In my class I have hanging from the ceiling on a string a pencil, parallel with the ground, with some magnets taped to it. The carefully ordered magnets force the pencil to point north. This homemade compass is a simple, but elegant, everyday display of our planet's magnetic field.

And what a field it is!

Our magnetic field reveals to us what is going on down below our feet, helps us find our way on the surface, and protects us from destruction above. How?

Through some complicated physics, it has been shown that a magnetic field can arise from a rotating, conducting fluid. Meaning, if a planet has a sphere of liquid iron down below the surface, the rotation of that planet can cause the liquid to throw a protective magnetic shield around the planet. The field is similar in shape to that taken by iron filings around a bar magnet, like we all saw in elementary school.

We believe that way down below, at the center of planet earth, we have an "inner core" made of very hot - but solid - iron and nickel. But surrounding that we have a molten, swirling "outer core" of liquid nickel and iron, perfect conditions for a magnetic field.

On our surface we can take advantage of this magnetic field with a compass, which has a magnetized pointer that lines up with our magnetic field and allows us to find magnetic north (which is not exactly true north, but close). This has allowed people for centuries to find their way around this planet, and has saved many a lost soul.

Way above us, our all-encompassing magnetic field interacts with pesky charged particles. So what? So this...

The sun bathes us in a wind of charged particles called - surprise - the solar winds. Composed of mainly protons and electrons, this wind travels at hundreds of miles per second.

But instead of those bothersome particles blasting into us and wreaking havoc on our atmosphere - especially on poor water vapor which it can strip from a planet - our magnetic field steps in and calmly says, "Wait a minute, here."

The laws of nature ensure that our magnetic field will deflect the charged wind around earth and by us, like a sailing ship forces the waters aside and around.

Some of the particles do manage to sneak in through the weaker areas, around the earth's poles. As they crash into the atmosphere they light up the skies in beautiful Northern and Southern Lights.

If you ever see the Lights, or just play with a child's compass, pause. You are witnessing the effects of a remarkable planetary phenomenon.