THE SUNTHE SUN

Energy from the sun, in the form of Energy from the sun, in the form of sunlight supports all life via sunlight supports all life via photosynthesis, and drives the photosynthesis, and drives the Earth’s climate and weather.Earth’s climate and weather.

THE SUNTHE SUNBegan shining 5 billion years Began shining 5 billion years agoagoExpected to continue shining Expected to continue shining for 5 billion years morefor 5 billion years moreAt the end of its life it will At the end of its life it will start to fuse helium into start to fuse helium into heavier elements becoming a heavier elements becoming a red giant and engulfing the red giant and engulfing the Earth.Earth.73% hydrogen73% hydrogen25% helium25% heliumTiny fraction is other elements Tiny fraction is other elements such as C, N, O, Ni, Fe etc.such as C, N, O, Ni, Fe etc.Over 100 x diameter of the Over 100 x diameter of the earthearth

A close look at the SunA close look at the SunThe sun is made of The sun is made of many layersmany layers– CoreCore– Radiative and Radiative and

convective Zoneconvective Zone– PhotospherePhotosphere– ChromosphereChromosphere– CoronaCorona

The CoreThe Core

Where nuclear fusion occurs (light Where nuclear fusion occurs (light atoms fuse to become heavier ones)atoms fuse to become heavier ones)

Temperatures and pressures are Temperatures and pressures are enormousenormous

Temperatures reach 15 million Temperatures reach 15 million oo C. C.

Radiative and Convective ZoneRadiative and Convective ZoneRadiativeRadiative– The plasma is very The plasma is very

densedense– Light takes Light takes

approximately 100,000 approximately 100,000 years to pass through years to pass through as it is constantly as it is constantly absorbed and re-absorbed and re-emittedemitted

ConvectiveConvective– Bubbles of hot plasma Bubbles of hot plasma

circulate up toward the circulate up toward the surface while cooler surface while cooler regions of plasma sinkregions of plasma sink

The PhotosphereThe Photosphere

Surface of the Sun made Surface of the Sun made

of churning gasesof churning gases

Lowest temperatures of all of the Lowest temperatures of all of the layers (5500layers (5500oo C) C)

The Sun’s yellow colour originates in The Sun’s yellow colour originates in the photosphere. We see this the photosphere. We see this because it is brighter than the because it is brighter than the chromosphere.chromosphere.

The ChromosphereThe Chromosphere

Is a thin layer of atmosphere above Is a thin layer of atmosphere above the photosphere (hotter than the the photosphere (hotter than the photosphere)photosphere)

Has a red colour to it which we can Has a red colour to it which we can only see during a total solar eclipse.only see during a total solar eclipse.

Extends beyond the chromosphere for Extends beyond the chromosphere for millions of kilometersmillions of kilometers

Again most clearly visible during a solar Again most clearly visible during a solar eclipseeclipseThe corona is hotter than the photosphere The corona is hotter than the photosphere because the gases are ionized.because the gases are ionized.

The CoronaThe Corona

Magnetic FieldsMagnetic Fields

Earth has its own magnetic field Earth has its own magnetic field (caused by spinning molten metal (caused by spinning molten metal deep in the Earth’s core)deep in the Earth’s core)

The Sun has a magnetic field The Sun has a magnetic field generated by the movement of generated by the movement of plasma deep in the Sun’s interior.plasma deep in the Sun’s interior.

SunspotsSunspotsOccur in the Occur in the photospherephotosphere

Indicate areas Indicate areas where the magnetic where the magnetic field is strong which field is strong which prevents the prevents the plasma from mixing plasma from mixing thus allowing it to thus allowing it to cool to form the cool to form the darker spotsdarker spots

ProminenceProminenceBright streams of Bright streams of plasma extending plasma extending from the photosphere from the photosphere into the coronainto the corona

The plasma is The plasma is electrically charged electrically charged and can be shaped by and can be shaped by the magnetic field of the magnetic field of the Sunthe Sun

Can last for days or Can last for days or weeksweeks

Solar flaresSolar flaresMost solar flares occur Most solar flares occur near sunspots (thought to near sunspots (thought to be a result of magnetic be a result of magnetic fields)fields)Occur in the chromosphere Occur in the chromosphere and the coronaand the coronaIt is a huge outbreak of It is a huge outbreak of electrified particles that electrified particles that are thrown into space at a are thrown into space at a speed of 1000 km/s. (spits speed of 1000 km/s. (spits out particles so fast that out particles so fast that they cannot be trapped by they cannot be trapped by the Sun’s gravity.)the Sun’s gravity.)If directed at the Earth, If directed at the Earth, they are diverted from the they are diverted from the surface towards the poles.surface towards the poles.

Coronal Mass EjectionCoronal Mass EjectionAn extremely powerful kind of flare.An extremely powerful kind of flare.

If directed at the Earth it can damage If directed at the Earth it can damage satellites. Astronauts on shuttles and satellites. Astronauts on shuttles and the space station must go to areas the space station must go to areas which offer more protection from the which offer more protection from the cosmic radiationcosmic radiation

They are diverted from the Earth’s They are diverted from the Earth’s surface by our magnetic field towards surface by our magnetic field towards the poles. This can create auroras.the poles. This can create auroras.

When these charged particles hit the When these charged particles hit the earth's atmosphere, they excite the earth's atmosphere, they excite the atoms contained in the atmosphere. atoms contained in the atmosphere. These excited atoms have a higher These excited atoms have a higher energy state than usual and so want energy state than usual and so want to get back to a more normal energy to get back to a more normal energy state. The excited atoms give off state. The excited atoms give off excess energy in the form of heat, or excess energy in the form of heat, or in the case of the aurora borealis, in the case of the aurora borealis, light. light.

Aurora BorealisAurora Borealis

Occur at the polesOccur at the poles

Aurora borealisAurora borealis

Solar WindSolar Wind

Steady stream of charged particles Steady stream of charged particles from the Sun’s surface in all from the Sun’s surface in all directionsdirections