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Blue Sky Science: Why do the northern and southern lights only appear near the poles?

Sam Franzen

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Why do the northern and southern lights only appear near the poles?

The formation of the northern and southern lights—known as aurora borealis and aurora australis—begins with solar flares from the sun. The solar flares eject groups of electrons from the sun that act as a wind and flow toward the Earth.

When the solar wind of electrons reaches the planet, they first encounter Earth’s magnetic field, referred to as the geomagnetic field. This magnetic field will deflect the electrons. With this deflection, the electrons move around the planet and hit near the polar regions where the magnetic field is weakest.

That’s how the daytime auroras occur, when electrons hit the sun-facing magnetic field and are deflected to the poles.

But the solar wind doesn’t stop when it first encounters the planet. It will continue to move to the other side of Earth, the side facing away from the sun, and reach the back side of our magnetic field.

When it hits the back side of Earth’s magnetic field, electrons are again drawn in toward the poles, creating the nighttime auroras.

All this activity is centered around the geomagnetic poles, which are about 10 degrees different in latitude than the regular North and South Poles we think of.

Views from space show the auroras as rings of light that are centered around the geomagnetic poles. The appear to those on Earth as curtains of light due to the structure of the magnetic fields.

The most common colors seen are green and blue, but the auroras can also show pink and orange hues depending on the interactions of photons, particles of light.

About Blue Sky Science

Blue Sky Science is a collaboration of the Wisconsin State Journal and the Morgridge Institute for Research. The questions are primarily posed by visitors attending Discovery Building events.

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