Sunspots

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

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 the 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.

Sunspots have been observed from the 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 the Earth's own field, or even 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.

The magnetic rope is mostly under the surface, but it forms a loop that emerges from the photosphere to form the two spots. 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.

 

Teacher Notes:

How have solar scientists formed models of their discoveries based on images, data, and observations of the Sun?

Models based on the data and images of the Sun are of special interest in science. Images and data from the instruments on satellites, allow scientists to form a type of model to learn about the dynamic and changing Sun.

(K-2) A model of something is different from the real thing but can be used to learn something about the real thing. A bar magnet, for instance, can represent the Sun's magnetic field.

(3-5) Geometric figures, number sequences, graphs, diagrams, sketches, number lines, maps, and stories can be used to represent objects, events, and processes in the real world, although such representations can never be exact in every detail.

(6-8) Models are often used to think about processes that happen too slowly, too quickly, or that are too vast to be changed deliberately, or that are potentially dangerous.

(9-12) The basic idea of mathematical modeling is to find a mathematical relationship that behaves in the same ways as the objects or processes under investigation. A mathematical model may give insight about how something really works or may fit observations very well without any intuitive meaning.

(9-12) The usefulness of a model can be tested by comparing its predictions to actual observations in the real world. But a close match does not necessarily mean that the model is the only "true" model or the only one that will work.

 

 

Science Nuggets:

1999...TRACE detects the magnetic structure of sunspots and other active regions and finds it a complex tangle of magnetic fields which explosively fill and empty of high-temperature plasma at speeds of thousands of kilometers per hour.

1998...SOHO studies probe the material below a sunspot and discover significant sound speed increases.

1997...SOHO discovers that the solar surface is covered by a 'magnetic carpet' of structures which follow the boundaries of surface granulation cells.