Before we can understand how auroras are made, we need to learn a few facts about our Earth and the space around it. There are many things in the space around the Earth that we can't see. Can you think of at least two of them? The first thing is what we need in order to breathe, our atmosphere. Our atmosphere is made up of several layers of gases surrounding the Earth. The outer-most layer is called the ionosphere, and is very important in the study of auroras. The second thing is a giant magnetic field. Our Earth's core is made up of metals which act like a giant magnet stuck in the center of the Earth. This creates a magnetic field around the Earth called the magnetosphere. If you've ever played with a magnet you've seen how a magnetic field can affect certain objects nearby. Our Earth's magnetosphere extends far out into space.

This picture shows how the magnetic field generated by the Earth's core is like the field of a bar magnet. Since we can't see the magnetosphere, we draw lines to represent it. Notice that it goes into and out of the Earth at the poles. These are the Earth's magnetic poles. The Earth's magnetic field varies in strength. Where the lines are closest together it is strongest. Where they are furthest apart it is weakest. Look at the picture. Can you tell where the magnetic field is the strongest? Where is it weakest?

But the Earth's magnetic field doesn't exist in empty space. The Sun has a magnetic field too. Also, atomic particles are constantly boiling off the Sun and moving outward at very high speeds. Together, the solar magnetic field and streaming particles are called the "solar wind." This wind is always pushing on the Earth's magnetic field, changing its shape. You change the shape of a soap bubble in a similar manner by blowing on its surface. This artist's illustration shows the shape of the Earth's magnetic field in the solar wind. The way the solar wind affects the Earth's magnetoshpere is an important part of what causes auroras.

Many things about how auroras happen are still unknown. However, scientists do know a lot about the events that lead to bright auroras. The auroral lights' fuel comes from the particles and energy of the solar wind, which is constantly changing. It takes 3 to 6 days for particles from the Sun to reach Earth. The number of particles and the intensity of the solar wind depends on how active the Sun is. Examples of solar activity include sunspots and solar flares. Because of the connection between solar activity and auroras, the more active the Sun is, the "bigger" the auroral events on Earth will be.

Energetic events on the Sun can turn the solar wind into an intense solar "gale" which injects large numbers of energetic particles in the Earth's magnetoshpere. The charged particles travel along the field lines with so much energy that they penetrate the ionosphere, where they hit gas atoms and molecules. These collisions give off energy that we see as colored light.

This historical graph shows how the sun and auroras might seem to be related.

What Makes Auroras Happen? Listen to David Stern of NASA's Goddard Space Center. To Listen to this clip you will need the RealAudio player.

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