The Sun

1
The Sun

• Chapter 10

2
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.)

3
Major Regions of the Sun

• Interior
• Core
• Radiative Zone
• Convective Zone
• Atmosphere
• Photosphere
• Chromosphere
• Corona

4
Photosphere

• Effective surface of sun
• not solid
• region we see by eye
• Thin atmospheric layer
• Few hundred km
• Low density gas
• 0.01 Earths atmosphere
• Close-up shows granulation
• convection cells
• Sunspots
• Cooler than surrounding gas
• appear dark

5
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

6
Most Detailed Sunspot Image Ever!
Swedish Vacuum Telescope
7
Solar Rotation
8
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

9
Atmospheric Features

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

10
Chromosphere

• Region just above photosphere
• Emission-line spectrum
• indicates higher temperature
• reddish color from hydrogen line
• Temperature increases outward

11
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

12
Corona

• Outermost region of atmosphere
• Extends millions of km
• Seen during eclipse
• Very high temperature
• millions of degrees K
• heated by solar magnetic field

13
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 Earths atmosphere
• guided by magnetic field
• makes atmosphere glow (aurorae)

14
Solar Flare
15
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

16
Solar Flares Effects on Earth

• CME hits Earths 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/t
  oday.html

17
Solar Variability Earths 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 Earths climate

18
Solar Interior

• Interior is gaseous
• Constant battle
• Gravity pulls in
• Pressure pushes out
• Star shrinks
• becomes hotter, until
• Pressure balances gravity
• Hydrostatic Equilibrium

19
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
20
Suns 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

21
Nuclear Reactions

• Fusion
• two light nuclei joined into one
• Powers Sun
• Fission
• massive nucleus splits in two
• Powers nuclear reactors (Davis-Besse)

22
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 gt 10 million K

23
Fusion Suns Energy Source

• Suns core
• Temperature 15 million K
• Large enough to fuse hydrogen
• p-p chain (proton-proton)
• Series of fusion reactions
• Converts4 hydrogen to 1 helium nucleus
• mass of 4 H gt mass of 1 He
• mass decrease is energy source

24
p-p Chain in the Sun