Section 2: Solar Activity

1. Section 2: Solar Activity Preview • Objectives • Sunspots • The Sunspot Cycle • Solar Ejections • Auroras • Maps in Action

2. Objectives • 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.

3. Sunspots • sunspota 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.

4. 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 fo the sun that appear darker than their surrounding regions. • These, cooler, darker areas are called sunspots.

5. 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.

6. Sunspots

7. Solar Ejections • 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 ejections. • Solar ejections are events in which the sun emits atomic particles.

8. Solar Ejections, continued Prominences • prominencea loop of relatively cool, incandescent gas that extends above the photosphere. • Solar ejections include prominences, solar flares, and coronal mass ejections. • Prominences are huge arches of glowing gases that follow the curved lines of the magnetic force from a region of one magnetic force to a region of the opposite magnetic polarity.

9. Solar Ejections, continued Solar Flares • solar flarean 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.

10. Solar Ejections, continued Coronal Mass Ejections • coronal mass ejectiona part of coronal gas that is thrown into space from the sun • Some of the particles from a solar flare escape into space, increasing the strength of the solar wind. • Particles also escape as coronal mass ejections. The particles in the ejection can cause disturbances to Earth’s magnetic field. • These disturbances have been known to interfere with radio communications, satellites, and even cause blackouts.

11. Solar Ejections, 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.

12. 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.

13. Maps in Action SXT Composite Image of the Sun