A video clip of a sunspot moving across the surface of the Sun. Sunspots can be up to several times larger than the diameter of the Earth. (Click to launch movie.)

Believe it or not, although you cannot hold a piece of the Sun in your hand, you can explore a model of the forces that control most of its active surface. The Sun has a magnetic personality.

Magnetic Mystery
For over 100 years, astronomers have known from direct observations that the Sun's surface has a magnetic field that is about twice as strong as Earth's, but spread out over 10,000 times the area. We don't exactly know where it comes from. It may have been left over from the interstellar cloud that created the Sun over 4.5 billion years ago. Some astronomers think it is actually generated by the Sun itself.

Over all, the Sun's field looks a lot like a bar magnet. It has a north and south polarity as all magnets do. Much of its shape can be seen during a total solar eclipse as it leaves an imprint on the Sun's outer gases, just like iron filings outline the field of a bar magnet. But there is more to the Sun's magnetism than what you might find by just looking at a bar magnet.

While Sunspots are only moderately cooler they are considerably darker as this image from the Big Bear Observatory shows.

Sunspots have been observed from Earth by ancient Chinese astronomers for over 4000 years, but only in the last 200 years have astronomers begun to figure out just what they are. Sunspots are actually intense concentrations of magnetic energy nearly 4000 times stronger than Earth's own field, stronger than the rest of the Sun's. Somewhere within the Sun's convective zone, perhaps where it bumps up against the deeper radiative zone, conditions are just right for creating jet streams of flowing currents. These currents create ropes of magnetism, which can get concentrated by convective gas flows. When they reach the surface, they pop through and form pairs of sunspots.

Opposites Attract
Sunspots have a tendency to occur in pairs or more complex groups. When they occur in pairs, one sunspot always has the opposite magnetic polarity of the other, and they usually follow each other around the surface of the rotating Sun. This is why the magnetic field of a sunspot pair often looks like a bar magnet, although on a scale billions of times larger than in your classroom. The gases in the centers of sunspots have temperatures of about 3000 Centigrade. They appear dark because of their contrast with the rest of the solar surface which is at a temperature of about 5700 Centigrade.

Magnetic "loops" as seen here demonstrate the intense magnetism exhibited near sunspot areas. This video was taken by the NASA TRACE spacecraft. (Click to launch movie.)

Find out more about the Sun-Earth Connection at the Sun-Earth Connection Education Forum Web site.

Text adapted from the Sun-Earth Connection Tutorial courtesy of NASA, originally written by Dr. Sten Odenwald. Images and videos courtesy of NASA unless otherwised noted.