Transcript The Sun and Its Solar System Topic 1

CHAPTER 22
THE SUN and ITS SOLAR
SYSTEM
I. The Sun
Topic 1: Studying the Sun
(a)
(b)
(c)
It is dangerous to look mat the sun because it
can cause blindness.
The telescope was the instrument (by Galileo)
used to make the first scientific observations
of the sun.
A solar telescope is a special telescope that
projects a large image of the sun into a dark
underground room. With special glasses
similar to those used by welders, solar
physicists can safely watch the sun’s image
and observe changes that occur on the sun’s
surface.
Topic 1: Studying the Sun
(d) Satellites have made it possible to
study the sun and its radiation without
the interference of Earth’s atmosphere.
Orbiting Solar Observatories (OSO-1
through OSO-8) returned data from the
sun from 1962-1979. Helios A and
Helios B were placed in long, oval orbits
that carried them inside the orbit of
Mercury. The Solar Maximum Satellite
(or Solar Max) launched in 1980
functioned until 1989 and Ulysses
launched in 1990 will fly over the sun’s
pole.
Topic 2: Properties of the Sun
Our sun is an average-sized star. Its
diameter of 1 380 000 km is about 110
times Earth’s diameter. The sun’s
volume could hold more than 1 million
Earths. Its mass is 745 times greater
than all the planets together.
BACKGROUND: For a particle travelling at
the speed of light, it would take 8
minutes and 20 seconds (on our clock)
to travel between the sun and Earth.
(a)
Topic 2: Properties of the Sun
(b) Temperatures on the sun are
extreme. Its surface temperature is
about 5500oC and its interior
temperature may be as high as
15 000 000oC.
Topic 3: The Sun’s Atmosphere
(a) The sun’s atmosphere is divided into three
regions. The photosphere is the apparent
yellow surface of the sun. It is about 400 km
thick and appears to be made of millions of
individual cells, called granules about 1500 km
across with a bright center and dark edges.
Granules are the tops of the columns of gases
that form in the region below the photosphere.
The gases are rising at the centre of the
granule and sinking back down at the edges.
Individual granules last about 8 minutes before
sinking.
Topic 3: The Sun’s Atmosphere
(a) The photosphere is the lower,
denser (2.8 x 10-8 g/cm3) part of the
sun’s atmosphere.
Above the photosphere is the sun’s
outer, less dense atmosphere. At the
lower part of the outer atmosphere
us the chromosphere, colored red
by glowing hydrogen. It extends
thousands of km above the
photosphere.
Topic 3: The Sun’s Atmosphere
(a) Above the chromosphere is the
corona. It has so little gas that it
would be considered a vacuum on
Earth. It surrounds the sun to a
height of more than 1 million km. It
is seen during a total eclipse as a
faint, pearly light.
Topic 3: The Sun’s Atmosphere
(b) Solar prominences are huge,
red, flamelike arches of material that
occur in the corona. Their light is
the result of changes that occur in
cooler, denser parts of the corona.
They may last for many hours and
some extend millions of km above
the photosphere.
Topic 4: Sunspots
(a) Sunspots are dark spots on the
photosphere. Some are barely visible
and others are larger than Earth’s
diameter. Some last a few hours while
others remain visible for a few months.
They typically have a dark centre
(umbra) and a lighter rim (penumbra).
Topic 3: The Sun’s Atmosphere
(a) Sunspots occur in pairs. One is the a
north magnetic pole and the other a
south magnetic pole. The concentration
of magnetic forces at these locations
slows down solar activity and causes the
photosphere to cool by as much as
1500oC.
Topic 4: Sunspots
(b) Sunspots appear to move left to
right across the sun’s surface. This
motion is caused by the sun’s
rotation. Since the sun is made of
gases, its rotation rate is not
uniform. At the equator the sun
takes about 25 Earth days for one
rotation and 27 days at the poles.
Topic 4: Sunspots
(c) The number of sunspots visible on the
photosphere changes daily. During peak
sunspot activity, over 100 may be
counted. During periods of low sunspot
activity, several days may pass when no
spots are visible. These changes occur in
a sunspot cycle that averages about 11
years from one period of peak activity to
the next.
Topic 5: The Solar Wind and
Magnetic Storms
(a) Solar wind is the constant
stream of electrically charged
particles given off by the corona.
These particles fly into space in all
directions, some at an average speed
of 400 km/s by the time they reach
Earth. Solar events produce huge
gusts of solar wind.
Topic 5: The Solar Wind and
Magnetic Storms
(b) Great tears, called coronal holes,
sometimes appear in the corona.
Some extend halfway around the
sun, and many do not close for many
months. Solar wind pours from
coronal holes in a great torent of
particles.
Topic 5: The Solar Wind and
Magnetic Storms
(b) Solar flares are another source of
solar wind bursts. They are
outbursts of light that arise suddenly
in areas of sunspot activity. Most
flare up in a few minutes then fade
rapidly. The number of solar flares
increases as the number of sunspots
increase.
Topic 5: The Solar Wind and
Magnetic Storms
(c) As the solar wind blows past Earth,
some particles interact with Earth’s
magnetic field and upper
atmosphere, causing auroras, or
northern and southern lights.
Magnetic storms occur on Earth
when the particles thrown out by
coronal holes and solar flares are
added to the constant solar wind
produced by the corona.
Topic 5: The Solar Wind and
Magnetic Storms
(c) At such times auroras may be seen
in middle latitudes as well as in polar
areas, and compass needles may
give inaccurate readings. Electrical
surges may disrupt telephone
reception and damage unprotected
electrical appliances. Radio
reception in AM, citizen’s band (CB),
and shortwave frequencies may be
affected.
Topic 6: Source of the Sun’s
Energy
(a) The sun is mostly hydrogen. Four
hydrogen nuclei have a mass of
4.030 amu. In fusion 4 hydrogen
nuclei join to form a helium nucleus
that has a mass of only about 4.003
amu. This mass difference is
converted into electromagnetic
radiation which is transmitted into
space.
Topic 6: Source of the Sun’s
Energy
(a) Astronomers calculate that about
4 million metric tons of matter are
being changed to energy every
second in the sun. 564 million
metric tons of hydrogen becomes
560 million tons helium.
Topic 6: Source of the Sun’s
Energy
(b) The mass of the sun is so great
that this process can continue for
another 5 billion years.