CHAPTER 10:CHAPTER 10:The Sun: Our Extraordinary Ordinary Star

What do you know about the What do you know about the Sun?Sun?

Brightest object in our Solar systemBrightest object in our Solar system Center of our S.S.Center of our S.S. HotHot Large (largest object in the solar system)Large (largest object in the solar system) StarStar Can cause blindnessCan cause blindness Fusion at the coreFusion at the core Plasma statePlasma state Solar WindSolar Wind Has been worshipped as RaHas been worshipped as Ra Gives us lightGives us light Planets orbit the SunPlanets orbit the Sun LayeredLayered RotateRotate Average sized starAverage sized star 5 by old, 5 by left5 by old, 5 by left

THE SUNTHE SUN

Overview Overview The Sun is a huge ball of hot gasThe Sun is a huge ball of hot gas

Primary component is hydrogenPrimary component is hydrogen Secondary component is heliumSecondary component is helium tiny amounts of other elements are recognized by spectral tiny amounts of other elements are recognized by spectral

analysis of surface gasesanalysis of surface gases Size Size

100 Earths across in diameter100 Earths across in diameter one million Earths would fit insideone million Earths would fit inside Contains 99.85% of the mass in the solar systemContains 99.85% of the mass in the solar system If the Sun was as close to the Earth as the Moon, it would If the Sun was as close to the Earth as the Moon, it would

consume 2/3 of the sky.consume 2/3 of the sky. AgeAge

Estimated at 5 billion years oldEstimated at 5 billion years old It will be another 5 billion years until it begins to dieIt will be another 5 billion years until it begins to die

BIRTHBIRTH

Rotating nebular dusts and gases condense and Rotating nebular dusts and gases condense and flatten, producing a protoplanetary disk and flatten, producing a protoplanetary disk and protosun at the center.protosun at the center.

Temperature of the protosun continues to rise as Temperature of the protosun continues to rise as more matter collapses inward.more matter collapses inward.

If the temperature at the core of the protosun If the temperature at the core of the protosun rises above 10 million Kelvin, then fusion of rises above 10 million Kelvin, then fusion of hydrogen into helium nuclei occurs.hydrogen into helium nuclei occurs.

The Sun becomes a star at this time.The Sun becomes a star at this time.

ANATOMY OF THE SUNANATOMY OF THE SUN

Internal Structure--The Sun has three Internal Structure--The Sun has three internal layersinternal layers

Deep, dense, hot core (+ 10 million Kelvin)Deep, dense, hot core (+ 10 million Kelvin) A radiative zoneA radiative zone A convective zoneA convective zone

THE SOLAR THE SOLAR INTERIORINTERIOR

Internal StructureInternal Structure

Thermonuclear Core (25 % of radius)Thermonuclear Core (25 % of radius)Radiative zone (55 % of radius)Radiative zone (55 % of radius)Convective zone (20% of radius)Convective zone (20% of radius)Photons created in the core take 170,000 Photons created in the core take 170,000

years to make the journey through the years to make the journey through the radiative zone.radiative zone.

Hot gas rises and falls in the convective Hot gas rises and falls in the convective zone, eventually reaching the surface of zone, eventually reaching the surface of the Sun.the Sun.

The CoreThe Core

Fusion at the coreFusion at the core The crushing, immense weight of the outer The crushing, immense weight of the outer

layers compresses the gas and increases its layers compresses the gas and increases its temperaturetemperature

When the temperature reaches 10 million When the temperature reaches 10 million Kelvin, fusion of hydrogen into helium Kelvin, fusion of hydrogen into helium beginsbegins

Fusion of hydrogen into helium releases Fusion of hydrogen into helium releases energy at the expense of massenergy at the expense of mass

The Sun is powered by thermonuclear fusion, The Sun is powered by thermonuclear fusion, which converts hydrogen into helium.which converts hydrogen into helium.

Radiative ZoneRadiative Zone

It takes about 170,000 years for the energy It takes about 170,000 years for the energy released from the core to travel through the released from the core to travel through the radiative layer.radiative layer.

Photons created at the core carry the energy Photons created at the core carry the energy through this layerthrough this layer

Convective ZoneConvective Zone

This energy heats up the gases in the this This energy heats up the gases in the this zone and delivers its energy to the Sunzone and delivers its energy to the Sun’’s s surface by convection (hot, less dense gases surface by convection (hot, less dense gases rise and cooler, more dense gases sink)rise and cooler, more dense gases sink)

Why does the Sun stay a Why does the Sun stay a constant size?constant size?

Outward pressure due to hydrogen fusion Outward pressure due to hydrogen fusion is balanced by the inward pressure of the is balanced by the inward pressure of the overlying gases (hydrostatic equilibrium).overlying gases (hydrostatic equilibrium).

The Sun’s interior is held stable by a balance between pressure forces and gravity, in a condition called hydrostatic equilibrium.

Outer layers of the SunOuter layers of the Sun

Photosphere (5800 K, low density, 0.01% Photosphere (5800 K, low density, 0.01% of air at sea level)of air at sea level)

Chromosphere (4000 K – 10,000 K, less Chromosphere (4000 K – 10,000 K, less dense than photosphere)dense than photosphere)

Corona (1 million K, extremely low densityCorona (1 million K, extremely low density—10 trillion times less than air at sea —10 trillion times less than air at sea level)level)

PhotospherePhotosphere

Light energy (mostly in the form of visible light, Light energy (mostly in the form of visible light, and a smaller percentages of UV rays and and a smaller percentages of UV rays and infrared light, x-rays, gamma rays, microwaves infrared light, x-rays, gamma rays, microwaves and radio waves) is released from the Sunand radio waves) is released from the Sun’’s s surface, which is 5800 Kelvin in temperature.surface, which is 5800 Kelvin in temperature.

The density of the photosphere (SunThe density of the photosphere (Sun’’s surface) is s surface) is 0.01% of the air that we breathe.0.01% of the air that we breathe.

Granulated surface represents the rising and Granulated surface represents the rising and falling hot gasesfalling hot gases

Darker areas represent cooler temperaturesDarker areas represent cooler temperatures

The bright visible surface of the Sun is The bright visible surface of the Sun is called the photosphere. called the photosphere.

When looking at the Sun, the edges appear orange and darker than the central yellow region. This is known as limb darkening.

Upon closer inspection, the Sun has a marbled pattern called granulation, caused by the convection of gases just beneath the photosphere.

During an eclipse, sometimes you can see the layers of the Sun’s atmosphere just above the photosphere, which emits only certain wavelengths of light, resulting in a reddish appearance. We call this the sphere of color, or chromosphere.

The solar chromosphere is characterized by jets of gas extending upward called spicules.

CoronaCorona Hot, ionized extremely thin gas up to 1 million Hot, ionized extremely thin gas up to 1 million

KK caused by the Suncaused by the Sun’’s complex magnetic fieldss complex magnetic fields charged particles are moving so fast that they charged particles are moving so fast that they

can escape the gravitational pull of the Sun. can escape the gravitational pull of the Sun. This is the solar wind.This is the solar wind.

Sun ejects about a million tons of matter per Sun ejects about a million tons of matter per secondsecond

matter travels fast (2.9 x 10matter travels fast (2.9 x 1066 km/h) km/h) 5 particles per cc by time it reaches the Earth 5 particles per cc by time it reaches the Earth

(atm 6 x 10(atm 6 x 101919 particles per cc) particles per cc)

THE SOLAR CORONATHE SOLAR CORONA

Seen in visible light during an eclipse.

This x-ray image shows the million-degree gases.

Bright areas are where the Sun’s magnetic field is so strong that it trap the super heated gases of the Corona. Darker areas represent coronal holes. This is where the solar wind originates (700 km/s).

The temperature of the solar gases increase with distance from the solar surface.

Within the narrow transition region between the chromosphere and the corona, the temperature increases by 100 times.

Surface Features of the SunSurface Features of the Sun

SunspotsSunspotsPlagesPlagesFilament (a top view of a prominence)Filament (a top view of a prominence)ProminencesProminencesSolar FlaresSolar FlaresCoronal Mass EjectionsCoronal Mass EjectionsAll are due to changes in solar magnetic All are due to changes in solar magnetic

fieldsfields

Sunspots are regions of intense magnetic fieldsSunspots are regions of intense magnetic fields

For sunspots to form, the magnetic field lines of the Sun become intertwined after several rotations, creating regions of intense magnetic fields. Sunspots are produced at distortions along these field lines.

Coronal loop of hot electrified gas can be 300,000 miles high and span 30 Earths.

It takes the Sun 25 days to rotate at its equator, and 35 days to rotate at its poles. Its rotational speed is roughly 2 km/s.

Sunspots have two regions: the inner, darker umbra and the outer penumbra.

Overlapping sunspots

SunspotsSunspots

Darker regions of the Sun are cooler than the brighter yellow regions.

The number of sunspots on the photosphere varies The number of sunspots on the photosphere varies over an eleven-year cycle. over an eleven-year cycle.

Sunspot Maximum Sunspot Minimum

Sunspot max to min to max = 22 years

SunspotsSunspots

Sunspot cycle is 11 years from sunspot Sunspot cycle is 11 years from sunspot maximum to minimum (22 years for full cycle)maximum to minimum (22 years for full cycle)

10,000 km across10,000 km across A sunspot develops at a place where the A sunspot develops at a place where the

magnetic field pokes through the photospheremagnetic field pokes through the photosphere A plage is a bright spot associated with an A plage is a bright spot associated with an

emerging magnetic field that compresses and emerging magnetic field that compresses and heats up gases.heats up gases.

Differential rotation of the Sun leads to Differential rotation of the Sun leads to overlapping magnetic fields which leads to overlapping magnetic fields which leads to unstable conditions on the photosphereunstable conditions on the photosphere

Sunspots can be used Sunspots can be used to determine the rate to determine the rate of the sunof the sun’’s rotation. s rotation.

ProminancesProminances

Arched volumes of hot gas pushed up by Arched volumes of hot gas pushed up by magnetic field.magnetic field.

Upward of 50,000 KUpward of 50,000 KAlmost always associated with sunspotsAlmost always associated with sunspots

Solar FlaresSolar Flares

Violent, eruptive eventViolent, eruptive eventAssociated with sunspot activityAssociated with sunspot activityReleases vast quantities of high energy Releases vast quantities of high energy

particles and x-ray and uv rays.particles and x-ray and uv rays.Powerful, will leave SunPowerful, will leave Sun’’s surface quaking s surface quaking

for an hour or morefor an hour or more

Coronal Mass EjectionsCoronal Mass Ejections

Largest ejection eventLargest ejection event8 minutes for light8 minutes for light2-4 days for charged particles2-4 days for charged particlesThese ejections overwhelm the Van Allen These ejections overwhelm the Van Allen

Belts (earthBelts (earth’’s magnetic field) and lead to s magnetic field) and lead to dramatic aurorae and potential disruptions dramatic aurorae and potential disruptions of communications.of communications.

Viewing the Sun with an H-Alpha filter reveals an Viewing the Sun with an H-Alpha filter reveals an active chromosphere during a sunspot maximumactive chromosphere during a sunspot maximum

Ionized gases trapped by magnetic fields form prominences that arc far above the solar surface.

Sometimes these gases are ejected into space.

Violent eruptions called solar flares eject huge amounts of solar gases into space.

By following the trails of gases released during a By following the trails of gases released during a solar flare, we can map the Sunsolar flare, we can map the Sun’’s global magnetic s global magnetic field. field.

Coronal Mass Ejections (CMEs) typically expel 2 Coronal Mass Ejections (CMEs) typically expel 2 trillion tons of matter at 400km per second.trillion tons of matter at 400km per second.

An x-ray view of a coronal mass ejection

It reaches Earth two to four days later, and is fortunately deflected by our magnetic field.

Changes in Changes in Physical Physical Properties of Properties of Solar Gases Solar Gases from the Solar from the Solar Core to the Core to the PhotospherePhotosphere

A mystery involving undetected neutrinos produced in the Sun’s core prompted an investigation into the fundamental nature of these particles.

Subsequent experiments showed that neutrinos can change as they travel through space.

During the sunspot cycle, the latitude at which sunspots appear changes.

A plot of the latitude of appearing sunspots over time reveals that early in the sunspot cycle, they appear away from the equator, then slowly move toward the equator as the cycle progresses.

DEATH OF THE SUNDEATH OF THE SUN

The Sun does not have enough mass to explode The Sun does not have enough mass to explode as a supernova (low mass star).as a supernova (low mass star).

It is to become a red giant that will alternately It is to become a red giant that will alternately expand and contract in response to variations in expand and contract in response to variations in inward and outward pressure.inward and outward pressure.

At some point, the star will expand and then At some point, the star will expand and then slowly release its outer gas layer. Up to 80 % slowly release its outer gas layer. Up to 80 % mass loss.mass loss.

The carbon-oxygen core cools and is called The carbon-oxygen core cools and is called white dwarf.white dwarf.

WHAT DID YOU THINK?How does the mass of the Sun compare

with that of the rest of the solar system?The Sun contains 99.85% of the solar

system’s mass.Are there stars nearer the Earth than the

Sun?No, the Sun is our closest star.Does the Sun have a solid and liquid

interior like the Earth?No, the Sun is composed of hot gases.

WHAT DID YOU THINK?What is the surface of the Sun like?The Sun has no solid surface, and no solid

or liquids anywhere. The surface we see is composed of hot, churning gases.

Does the Sun rotate?The Sun’s surface rotates differentially;

once every 35 days near its poles, and once every 25 days near its equator.

What makes the Sun shine?Thermonuclear fusion in the Sun’s core

Cerenkov radiationchromosphereconvective zonecore (of the Sun)coronacoronal holecoronal mass ejectionfilamentgranulehelioseismologyhydrogen fusionhydrostatic equilibrium

limb (of the Sun)limb darkeningmagnetic dynamoneutrinophotosphereplageplasmapositronprominenceradiative zonesolar cyclesolar flaresolar luminosity

solar modelsolar windspiculesunspotsunspot maximumsunspot minimumsupergranulethermonuclear fusiontransition zoneZeeman effect

Key TermsKey Terms

You will discover…You will discover…•why the Sun is a typical starwhy the Sun is a typical star

•how todayhow today’’s technology has led to a new s technology has led to a new understanding of solar phenomena, from sunspots to understanding of solar phenomena, from sunspots to the powerful ejections of matter that sometimes enter the powerful ejections of matter that sometimes enter our atmosphereour atmosphere

•that some features of the Sun generated by its varying that some features of the Sun generated by its varying magnetic field occur in cyclesmagnetic field occur in cycles

•how the Sun generates the energy that makes it shinehow the Sun generates the energy that makes it shine

•new insights into the nature of matter from solar new insights into the nature of matter from solar neutrinosneutrinos

The Sun undergoes differential rotation.

The rotation period of the Sun’s gases varies from 25 days in the equatorial region to 35 days near the solar poles.

WHAT DO YOU THINK?How does the mass of the Sun compare

with that of the rest of the solar system?Are there stars nearer the Earth than the

Sun?Does the Sun have a solid and liquid

interior like the Earth?What is the surface of the Sun like?Does the Sun rotate?What makes the Sun shine?

Coronal holes are conduits for gases to flow out from the SunCoronal holes are conduits for gases to flow out from the Sun