Section 2: Solar Activity Preview Key Ideas Sunspots The Sunspot Cycle Solar Eruptions Auroras Maps in Action

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.

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.

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 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.

Sunspots Click below to watch the Visual Concept.

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.

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.

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.

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.

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.

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.

Maps in Action XRT Composite Image of the Sun