Transcript 9.2 The Solar Interior

Lecture Outlines
Chapter 9
Astronomy:
A Beginner’s Guide to the Universe
5th Edition
Chaisson / McMillan
© 2007 Pearson Prentice Hall
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Chapter 9
The Sun
Units of Chapter 9
The Sun in Bulk
The Solar Interior
The Solar Atmosphere
The Active Sun
The Heart of the Sun
9.1 The Sun in Bulk
Basic Structure
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Radius= 696,000 km
Mass= 1.99x10
Average Density = 1.4 g/cm3
71% Hydrogen (mass)
27% Helium (mass)
2% Metals (mass)
Surface Temperature = 5780 K (9912°F)
Core Temperature = 15,000,000 K
30
(26,993,105°F)
• Rotation period= 25-36 days, faster at equator
Basic Structure
• Photosphere - "sphere of light", the
visible surface of the Sun
• Chromosphere - "sphere of color",
visible during solar eclipses
• Corona - the Sun's outermost
atmosphere. The outflow of gas in this
region is called the solar wind, which is
protons and electrons that have
escaped the Sun's gravity.
9.1 The Sun in Bulk
Interior structure of
the Sun:
Outer layers are
not to scale.
The core is where
nuclear fusion
takes place.
The Sun's Interior
• Thermonuclear core - the central region of
Sun where fusion takes place due to high
temperatures and pressures.
• Radiation zone - a region inside a star where
energy is transported outward by the
movement of photons.
• Convection zone - a layer inside a star where
energy is transported outward by means of
heat flow through the gasses of the star
(convection).
9.2 The Solar Interior
Energy transport
The radiation zone is relatively transparent; the
cooler convection zone is opaque:
9.1 The Sun in Bulk
Luminosity – total energy radiated by the Sun –
can be calculated from the fraction of that
energy that reaches Earth.
Total luminosity is about
4 × 1026 W – the
equivalent of 10 billion
1-megaton nuclear
bombs per second.
9.2 The Solar Interior
Mathematical models, consistent with
observation and physical principles, provide
information about the Sun’s interior.
In hydrostatic
equilibrium, inward
gravitational force
must be balanced by
outward pressure:
9.2 The Solar Interior
Solar density and
temperature, according
to the standard solar
model:
9.2 The Solar Interior
-the visible top layer of
the convection zone is
granulated
-areas of upwelling
material surrounded by
areas of sinking
material:
9.3 The Solar Atmosphere
Spectral analysis can tell us what elements are
present, but only in the chromosphere and
photosphere:
9.3 The Solar Atmosphere
The cooler chromosphere is above the
photosphere
-Difficult to see
directly
-Photosphere is too
bright, unless Moon
covers photosphere
and not chromosphere
during eclipse
9.3 The Solar Atmosphere
Small solar storms in chromosphere emit spicules:
9.3 The Solar Atmosphere
Solar corona can be seen during eclipse if both
photosphere and chromosphere are blocked:
9.3 The Solar Atmosphere
Corona is much hotter than layers below it –
must have a heat source, probably
electromagnetic interactions.
9.4 The Active Sun
Sunspots: appear dark
because slightly cooler
than surroundings
Usually occur in pairs
9.4 The Active Sun
Sunspots come and go,
typically in a few days.
Sunspots are linked by pairs
of magnetic field lines:
9.4 The Active Sun
The rotation of the Sun drags magnetic field
lines around with it, causing kinks
9.4 The Active Sun
-11-year sunspot cycle
-sunspot numbers rise
(increased activity), fall,
and then rise again
-change in location
(maximum closer to
equator)
9.4 The Active Sun
-really a 22-year cycle
-the spots switch polarities between the N and S
hemispheres every 11 years
-Maunder minimum: few, if any, sunspots:
9.4 The Active Sun
Areas around sunspots are active; large
eruptions may occur in photosphere.
Solar prominence is large sheet of ejected gas:
lasts days or weeks (loop)
9.4 The Active Sun
-Solar flare is a large
explosion on Sun’s
surface
-emits a similar
amount of energy to a
prominence
-lasts seconds,
minutes, or hours
9.4 The Active Sun
A coronal mass ejection
emits charged particles
that can affect the Earth:
9.4 The Active Sun
Solar wind escapes Sun
mostly through coronal holes,
which can be seen in X-ray
images
9.4 The Active Sun
Solar corona changes along with sunspot
cycle; is much larger and more irregular at
sunspot peak:
9.5 The Heart of the Sun
Nuclear fusion requires that
like-charged nuclei get close
enough to each other to fuse.
(overcome EM repulsion)
This can happen only if the
temperature is extremely high
– over 10 million K.
fusion
4 Hydrogen Atoms  1 Helium Atom + 2 neutrinos  gamma rays
(energy)
9.5 The Heart of the Sun
The process that powers most stars is a threestep fusion process. How it gets energy!
Proton-proton
chain reaction
(Gamma rays)
4 protons → 1 helium 4 + 2 neutrinos +gamma rays
9.5 The Heart of the Sun
The Sudbury
neutrino
observatory.
Particles
escaped
directly from
core of sun
Summary of Chapter 9
• Sun is held together by its own gravity and
powered by nuclear fusion
• Outer layers of Sun: photosphere,
chromosphere, corona. The corona is very hot.
• Mathematical models and helioseismology
give us a picture of the interior of the Sun
• Sunspots occur in regions of high magnetic
fields; darker spots are cooler
Summary of Chapter 9
• Nuclear fusion converts hydrogen to helium,
releasing energy
• Solar neutrinos come directly from the solar
core, although observations have told us more
about neutrinos than about the Sun
Nuclear Fusion
Nuclear Fusion