The Sun
Section 2: Solar Activity
Preview
• Key Ideas
• Sunspots
• The Sunspot Cycle
• Solar Eruptions
• Auroras
• Maps in Action
Section 2
The Sun
Section 2
Key Ideas
• Explain how sunspots are related to powerful magnetic
fields on the sun.
• Compare prominences, solar flares, and coronal mass
ejections.
• Describe how the solar wind can cause auroras on
Earth.
The Sun
Section 2
Sunspots
• sunspot a dark area of the photosphere of the sun that
is cooler than the surrounding areas and that has a
strong magnetic field.
• The movements of gases within the sun’s convective
zone and the movements caused by the sun’s rotation
produce magnetic fields.
• These magnetic fields cause convection to slow in parts
of the convective zone.
The Sun
Section 2
Sunspots
• Slower convection causes a decrease in the amount of
gas that is transferring energy from the core of the sun to
these regions of the photosphere.
• Because less energy is being transferred, these regions
of the photosphere are considerably cooler than
surrounding regions, and form areas of the sun that
appear darker than their surrounding regions.
• These, cooler, darker areas are called sunspots.
• The rest of the photosphere has a grainy appearance
called granulation.
The Sun
Section 2
The Sunspot Cycle
• Observations of sunspots have shown that the sun
rotates.
• The numbers and positions of sunspots vary in a cycle
that lasts about 11 years.
• Sunspots initially appear in groups about midway
between the sun’s equator and poles. The number of
sunspots increases over the next few until it reaches a
peak of 100 of more sunspots.
• After the peak, the number of sunspots begins to
decrease until it reaches a minimum.
The Sun
Sunspots
Click below to watch the Visual Concept.
Section 2
The Sun
Section 2
Solar Eruptions
• Other solar activities are affected by the sunspot cycle,
such as the solar-activity cycle.
• The solar-activity cycle is caused by the changing solar
magnetic field.
• This cycle is characterized by increases and decreases
in various types of solar activity, including solar
eruptions.
• Solar eruptions are events in which the sun lifts
substantial material above the photosphere and emits
atomic or subatomic particles.
The Sun
Section 2
Solar Eruptions, continued
• Solar eruptions include prominences, solar flares, and
coronal mass ejections.
Prominences
• prominence a loop of relatively cool, incandescent gas
that extends above the photosphere.
• Each solar prominence follows the curved magnetic field
lines from a region of one magnetic polarity to a region of
the opposite magnetic polarity.
The Sun
Section 2
Solar Eruptions, continued
Solar Flares
• solar flare an explosive release of energy that comes
from the sun and that is associated with magnetic
disturbances on the sun’s surface
• Solar flares are the most violent of all solar disturbances.
• Solar flares release the energy stored in the strong
magnetic fields of sunspots. This release can lead to the
formation of coronal loops.
• Some particles from a solar flare escape into space.
These particles increase the strength of the solar wind.
The Sun
Section 2
Solar Eruptions, continued
Coronal Mass Ejections
• coronal mass ejection coronal gas that is thrown into
space from the sun
• As gusts of particles strike Earth’s magnetosphere, or
the space around Earth that contains a magnetic field,
the particles can generate a sudden disturbance to
Earth’s magnetic field, called a geomagnetic storm.
• Geomagnetic storms have been known to interfere with
radio communications, satellites, and even cause
blackouts.
The Sun
Section 2
Solar Eruptions, continued
Reading Check
How do coronal mass ejections affect communications on
Earth?
Coronal mass ejections generate sudden disturbances in
Earth’s magnetic field. The high-energy particles that
circulate during these storms can damage satellites, cause
power blackouts, and interfere with radio communications.
The Sun
Section 2
Auroras
• aurora colored light produced by charged particles from
the solar wind and from the magnetosphere that react
with and excite the oxygen and nitrogen of Earth’s upper
atmosphere; usually seen in the sky near Earth’s
magnetic poles.
• Auroras are the result of the interaction between the
solar wind and Earth’s magnetosphere.
• Auroras are usually seen close to Earth’s magnetic poles
because electrically charged particles are guided toward
earth’s magnetic poles by Earth’s magnetosphere.
The Sun
Maps in Action
XRT Composite Image of the Sun
Section 2