Download 24 The Sun - Solar Physics Group

The Sun
A modest G2 star,
conveniently located
150,000,000 km from Earth.
Solar Interior
The core is the
energy source,
where hydrogen
fuses into helium.
Heat from the core
spreads out
through the
radiative and
convective zones.
How do we know...?
Neutrinos from
nuclear fusion in
the Sun’s core
can be detected
at Earth.
Sudbury Neutrino Observatory
(Sky and Telescope)
How do we know...?
Helioseismology
uses vibrations of
the Sun’s surface
to map its interior.
NJIT
Photosphere
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The part we see!
Nearly all the energy
from fusion is radiated
into space from the
photosphere.
Sunspots let us see
rotation (27 days)
Photosphere — Sunspots
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
SST (Royal Swedish Academy of Sciences)
SST (Royal Swedish Academy of Sciences)
What are Sunspots?
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Strong magnetic fields coming up from
the solar interior.
The field is strong enough to inhibit
convection, so the surface cools &
darkens.
They last from days to weeks, then
fragment and spread out.
Chromosphere
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Actually above the
photosphere!
Seen by making
images of spectral
absorption lines
The structure
reflects the Sun’s
magnetic field.
Corona (solar eclipse)
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What’s this?
Sun’s outer
atmosphere
Tenuous,
transparent
Only one millionth
as bright as
photosphere.
Corona in X-rays
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Millions of degrees
(much hotter than
photosphere!)
Photosphere does
not emit X-rays.
Coronal loops
Filamentary
structure
traces the
magnetic field
TRACE
Temperatures
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The power source is in the core
(Temperature 15 MK).
Temperature decreases until we get to the
photosphere (5800 K).
The chromosphere is hotter (up to 20,000K).
Above this is a hot corona (1-10 MK) that
extends into space.
What heats the corona?
We think it’s the Sun’s magnetic field, but
the process is not well understood!
Corona compared to sunspots
Solar Cycle

Magnetic activity comes and goes on an 11-year
cycle
11 year cycle
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Coronal activity
increases with the
sunspots
1991
1995
High activity
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Many sunspots
Coronal mass
ejections
Flares
Solar Flare
TRACE
Aurora Australis and Borealis
Earth’s magnetosphere
Low activity
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Less x-rays
produced
Fewer sunspots
Jupiter has a very large
magnetosphere. Does it
exhibit aurora?
A.
B.
C.
D.
Yes
No, its too far
away
No, its not solid
Cannot conclude
Compare x-ray and visible
Movie
Sun
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Layers:
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Corona
Chromosphere
Photosphere
Core
Activity cycle
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Sunspots, mass ejections
You are making a mobile with a
basketball for the Sun. What
could you use for the other
planets ?
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Sun: 1.4 million Km
Mercury: 4,880 Km
Venus: 12,100 Km
Earth:12,756 Km
Mars: 6,787 Km
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Jupiter: 142,800 Km
Saturn: 120,600 Km
Uranus: 51,300 Km
Neptune: 49,100 Km
SOHO