the sun chapter 10. the sun - our star “average” star made entirely of gas –too hot for...

The Sun

Chapter 10

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The Sun - Our Star

• “Average” star• Made entirely of gas

– too hot for liquids or solids• Surface temp = 5000 K• Center temp = 10 million K

• Composition (by mass):– 70% H– 28% He– 2% everything else (C, N, O, etc.)

Major Regions of the Sun

• Interior– Core

– Radiative Zone

– Convective Zone

• Atmosphere– Photosphere

– Chromosphere

– Corona

Photosphere

• Effective “surface” of sun– not solid– region we see by eye

• Thin atmospheric layer– Few hundred km

• Low density gas– 0.01% Earth’s atmosphere

• Close-up shows granulation– convection cells

• Sunspots– Cooler than surrounding gas

• appear dark


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Atmospheric Features

• Sunspots– Larger than Earth– Occur in groups– Associated with magnetic fields– Galileo used to measure solar

rotation • 25 days at equator• longer at poles

– Number of sunspots• Cyclical

– 11 yr period

• Correlated with solar activity– greatest activity at sunspot maximum– least at minimum

Most Detailed Sunspot Image Ever!

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Swedish Vacuum Telescope

Solar Rotation



• Sunspots– Larger than Earth– Occur in groups– Associated with magnetic fields– Galileo used to measure solar

rotation • 25 days at equator• longer at poles

– Number of sunspots• Cyclical

– 11 yr period

• Correlated with solar activity– greatest activity at sunspot maximum– least at minimum


• Prominences– Loops of hot gas– Base near sunspots – Trace magnetic fields


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Chromosphere

• Region just above photosphere

• Emission-line spectrum– indicates higher temperature

– reddish color from hydrogen line

• Temperature increases outward

Transition Region

• Between chromosphere and corona

• Temperature increases– from 10,000 K to 106 K

• Spicules (“spikes”) – gas jets poking up from

photosphere– duration ~10 minutes– heights 5,000-20,000 km


Corona

• Outermost region of atmosphere– Extends millions of km

• Seen during eclipse • Very high temperature

– millions of degrees K

– heated by solar magnetic field


Solar Wind

• Gas flows away from sun– 10 million tons/yr– protons & electrons– speed 400-800 km/s

• Material goes outward into solar system– Hits Earth’s atmosphere

• guided by magnetic field• makes atmosphere glow

(aurorae)



Solar Flare

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Solar Flares

• Eruptions caused by magnetic fields – may last 5-10 min

– release huge amounts of energy• gas heated to 107 K

– produces X-rays and UV radiation

• Coronal Mass Ejections– very large flares

– large mass of gas ejected from corona



Solar Flares & Effects on Earth

• CME hits Earth’s Magnetic Field– Aurorae intensified

– affects magnetic field • produces power surges

– ’89 Quebec/Montreal power outage

– electrical interference• Disrupts radio communications

– Cell phone outage

• Danger to satellites/astronauts• Space Weather at:

http://www.sel.noaa.gov/today.html

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Solar Variability & Earth’s Climate

• Solar Luminosity Varies ~1%– Highest at sunspot maximum– Lowest at minimum activity

• Maunder minimum 1650-1700– Very few sunspots– “Little Ice Age” in Europe

• extreme cold temps• shorter growing season

• Still learning how Sun affects Earth’s climate QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Solar Interior

• Interior is gaseous

• Constant battle:– Gravity pulls in– Pressure pushes out

• Star shrinks – becomes hotter, until

• Pressure balances gravity

Hydrostatic Equilibrium

Why Does Sun Shine?• Sun in Hydrostatic Equilibrium

– Pressure requires high temperature– Sun is hot

• Hot objects– Radiate (emit light)– lose energy

• Solar Luminosity– 1026 Watts

• Age of Sun– greater than 4.5 billion years (age of earth)

• What is energy source?

Sun shines because it is hot

Sun’s Energy Source• Thermal energy (chemical reactions)?

– wood or fuel burning– Entire Sun used in a few thousand years NO

• Gravitational contraction?– energy released as Sun contracts– would suffice for 100 million years NO

• Nuclear Energy?– Einstein: E = mc2

– Can convert mass into energy• 1 gram of matter = energy of 15,000 barrels of oil

– Need 4 million tons/sec– Will suffice for 10 billion years YES

Nuclear Reactions

• Fusion: – two light nuclei joined

into one• Powers Sun

• Fission: – massive nucleus splits

in two• Powers nuclear

reactors (Davis-Besse)QuickTime™ and aYUV420 codec decompressorare needed to see this picture.


Converting Mass to Energy

• Nuclear reactions change mass– Mass increase consumes energy

– Mass decrease releases energy

• Mass decreases in

– Fission of heavy nuclei• Can occur spontaneously

• natural radioactivity

– Fusion of light nuclei• Like charges repel

• Fusion requires high speed

• Temperature > 10 million K


Fusion: Sun’s Energy Source

• Sun’s core:– Temperature = 15 million K

– Large enough to fuse hydrogen

• p-p chain (proton-proton)– Series of fusion reactions

– Converts:4 hydrogen to 1 helium nucleus

– mass of 4 H > mass of 1 He• mass decrease is energy source




p-p Chain in the Sun

the sun chapter 10. the sun - our star “average” star made entirely of gas –too hot for...

Documents

solar rotation slide

minimum slide

solar flare slide

solar magnetic field

outward slide

dark slide

earths climate slide

solar interior interior