This is Science Friday. I'm Iroflato, wishing a Merry Christmas to those of you celebrating.

The winter holidays are a time for colorful lights. And if you live in the northern latitudes,

you may have been treated to nature's own light show. I'm talking about the Aurora Borealis.

Never having seen the northern lights myself, perhaps now I'll get to see

the glowing green in the sky normally found closer to the poles. They've been spotted as far

south as Michigan and Ohio. Syphre's Charles Berkwist has more. The aurora forms when streams

have charged particles from the solar wind interact with gases in our upper atmosphere.

It works sort of like a neon sign. The charged particles excite the gas, making it emit light.

Don Hapton is a research associate professor in the Geophysical Institute of the University of Alaska

in Fairbanks. He studies the Aurora, including by firing rockets

up into it. Welcome to Science Friday. Good morning. So people say charged particles, hitting gases.

What sort of particles are we talking about and what sort of gases? The solar wind is primarily

electrons and protons because the sun is mostly just hydrogen.

And so when you break those apart, that's what you get.

Those are sort of captured in our Earth's magnetic field.

And so the particles that create the light that we see typically with the aurora are primarily

electrons that are accelerated down by electric fields and the magnetosphere, come down and,

as you say,

bump into the upper atmospheric gas molecules and atoms and create the light.

And generally it's a sort of greenish glow, but there are different colors too.

What makes the difference in colors?

Is it a difference in the particles or a difference in the gases that it's hitting?

...