likewise the Sunspots

They form in a given location, at a They form in a given location, at a middling latitude, and persist for a middling latitude, and persist for a while (carried along by the sun’s while (carried along by the sun’s rotation) before fading away.rotation) before fading away.

New spots form later, but tend to be New spots form later, but tend to be closer to the equatorcloser to the equator – as though the – as though the ‘infection’ spreads to new areas.‘infection’ spreads to new areas.

Hence the ‘Butterfly Hence the ‘Butterfly Diagram’Diagram’

The Physical Explanation: The Physical Explanation: Magnetic Fields Provide Magnetic Fields Provide

PressurePressure

Magnetic Field LoopsMagnetic Field Loops

Charged Particles in Magnetic Charged Particles in Magnetic FieldsFields

Magnetic Fields and Magnetic Fields and TelevisionTelevision

……or in the Earth’s Magnetic or in the Earth’s Magnetic FieldField

Aurora BorealisAurora Borealisvisit visit

http://www.geo.mtu.edu/weather/aurora/images/aurora/jan.curtishttp://www.geo.mtu.edu/weather/aurora/images/aurora/jan.curtis

But Why Does the But Why Does the Sunspot Pattern Vanish?Sunspot Pattern Vanish?

Remember the 11-year periodicity in Remember the 11-year periodicity in the total numbers of sunspots. There the total numbers of sunspots. There are periodic ‘recoveries’ from the are periodic ‘recoveries’ from the ‘infection.’‘infection.’

Why??Why??

Astrophysical Observation Reveals Astrophysical Observation Reveals Periodic ReversalsPeriodic Reversals of Magnetic of Magnetic

FieldsFields

This happens on both Sun and Earth!This happens on both Sun and Earth!

On the Sun:On the Sun: every ~11 years, quite reliable every ~11 years, quite reliable

On the Earth:On the Earth: timescale of hundreds of timescale of hundreds of thousands of years; considerable thousands of years; considerable randomness.randomness.

[The evidence is in magnetic ores and rocks.][The evidence is in magnetic ores and rocks.]

(Does the latter have any effect? Perhaps an (Does the latter have any effect? Perhaps an influence on mutation rates, via cosmic rays)influence on mutation rates, via cosmic rays)

A Familiar Horseshoe A Familiar Horseshoe MagnetMagnet

A ‘Bar’ MagnetA ‘Bar’ Magnet

Sun’s Magnetic Field – like a Sun’s Magnetic Field – like a ‘Bar’‘Bar’

Gets Too Convoluted!Gets Too Convoluted!

What is Happening?What is Happening?

The magnetic field gets tangled, thanks to The magnetic field gets tangled, thanks to the differential rotation of the sun. It the differential rotation of the sun. It becomes ‘easier’ to simply dump the old becomes ‘easier’ to simply dump the old chaotic field and set up a new one – the chaotic field and set up a new one – the other way around! (So it’s actually a 22-other way around! (So it’s actually a 22-year cycle.)year cycle.)

[Sidebar: Compare this to ‘magnetic [Sidebar: Compare this to ‘magnetic reconnection’]reconnection’]

Analogy: Consider a SpringAnalogy: Consider a Spring

……a really stiff onea really stiff one

Put Jack Back in the BoxPut Jack Back in the Box

About My Analogies…About My Analogies…

The Earth-Sun ConnectionThe Earth-Sun Connection

Does the varying magnetic field/sunspot Does the varying magnetic field/sunspot number on the face of the sun affect the number on the face of the sun affect the Earth in any way? For example:Earth in any way? For example:

Does the sun get a little dimmer because Does the sun get a little dimmer because of the sunspots? [Answer: possibly a little]of the sunspots? [Answer: possibly a little]

If so, is it enough to matter? [Answer: If so, is it enough to matter? [Answer: almost certainly not, for climate, crops, almost certainly not, for climate, crops, etc.]etc.]

What About Other What About Other Connections?Connections?

Sunspots come and go every 11 years. What else? Sunspots come and go every 11 years. What else?

Stock markets? Stock markets? Women’s fashions? Women’s fashions? Voting trends?Voting trends? Serious flu epidemics?Serious flu epidemics? Stanley Cups for the Montreal Canadiens?Stanley Cups for the Montreal Canadiens?

But these oscillations may be utterly independent, But these oscillations may be utterly independent, with no cause-and-effect relationship at all. with no cause-and-effect relationship at all. (There is no good evidence in support of a solar (There is no good evidence in support of a solar influence in influence in any any of these!)of these!)

How About How About LongerLonger Timescales?Timescales?

The historical record shows that The historical record shows that sunspot activity waxes and wanes on sunspot activity waxes and wanes on longer timescaleslonger timescales as well. as well.

Does this have any effect on the Does this have any effect on the Earth? Earth?

Example: The Maunder Example: The Maunder MinimumMinimum

Climatological Climatological Effects?Effects?