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Chapter 24: Studying the Sun 24.3: The Sun Textbook pages 684-690

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Chapter 24: Studying the Sun

24.3: The Sun

Textbook pages 684-690

• 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.)

Auroras occur

only at the north

and south poles.

All of these photos

were taken in

Northern Alaska.

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.

The interaction of

magnetic fields and

solar winds is the

“aurora borealis.”