If you have seen photographs of a solar eclipse, then you have probably noticed a bright halo around the Sun, called the corona. Sometimes parts of the corona appear to be missing. Logically, we call this area a coronal hole. Scientists believe that the solar wind, a million mile per hour gale that blows away from the Sun, originates in coronal holes. Unlike wind on Earth, the solar wind is a stream of ionized (electrically charged) particles speeding away from the Sun.
The Sun’s corona changes with sunspot activity. When there are more sunspots, the corona appears to be held closely to the Sun; when there are fewer sunspots, the corona streams out into space in a shape that resembles the spike on a warlike, peaked helmet called helmet streamers. While helmet streamers are long-lived, their demise often occurs abruptly through massive and powerful eruptions called coronal mass ejections (CMEs).
Artist’s conception of a coronal mass ejection moving away from the Sun toward Earth.
These huge clouds of hot solar gas and magnetic fields are often associated with solar flares. They can cause magnetic storms when they hit Earth’s magnetic field and dam- age human technological systems in space and on the ground. For example, in 1989, the Quebec province in Canada suffered an electrical blackout because many transformers were destroyed by a large magnetic storm. That one storm caused many millions of dollars worth of damage. A powerful solar flare erupted from the Sun about three days before the start of the storm at Earth. Even when the Sun is not too active, solar storms can cause problems. A magnetic storm on January 11, 1997 was blamed for the loss of a $270 million dollar AT&T communications satellite. This moderate storm was caused by a coronal mass ejection that erupted from the Sun even though there were no noticeable sunspots.
Student Guide, Activity 1: Features of the Sun © Space Science Institute, 1999. All Rights Reserved
Courtesy of the Los Alamos National Laboratory