THE SUN

The Sun

• The sun has a diameter of 900,000 miles (>100 Earths could fit across it)

• >1 million Earths could fit inside it.

• The sun is composed of about 75% Hydrogen and 24% Helium.

• The sun makes up 99.8% of the solar system’s mass.

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Nuclear FusionThe process of combining nuclei of small atoms to form more-massive nuclei.

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Sun Structure

The Core

•The center of the sun.

•15,000,000oC

•Nuclear fusion occurs here at a rate of 600 million tons of hydrogen into helium per second.

The Radiative Zone

•The zone surrounding the core.

•The energy created in the core moves through this zone by electromagnetic waves, or radiation.

The Convective Zone

•The area surrounding the radiative zone.

•Energy moves through this zone by convection (hot gases carry energy to the surface where the gases lose energy and cool. They then sink back down where they are warmed again by the radiative zone).

What is convection?

The Photosphere

•The innermost layer of the solar atmosphere.

•This is the layer of visible light that we see.

The Chromosphere

•The layer above the photosphere.

•This layer is sometimes called the color sphere as it glows with a reddish color that we can see during eclipses.

The Corona•The outermost layer of the sun’s atmosphere.

•This layer is thin and only seen during eclipses.

Solar Activity

• The sun rotates on average once every 27 days. • Movements of gases within the sun’s convective

zone and the movements caused by the sun’s rotation produce magnetic fields.

• Magnetic fields cause convection to decrease in spots which causes cooler regions on the photosphere to appear called sun spots.

What causes sunspots?

Sunspots

• A dark area of the photosphere of the sun that is cooler than the surrounding areas and that has a strong magnetic field

The Sunspot Cycle

• Observations of sunspots showed astronomers that the sun rotates.

• The number and positions of sunspots vary in a cycle that lasts about 11 years.

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The Sunspot Cycle

• Begins when the # of sunspots is very low but begins to increase

• # increases until it reaches peak of 100 or more

• # decreases until it reaches a minimum and the cycle starts over

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The sunspot cycle affects most other solar activities

because of the changing solar magnetic field.

Prominences

• Great clouds of glowing gases that form arches that reach high above the sun’s surface.

Solar Flares

• An explosive release of energy that comes from the sun and that is associated with magnetic disturbances on the sun’s surface.

• Most violent of all solar disturbances

• Electrically charged particles are released from the sun.

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Solar Flares

• Solar flares release the energy stored in the strong magnetic fields of sunspots

• Solar flares accompany increases in sunspot activity.

Solar Flare

Solar Flare

Coronal Mass Ejection

• Parts of the corona that are thrown off the sun.

Solar Winds

• Solar wind is electrons and electrically charged particles (ions) which flow outward from the sun to the rest of the solar system

What are solar winds?

How do events on the sun affect everyday human activities?

• As emissions from the sun encounter Earth, they can ignite geomagnetic storms. These geomagnetic storms can cause electrical power outages, damage communication satellites, and affect radio communications.

• Increased solar emissions can also lead to a higher frequency of auroras

Auroras

• Colored light produced by charged particles from the solar wind and from the magnetosphere that react with and excite the oxygen and nitrogen of Earth’s upper atmosphere; usually seen in the sky near Earth’s magnetic poles.

• Turn off the lights and enjoy the Auroras!