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Solar Thermostat

Decline in core temperature causes fusion rate to drop, so core contracts and heats up.

Rise in core temperature causes fusion rate to rise, so core expands and cools down.

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Clicker Question

What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy?

A. The core would expand and heat up slightly.B. The core would expand and cool.C. The Sun would blow up like a hydrogen bomb.

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Clicker Question

What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy?

A. The core would expand and heat up slightly.B. The core would expand and cool.C. The Sun would blow up like a hydrogen bomb.

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Energy gradually leaks out of radiation zone in form of randomly bouncing photons.

How does the energy from fusion get out of the Sun?

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Convection takes energy to surface. Bright blobs on photosphere show where hot gas is reaching the surface.

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• Patterns of vibration on the surface tell us about what is happening inside the Sun. This research is called

helioseismology. Large-scale change in color from left to right reflects the sun’s rotation.

How we know what is happening inside the Sun?

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What causes solar activity?

Sunspots, solar flares, and prominences cause solar activity. They are all related to magnetic fields.

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Sunspots

Temperature is 4000 K and they are cooler than other parts of the Sun’s surface.

They also have strong magnetic fields.

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Zeeman Effect

We can measure magnetic fields in sunspots by observing the splitting of spectral lines.

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Prominences often connect sunspot pairs.

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Magnetic activity causes solar flares that send bursts of X rays and charged particles into space This X-ray photo is from TRACE.

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Magnetic activity also causes solar prominences that erupt high above the Sun’s surface. Height is 20X Earth’s diameter!

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The corona appears bright in X-ray photos, indicating its high temperature.

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Coronal mass ejections send bursts of energetic charged particles out through the solar system.

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The number of sunspots rises and falls in an 11-year cycle.

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