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1 http://beyondpenguins.nsdl.org/ Issue Three: Patterns: Day, , and Seasons (May 2008)

The Aurora: Fire in the by Stephen Whitt

The northern (or the southern lights, if you’re from the ) are eerie, multicolored streaks and shapes that appear in the , as if from nowhere. To find out where they come from, we’ll have to take a little trip. Are you ready?

Imagine you are on the . The Sun’s temperature is much too hot for anything alive. But you aren’t alive. You are a tiny particle so small that you can’t be seen in even the most powerful microscope.

Now imagine that you are hurled away from the Sun. Believe it or not, this actually happens all the time. The Sun sends out streams of tiny particles every second. We call this stream the solar .

Heat causes the . The Sun is so hot that particles fly off its surface, a little like steam rising from a hot bowl of soup.

Imagine you’re a part of this solar wind. You’re flying away from the Sun faster than the fastest spaceship. Directly ahead of you is , a pretty blue- white ball. You’re moving fast, but Earth is still far away. It takes you a little over four days to make the trip to Earth.

What happens when you reach Earth? To find out, let’s leave the solar wind for a moment and travel back in time, to meet a scientist and explorer named .

Kristian Birkeland wanted to understand the aurora (another name for the northern and southern lights). The mysterious was often seen near the Flesch-Kincaid RL = 5.2

Copyright May 2008 - The Ohio State University. Funded by the National Science Foundation. This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License.

2 http://beyondpenguins.nsdl.org/ Issue Three: Polar Patterns: Day, Night, and Seasons (May 2008) and South Poles. It wasn’t usually seen closer to the . People described the light as a “fire in the sky.” But what could it be?

Birkeland had an idea. He knew that Earth was a giant magnet. Like all magnets, Earth has a and a . Birkeland led an expedition to to measure Earth’s .

He found that near the North Pole, the magnetic field lines don’t run along the Earth’s surface, the way they do near the equator. Instead, the field lines go almost straight up and down. What could that mean?

Think of the Earth as a magnet. Near the middle of the magnet (where the Earth’s equator would be) the lines of force run right alongside the magnet. But near the North and South Poles, the lines run almost straight into the ends of the magnet.

Kristian Birkeland now knew more about the Earth’s magnetic field. But he still didn’t know what caused the aurora. How were the two things related?

To understand how these things are related, you need to know a little about electricity.

Have you ever rubbed your feet across the carpet and then touched something made of metal? If you have, you’ve felt a shock! You build up an electric charge when you rub your feet on the carpet. The charge moves from your finger to the metal when you touch it. This movement is what causes the shock.

The particles from the Sun also carry an electric charge. But how does this charge create the aurora?

Flesch-Kincaid RL = 5.2

Copyright May 2008 - The Ohio State University. Funded by the National Science Foundation. This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License.

3 http://beyondpenguins.nsdl.org/ Issue Three: Polar Patterns: Day, Night, and Seasons (May 2008)

Here’s the key idea. Electricity and magnets affect each other. Watch a compass during a thunderstorm. You’ll see the magnet inside the compass (what we call the needle) move every time lightning flashes across the sky.

Now we know that electricity affects magnets. But do magnets affect electricity? Yes! Kristian Birkeland showed how by building a magnetic model of the Earth. He found that the charged particles traveled along the magnetic field lines. They moved away from the equator and followed the lines to the North and South Poles.

Now let’s go back to those real charged particles flying off the Sun. Just like in the model, the charged particles are pushed by the Earth’s magnetic field toward the poles. Once they get there, they follow the magnetic field lines down toward the ground.

Before the charged particles can get to the ground, though, they smash into air molecules. The collisions make the molecules glow with beautiful, bright colors – green, pink, and red. This is the aurora, light created by tiny particles from the Sun smashing into the Earth’s atmosphere at the end of a four-day journey through space. That’s quite a trip!

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Glossary aurora - another name for the northern or southern lights compass - a tool that measures Earth’s magnetic field and is used to find directions

Flesch-Kincaid RL = 5.2

Copyright May 2008 - The Ohio State University. Funded by the National Science Foundation. This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License.

4 http://beyondpenguins.nsdl.org/ Issue Three: Polar Patterns: Day, Night, and Seasons (May 2008) electric charge – a measure of the extra positive or negative particles that an object has expedition - a trip made by a group of people for a particular purpose magnetic field – the space all around a magnet where the force of the magnet can act molecules – a grouping of two or more atoms joined together particles – tiny pieces of matter that make up solids, liquids, and gases solar wind - electrically charged particles that come from the sun

Flesch-Kincaid RL = 5.2

Copyright May 2008 - The Ohio State University. Funded by the National Science Foundation. This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License.