Our Star the Sun

The Sun – Our StarOur sun is considered an “average” star and is one of the 200 BILLION stars that make up the Milky Way galaxy. But by no means does that make our star insignificant! Everything – from the foods we eat to the fossil fuels we burn – starts with solar energy.

General properties of our sun

• Average-sized star• 109 times Earth’s diameter• 333,000 times Earth’s mass• Composed of gas

Ultra-violet image

Structure of the SunThe sun has 4 main layers (because the sun is made of gas, these layers are not sharply defined):•Solar interior•Photosphere (visible surface)•Chromosphere (atmospheric layer)•Corona (atmospheric layer)

Solar Interior

Layers of the Solar Atmosphere

Visible

Photosphere

X-ray

Chromosphere

Coronal activity, seen in visible

light

Corona

Sun Spot Regions

Solar interior• The sun’s energy comes from

nuclear fusion, which takes place inside the sun’s core under intense pressure and heat

• Nuclear fusion is a reaction in which hydrogen atoms smash together to form helium, releasing a tremendous amount of energy

• Core temp = 27 million°F

Nuclear fusionNuclear Fusion Creating New Elements

Photosphere• Photo = sphere = • The photosphere is the sun’s thin

surface • We see it as a yellow ball• Surface temp = 10,000°F• Sunspots and granules are located here!

10 Day Solar Animation

Sun Spots

• Cooler regions of the photosphere (T ≈ 7,000°F)

• Only appear dark against the bright sun

• Would still be brighter than the full moon

• Created by the sun’s magnetic field• Originally discovered by Galileo in 1610

– We know the sun’s rotation is 27 days by observing the movement of the sunspots!

Visible X-ray

Sunspots

Sun Spots

Energy Transport in the Photosphere

Bubbles of hot gas rising up

Cool gas sinking down

≈ 1000 km

Bubbles last for ≈ 10 – 20 min.

• Energy created in the core moves out to the surface, where it “boils” in giant cells of circulating heat called granules

GranulesGranules

Chromosphere• Chromo = sphere = • The first layer of the solar atmosphere,

directly above the photosphere• Can’t normally see it because of

brightness of photosphere• Temperature is about 36,000°F• Contains spicules, prominences, and

solar flares

photosphere

chromosphere

Solar Activity, seen in soft X-rays

• Narrow jets of exploding gases, thousands of miles high

Spicules

• Giant clouds of gas ejected from the chromosphere• Trapped by magnetic fields – often looks like a loop

Prominences

YouTube: Prominence

Solar Flares Solar flare: an

explosion on the surface of the sun above a sunspot

Releases enormous amounts of energy, much of it as ultraviolet, radio, and X-ray radiation

This intensifies solar storms

YouTube: Solar Flares

Corona• Corona (Latin/Spanish) = • The outer layer of the solar atmosphere

– Can only see it during solar eclipse• Temp = 1.8 million °F• Solar winds stream out from here

– We are mostly protected from solar winds by Earth’s magnetic field!

Solar winds•Streams of charged particles

(plasma) escaping from the sun•Can affect us on Earth!

– e.g., power outages, disruption of navigation systems and satellites (YES! your cell phone!), radiation exposure to astronauts

– Coronal mass ejections are huge bursts of solar wind

Coronal Mass Ejection

Aurora borealis• Aurora = borealis = • Also called the northern lights, auroras

are bright displays of light caused by solar winds interacting with the upper atmosphere near Earth’s poles.– The poles are where the magnetic fields

are weaker, allowing the particles in• Solar flares intensify auroras

Secrets of a Dynamic Sun

YouTube: From Space Station YouTube:

Over Norway

The Telegraph: Solar phenomena in pictures

Life cycle of the sun

• A star the size of the sun can exist in its present stable state for 10 billion years.

• As the sun is already 4.5 billion years old, it is “middle-aged.”

Star size comparison

video

Your summary• Discuss with your table partner about what

you will write in your summary box– Should be 1-3 sentences giving the major points

of the Sun notes