heat and light. The rest of the Sun is heated by movement of heat energy outward from the
core. Light energy from the Sun is emitted from the photosphere. It travels through space,
and some of it reaches the Earth. The Sun is the source of almost all the energy on Earth
and sunlight powers photosynthesis, as well as warming and illuminating our Earth.
Surface Features of the Sun
The most noticeable surface feature of the Sun is the presence of sunspots, which are
cooler, darker areas on the Sun’s surface (Figure24.19). Sunspots are only visible with
special light-filtering lenses. They exhibit intense magnetic activity. These areas are cooler
and darker because loops of the Sun’s magnetic field break through the surface and disrupt
the smooth transfer of heat from lower layers. Sunspots usually occur in pairs. When a loop
of the Sun’s magnetic field breaks through the surface, it usually creates a sunspot both
where it comes out and one where it goes back in again. Sunspots usually occur in 11 year
cycles, beginning when the number of sunspots is at a minimum, increasing to a maximum
number of sunspots and then gradually decreasing to a minimum number of sunspots again.
Figure 24.19: Sunspots. ( 18 )If a loop of the sun’s magnetic field snaps and breaks, it createssolar flares, which are
violent explosions that release huge amounts of energy (Figure24.20). They release streams
of highly energetic particles that make up thesolar wind. The solar wind can be dangerous
to spacecraft and astronauts. It sends out large amounts of radiation, which can harm the
human body. Solar flares have knocked out entire power grids and can disturb radio, satellite
and cell phone communications.
Another highly visible feature on the Sun are solar prominences. If plasma flows along a loop
of the Sun’s magnetic field from sunspot to sunspot, it forms a glowing arch that reaches
thousands of kilometers into the Sun’s atmosphere. Prominences can last for a day to several
months. Prominences are also visible during a total solar eclipse.
AbeautifulandmysteriouseffectoftheSun’selectricallychargedparticlesareauroras, which
form around the polar regions high in Earth’s atmosphere. Gases in Earth’s atmosphere are
excited by the electrically charged particles of the solar wind and glow producing curtains
of light, which bend and change as you watch.