Our Star the Sun

The Sun – Our Star Our 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 Sun The 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 fusion Nuclear 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

Granules

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 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