chapter 24: studying the sun · 2015-06-26 · chapter 24: studying the sun ... it’s not safe to...
TRANSCRIPT
• The sun is one of the
100 billion stars of
the Milky Way galaxy.
• The sun has no
characteristics to
make it unique to the
universe. It is an
“average star.”
• It IS, however, Earth’s
primary source of
energy.
The sun is also the only star whose
surface we can study.
•Because of its brightness and radiation,
it’s not safe to study the sun directly.
One of the finest
telescopes for observing
the sun in the world is
located at Kitt National
Observatory in southern
Arizona.
Solar Statistics
• The sun’s diameter is equal to 109 Earth diameters, or 1.35 million kilometers.
• The sun’s volume is 1.25 million times as great as Earth’s.
• Its mass is 332,000 times the mass of Earth.
• The sun’s densityis only one quarter that of earth’s.
• 90% of the sun’s surface is hydrogen.
Structure of the Sun
• We can divide the sun into four
parts:
–The solar interior
–The visible surface (photosphere)
–The two atmospheric layers:
• The Chromosphere
• The Corona
The Sun’s Visible Skin:
Photosphere
• What words can you think of that include “photo?” Write them in your notes…
• These words all refer to what phenomenon?
• What does this tell you about the
photosphere?
The photosphere radiates most of the
light that we see.
It is a layer of gas about 500 kilometers thick.
The photosphere is not smooth and uniform.
It is covered with spots known as “granules.”
Each granule is about the size of Texas.
They rise and sink in the surface due to convection.
Sun
Spot
Granules
The Red Layer: Chromosphere
• The chromosphere lies directly above
the photosphere.
• It is a few thousand kilometers thick.
• The chromosphere can only be seen
during an eclipse or with special
instruments.
• During an eclipse it appears as a
narrow, spiky red ring around the sun.
This image of the sun’s chromosphere
was taken by a special telescope camera.
You can see the photosphere in its gaps.
Corona: The Sun’s “Crown”
• The corona is the outermost layer of
the sun’s atmosphere. It rests on top of
the chromosphere.
• Like the chromosphere, the corona can
only be seen during a total solar
eclipse or with special instruments
which block light shining from the
photosphere.
This is an exceptionally dramatic photo of
the corona, taken during a total solar
eclipse.
The corona can extend millions of
kilometers into space.
Aurora Borealis
• The corona is very weak, and its
surface is easily broken.
• The streams of protons and electrons
which break through its gravitational
pull are called “solar winds.”
When solar winds reach earth,
they are pulled to the poles by
our electromagnetic field.
This results in a
display of “aurora
borealis,” or
“Northern Lights.”
(Most solar wind particles escape into space and don’t reach earth.)
The Active Sun
• The sun has a dynamic, active surface
which changes constantly.
• The most noticeable features on the sun
are the dark regions.
• Before the telescope, it was thought that
these dark areas were mini-planets in
front of the sun, NOT part of it.
• In 1610, Galileo observed that not only were these dark regions part of the sun, but that they were moving across the surface.
• Galileo concluded was that the sun rotated, AND that not all parts of the sun rotate at the same time!
Sunspots
• Sunspots are
regions on the
photosphere
which are about
1,500 C less than
the surrounding
surface.
Sunspots have a cycle of about 11 years.
At its height, more than a hundred
sunspots can be spotted at a time.
Then their
numbers decline
until only a few or
none are visible.
Prominences
• Prominences are ionized
gases trapped by magnetic
fields that extend from regions
of intense solar activity.
Solar Flare
• The most explosive events
associated with sunspots are
solar flares.
• They last about an hour, and
appear as a sudden brightening
arc above sunspot clusters.
Solar flares release enormous amounts of
energy, in the form of ultraviolet, radio,
and X-ray radiation waves.
This stream of atomic particles is called “The Solar Wind.”
About a day after a large burst of solar flares, the
particles will reach earth. They are attracted and flow
to the earth’s magnetic poles.