Earth Science
Chapter 20
Section 2
A. The Sun:
The sun is the center of our solar system.
It controls the motion of the planets, asteroids, meteors and comets
that revolve around it.
The sun is the only star close enough to permit direct study of its
surface.
B. The Sun's Interior:
As with all stars, the energy of the sun results from nuclear
reactions in which hydrogen atoms fuse to form helium.
C. Size, Shape:
The sun is a glowing ball of hot, luminous gas with a diameter of
1.4 million Km or about 109 times as large as the earth.
In spite of its large diameter, it is considered to be a star of only
average size and temperature.
Because the inner regions of the sun appear lighter and brighter
than the outer edges, it is assumed that the sun's light originates in
its interior.
The brightness of the central portion of the sun prevents us from
seeing much of its atmosphere.
D. The Sun’s Atmosphere:
Just above the interior is the Photosphere, this is a thin yellow
layer of the solar atmosphere.
Above the photosphere is a layer known as the Chromosphere,a
bright red layer of glowing hydrogen, helium and calcium gases.
In addition to the Chromosphere, another layer called the Corona,
consists of a thin cloud of gas and extends for several hundred
thousand Km into space.
The corana sends out a stream of electrically charged particles
called a solar wind. The solar wind cause the auroras on Earth.
E. Features on the Sun:
Sunspots were first seen on the surface of the sun by Galileo in
1610.
Sunspots are believed to be areas of turbulence (eruptions) in the
lower atmosphere of the sun.
They look dark because their temperature is lower than the
photosphere surrounding them.
The larger spots have diameters of close to 160,000 Km.
Sunspots are only temporary features on the sun's surface. They
seem to reach a maximum occurrence every 11 years.
Sunspots were first used to follow the rotation of the sun on its
axis. The rate of the sun's rotation is about 25 days at its equator.
A. Prominences are huge loops of gas that connect different
partsof sunspot regions.
B. Solar flares Explosion of hydrogen gas that explode into
space. Theses explosions increase solar winds.