Transcript The Electromagnetic Spectrum

Introducing the Sun!
The Sun in Mythology
• The Greeks and
Romans believed
the Sun was the
god Apollo driving a
chariot across the
sky.
• Egyptians also
worshiped their
Sun God.
Modern Views of the Sun
By viewing the Sun
with different parts
of the
electromagnetic
spectrum, we can
see different
properties of our
star.
The Copernican System
• The Sun became the center of the
known universe.
• The universe and the Sun proved to be
much larger than once believed.
• Then it was discovered that the Sun is
not in the middle of our own galaxy.
• It was thought be constant, made of a
pure substance with no internal
structures.
The Wobbling Sun
• Newton’s Laws of Motion and Gravitation force us to
modify the Copernican viewpoint.
• The Sun and the planets actually revolve around a
common center of mass, which in all cases is inside
the Sun itself.
• This causes the Sun to wobble a small amount.
Galileo discovered the sun
had impurities…sunspots
The sunspots move
across the sun’s surface.
It rotates!
This layer of the Sun, which
we see is the photosphere.
March 25, 2008
Close up of a Sunspot…
GRANULES
UMBRA
Photosphere
PENUMBRA
The Sunspot Cycle
• Soon after
Galileo’s
discovery, records
were kept of
sunspots.
• It was discovered
that they increase
and decrease in a
more-or-less
orderly fashion.
A BIG Sunspot Graph
• Assemble the graphs together to make one
large plot of sunspots from 1700 to 2008.
• Choose any five maxima. When were they?
How many years separate them on average?
• Do the same for the minima.
• How often do you see exceptionally high
maxima? Are they followed by very low
minima?
• Predict what the graph will look like for the
next six years (2009 - 2018).
How is your prediction?
March 2009
The next sunspot
minimum is now ending
in 2008 - a very low
minimum! There were
over 200 days last year
without any sunspots!
And currently there are
NO sunspots
The next maximum is
scheduled for 2012,
and it should be large.
The Butterfly Effect
• Sunspots in both hemispheres of the sun
move toward the equator in mirror images.
The Magnetic Sun
Charged particles
flowing through the
sun produces
magnetic fields.
Areas of strong
magnetism
produce sunspots
on the surface.
Horace Babcock
How do we detect magnetic fields?
• Spectral lines are
split into triplets in
the presence of
strong magnetic
fields.
• This is known as the
Zeeman Effect.
• Sunspots show the
Zeeman Effect most
strongly.
Minimum
Differential Rotation
Maximum
The Magnetic Cycle
matches the Sunspot Cycle
Differential Rotation
• The sun rotates faster on the equator than on
the poles.
• This is due to the fact that the sun is a fluid.
• This differential rotation distorts the magnetic
fields.
• When fields are aligned, the sunspots are at
a minimum. When distorted, the number of
spots increases.
• This is the basis behind the Babcock Model.
Relationship of Sunspots to
the Sun’s Magnetic Field…
Sunspot Groups Act
Like Bar Magnets
• Sunspots often form
pairs, with one a “North
Pole” and the other the
“South.”
• The magnetic field
connects these two
groupings with an arch.
• This is often
accompanied by a solar
prominence.
Solar Flare 2002
Close-up of the Photosphere
GRANULES
Granulation Animation
What Causes the Granules?
• Hot gases rise in
the middle of the
granule.
• Cooler gases sink
along the edges.
• These are
convection currents
heated from below.
The
Sun’s
Interior:
Intense
heat in
the core
fuels
solar
activity.
Hydrogen fusion to Helium
• The sun’s core is
10 million °K.
• At this
temperature,
hydrogen nuclei
fuse into helium
• Huge amounts of
energy are
released.
Solar Storms can extend
thousands of miles into space.
Coronal Mass Ejections
• During times of solar
maxima, the sun
ejects gas into
space.
• They are called
coronal mass
ejections (CMEs).
• These electrically
charged gases can
travel far beyond the
Sun…solar wind.
Effect on the Earth’s
Magnetic Field
AURORA BOREALIS
The Chromosphere
This thin layer just
above the
photosphere is best
seen during a total
solar eclipse.
Solar flares,
spicules, and
prominences are
found in this thin
gaseous layer.
The Corona: the outermost
layer of the Sun
The Corona’s shape is
dependent on solar activity below
1
3
2
4
5
1
2
3 4
5
• The corona is
stretched out
during sunspot
minima.
• Sunspot maxima
occur during
times of great
solar storms.
Babcock Model: a Summary
Sunspot
MagMaximum netic
fields
twisted
and distorted.
Solar
Storms
frequent.
Watch for
auroras!
Corona
Solar
extends in wind is
all
strong.
directions
Sunspot
Minimum
Few
solar
storms
Corona
Solar
found only wind is
near solar calm.
equator
Magnetic
fields
aligned
north to
south.
The Solar Spectrum
Hot sun
Cool thin
gas
• A spectroscope pointed at the sun reveals
an absorption spectrum.
• The dark lines identify elements,
especially hydrogen (above) and helium.
How Do We Know that
Helium is in the Sun?
• A glowing He fluorescent
tube creates the
emission spectrum
shown on the right.
• These same spectral lines
are found on the Sun as
well, in fact they were
actually seen there first.
• This is why helium means
“sun element.”
Hot glowing thin
gases give off
emission
spectra.
The peak of the sun’s
radiation is 500 nm, so…
The Sun is yellow.
This means its
surface
temperature is
5800 °K or
10,000 F.
The General Theory of Relativity
• Albert Einstein
proposed his General
Theory of Relativity in
1918.
• It stated that gravity is
a “dimple” in the
space-time
continuum.
• Light bends as it goes
by the sun, and
Mercury’s orbit is also
affected.
SUN
Quiz!!
• What are the three major layers of the
Sun and what properties do they have?
• Explain briefly what Babcock stated
about the role of magnetism in the
sunspot and solar storm cycles.
• What is meant by the term differential
rotation?
• What phenomenon proved Einstein’s
Theory of General Relativity?