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What causes the beautiful northern lights?


Narrator: Welcome to Space Place Musings, where an expert answers questions from our Space Place museum partners across the nation. I'm Diane Fisher, of the New Millennium Program. Our expert is Dr. Marc Rayman, a scientist at the Jet Propulsion Laboratory.

Marc, some New Yorkers at the Lower Hudson Valley Challenger Center in Suffern wonder whether the aurora borealis can ever be seen in their area.

Rayman: Ah, the northern lights. I think they're so beautiful that I named my colorful pet iguana Aurora. The closer you live to the North Pole, the more likely you will see an aurora. The same cosmic spectacle is also visible near the South Pole, where it is called the aurora australis, or southern lights.

Narrator: But why are they visible only near the poles?

Rayman: It's because of Earth's magnetic field. Although the auroras look like Earth's own light show, the Sun is actually directing them. The Sun is always sending out a stream of electrically charged particles called the solar wind. When the particles get close to Earth, they start to feel the effect of Earth's strong magnetic field. Earth is like a giant magnet, with its field curving all around the planet and coming together into almost a funnel shape very near each of Earth's two poles. This magnetic field is called Earth's magnetosphere. It does a good job of protecting us from the solar wind, because it bends the paths of the charged particles from the Sun, in most cases steering them away from our planet. But the magnetic field also traps some of the particles and channels them down toward the poles, creating an enormous flow of electricity right into Earth's atmosphere.

Narrator: So why do the particles look like dancing curtains of colored light?

Rayman: When the particles in the solar wind collide with the thin air 100 km or more above the ground, the gases in the atmosphere give off light like the glowing gas in a neon light tube. Nitrogen may turn red, blue, and violet, and oxygen can color the sky red and green.

The closer you are to the poles, the more often you will be able to see auroras. But there have been times when the aurora borealis was visible as far south as Arizona. So whenever you're enjoying the beauty of a dark night sky, look to the north in case there is an aurora just then. In the southern hemisphere, the farther south you live, the better the aurora viewing.

Narrator: Are the auroras the same all the time?

Rayman: No. Our star has an 11-year cycle of activity, sometimes sending out more particles, sometimes less. Although auroras occur every year, the times of peak solar activity produce the most spectacular auroras. Sometimes, there are huge explosions on the Sun that fling tremendous numbers of charged particles into space. If these happen to be aimed at Earth, we can be treated to an especially marvelous display two or three days later, once the particles have raced across the space between the Sun and us.

Narrator: But what about Earth's magnetosphere? Does it ever change and affect the auroras and where they can be seen?

Rayman: Well, the interactions of the solar wind, Earth's magnetic field, and the upper atmosphere are very complex. We would really like to understand it all much better. As a matter of fact, as part of the New Millennium Program, the Space Technology 5 mission recently launched three tiny satellites that are studying the magnetosphere. Although their primary mission is to test their super miniaturized systems and advanced technologies, they are flying in highly elliptical orbits, dipping into and out of the magnetosphere and gathering data as they go.

Narrator: Do we know whether other planets have auroras?

Rayman: If they have magnetic fields and atmospheres, they do. My favorite planet, Jupiter, has an exceptionally strong and large magnetosphere. We have been able to see auroras at the poles of Jupiter, as well as Saturn, Uranus, and Neptune with the Hubble Space Telescope, Galileo, Cassini, Voyager, and other spacecraft.

Narrator: We're just about out of time, Marc. Where can someone explore auroras a little further?

Rayman: You have a cool article right here on The Space Place Web site, with a magnetic fields experiment that can be done at home. Folks can go to and search for "magnetic fields."

Narrator: That's a good place to start. Thank you, Marc. And thanks to you out there for stopping by to hear more Space Place Musings.