The Sun – Our Star

Our sun is considered an “average” star and is one of the 100 BILLION stars that make up the Milky Way galaxy. But by no MEANS does that make our star insignificant! Everything - from the fossil fuels we burn to the foods we eat – is ultimately derived from solar energy.

General Properties

• Average sized star

• Central temperature = 15 million 0K (27 million 0F)

• 333,000 times Earth’s mass

• 109 times Earth’s diameter

• Consists entirely of gas (density = 1.4 g/cm3; compared to Earth at 5.5 g/cm3)

• Surface temperature = 5800 0K (10000 0F)

Ultra-violet image

Structure of the Sun Because the sun is made of gas, no sharp

boundaries exist between its various layers. Keeping this in mind, we can divide the sun into four parts:

solar interior

photosphere (the 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: Nuclear Fusion

• During nuclear fusion, energy is released because some matter is actually converted to energy.

• Nuclear fusion is the way that the sun produces energy. This reaction smashes hydrogen atoms together to form helium, releasing a tremendous amount of energy.

Nuclear FusionNuclear Fusion Creating New Elements

• Region of the sun that radiates energy into space. This is the part we see!

The Photosphere

• Depth ≈ 500 km• Temperature ≈ 5800 oK (10,000 oF)

10 Day Solar Animation

Energy Transport in the Photosphere•Energy generated in the sun’s center must be transported outward. In the photosphere, this happens through Convection.

•This convection creates a grainy texture called granules that are the size of Texas!

Bubbles of hot gas rising up

Cool gas sinking down

≈ 1000 km

Bubbles last for ≈ 10 – 20 min.

Granulation

… is the visible consequence of convection

Granules

Sun Spots

Cooler regions of the photosphere (T ≈ 4240 K).

Only appear dark against the bright sun. Would still be

brighter than the full moon when placed on the night sky!

Sun Spots-occur in the photosphere; were originally discovered by Galileo in 1610-we know the sun’s rotation is 27 days by observing the movement of the sunspots! -they are created by the Sun’s magnetic field

Visible X-ray

Sunspots

• The chromosphere is the next layer of the solar atmosphere found directly above the photosphere.

• Temperature is about 20,000 °C (36,000 °F)

• This burning gas is a few thousand kilometers thick.

• Its top contains numerous spicules, which are narrow jets of rising material. They are typically thousands of kilometers high with a 10,000 kilometer maximum height and last 5-15 min.

Chromosphere

photosphere

chromosphere

Solar Activity, seen in soft X-rays

Prominences

• Prominences are trapped by magnetic fields that extend from regions of intense solar activity.

• Prominences are huge cloudlike structures consisting of gases from the chromosphere.

Solar Flares

Solar flares are tremendous explosions on the surface of the sun. They normally last about an hour and appear as a sudden brightening of the region above a sunspot.

Solar flares release enormous amounts of energy, much of it in the form of ultraviolet, radio, and X-ray radiation.

This intensifies solar wind

YouTube: Solar Flares

Corona

• The corona is the outer, weak layer of the solar atmosphere.

• The temperature at the top of the corona exceeds 1 million °C (1.8 million °F), which makes it the hottest layer.

• The streams of protons and electrons that boil from the corona make up the Solar wind.

Coronal Mass Ejection

Aurora Borealis

Auroras are bright displays of light caused by solar radiation interacting with the upper atmosphere near Earth’s poles.

Solar flares can intensify the auroras.

Youtube: Secrets of a

Dynamic Sun

YouTube: From Space Station

YouTube:Over Norway

The Sun’s Magnetic Dynamo

This differential rotation might be responsible for magnetic activity of the sun.

The sun rotates faster at the equator than near the poles. Why? …because it’s a huge ball of gas!!!

Life Cycle of the Sun

• It is thought that 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.”

Death of a Star

Star size comparison

video