Introducing the Sun!

1
Introducing the Sun!
2
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.

3
Modern Views of the Sun
By viewing the Sun with different parts of the
electromagnetic spectrum, we can see different
properties of our star.
4
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.

5
The Wobbling Sun

• Newtons 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.

6
Galileo discovered the sun had impuritiessunspots
The sunspots move across the suns surface. It
rotates!
7
This layer of the Sun, which we see is the
photosphere.
March 25, 2008
8
Close up of a Sunspot
GRANULES
UMBRA
Photosphere
PENUMBRA
9
The Sunspot Cycle

• Soon after Galileos discovery, records were kept
  of sunspots.
• It was discovered that they increase and decrease
  in a more-or-less orderly fashion.

10
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).

11
How is your prediction?
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.
March 2009
12
The Butterfly Effect

• Sunspots in both hemispheres of the sun move
  toward the equator in mirror images.

13
The Magnetic Sun
Charged particles flowing through the sun
produces magnetic fields. Areas of strong
magnetism produce sunspots on the surface.
Horace Babcock
14
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.

15
The Magnetic Cycle matches the Sunspot Cycle
Minimum
Differential Rotation
Maximum
16
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.

17
Relationship of Sunspots to the Suns Magnetic
Field
18
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
19
Close-up of the Photosphere
GRANULES
Granulation Animation
20
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.

21
The Suns InteriorIntense heat in the core
fuels solar activity.
22
Hydrogen fusion to Helium

• The suns core is 10 million K.
• At this temperature, hydrogen nuclei fuse into
  helium
• Huge amounts of energy are released.

23
Solar Storms can extend thousands of miles into
space.
24
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 Sunsolar wind.

25
Effect on the Earths Magnetic Field
AURORA BOREALIS
26
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.
27
The Corona the outermost layer of the Sun
28
The Coronas shape is dependent on solar activity
below

• The corona is stretched out during sunspot
  minima.
• Sunspot maxima occur during times of great solar
  storms.

3
4
1
5
2
1
2
4
3
5
29
Babcock Model a Summary
Sunspot Maximum Mag-netic fields twisted and dis-torted. Solar Storms frequent. Watch for auroras! Corona extends in all directions Solar wind is strong.
Sunspot Minimum Mag- netic fields aligned north to south. Few solar storms Corona found only near solar equator Solar wind is calm.
30
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.

31
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.
32
The peak of the suns radiation is 500 nm, so
The Sun is yellow. This means its surface
temperature is 5800 K or 10,000 F.
33
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 Mercurys
  orbit is also affected.

SUN
34
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 Einsteins Theory of
  General Relativity?