Of course, the spheres are graced with interesting features and activity. We'll take a look at them here.
Dark, cool areas called sunspots appear on the photosphere. Sunspots always appear in pairs and are intense magnetic fields (about 5,000 times greater than the Earth's magnetic field) that break through the surface. Field lines leave through one sunspot and re-enter through the other one. The magnetic field is caused by movements of gases in the sun's interior.
Sunspot activity occurs as part of an 11-year cycle called the solar cycle where there are periods of maximum and minimum activity.
It is not known what causes this 11-year cycle, but two hypotheses have been proposed:
- Uneven rotation of the sun distorts and twists magnetic field lines in the interior. The twisted field lines break through the surface forming sunspot pairs. Eventually, the field lines break apart and sunspot activity decreases. The cycle starts again.
- Huge tubes of gas circle the sun's interior at high latitudes and begin to move toward the equator. When they roll against each other, they form spots. When they reach the equator, they break up and sunspots decline.
Occasionally, clouds of gases from the chromosphere will rise and orient themselves along the magnetic lines from sunspot pairs. These arches of gas are called solar prominences.
Prominences can last two to three months and can extend 30,000 miles (50,000 kilometers) or more above the sun's surface. Upon reaching this height, they can erupt for a few minutes to hours and send large amounts of material racing through the corona and outward into space at 600 miles per second (1,000 kilometers per second); these eruptions are called coronal mass ejections.
Sometimes in complex sunspot groups, abrupt, violent explosions from the sun occur. These are called solar flares.
Solar flares are thought to be caused by sudden magnetic field changes in areas where the sun's magnetic field is concentrated. They're accompanied by the release of gas, electrons, visible light, ultraviolet light and X-rays. When this radiation and these particles reach the Earth's magnetic field, they interact with it at the poles to produce the auroras (borealis and australis). Solar flares can also disrupt communications, satellites, navigation systems and even power grids. The radiation and particles ionize the atmosphere and prevent the movement of radio waves between satellites and the ground or between the ground and the ground. The ionized particles in the atmosphere can induce electric currents in power lines and cause power surges. These power surges can overload a power grid and cause blackouts. You can learn more about solar flares by reading Could an extremely powerful solar flare destroy all the electronics on Earth?
All of this activity requires energy, which is in limited supply. Eventually, the sun will run out of fuel.