Q Why do northern and southern lights appear only at North and South poles?

— Sam Franzen

A Marian Mateling, research assistant in the department of atmospheric and oceanic sciences at the University of Wisconsin-Madison:

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 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 of this activity is centered on 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 on the geomagnetic poles.

They 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 particles of light.

Blue Sky Science is a collaboration of the Wisconsin State Journal and the Morgridge Institute for Research.


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