Looking at the Northern Lights

Aurora BorealisThe Aurora Borealis—that mysterious shimmer of light appearing sometimes in the night sky—is a great thing to contemplate now during Hanukkah, our Festival of Lights, and so close to the Winter Solstice. You can’t even plan to see the Aurora, this huge, otherworldly phenomenon, one of the strangest of light events on earth. You just have to show up where it might be seen and hope one will reveal itself.

What is the Aurora Borealis, anyway? It was named for Aurora, the Roman goddess of dawn, and for Boreas, the north wind, in the 17th century, and often just called the Northern Lights.

Before scientists teased out the secrets of the Northern Lights, the Kwakiutl and Tlingit people of Alaska interpreted them as the dancing of human spirits. The Inuit people of Labrador identified them as the torches held by spirits from the true heavens beyond the sky, meant to lead newly arrived spirits on the right pathway. The Algonquin Indians said that they were the reflection of fires built by the Creator, who retired to the north after he finished his work, kept burning to remind the people that he still thinks of them.

The story told by scientists is just as incredible. Our sun throws off constant small storms of plasma—masses of electrified gas ejected out from its surface. These fly out in all directions on the solar wind. When they get near enough to the earth, they slide across our magnetosphere—the giant electromagnetic body that surrounds us, basically shielding us from getting too much radiation from the sun and the cosmos.

Earth's magnetosphere absorbing solar plasma
Earth’s magnetosphere absorbing solar plasma, still from animation at http://wimp.com/borealisaurora/

Some of the plasma is pulled in and sucked toward the north and south poles, where it interacts with elements in the stratosphere. Here’s a great animation showing this process.

This interaction of particles of sun and earth creates the Aurora Borealis, as well as the Aurora Australis in the southern hemisphere. A green light show, the most common, means that oxygen particles have been more excited by the flux of free electrons and positive ions, at an altitude of up to 150 miles. The rarely appearing red Aurora means it’s happening even higher than that. Blue or violet light shows reveal the involvement of nitrogen particles at a lower altitude. Sometimes the Aurora appears as undulating curtains, sometimes as swirling lines, or merely a soft allover glow. We now have numerous images, and even videos taken from space, showing how globe-spanning a single event can be.

Aurora seen from space
Aurora seen from space, Wikimedia Commons

Have you seen the northern lights? I haven’t, but I hope I’ll be lucky enough to see them with my own eyes someday. It will be a chance for an up-close encounter with an off-world astrophysical effect, without the need for filters or lenses—a direct experience of the vast electromagnetic environment around us as it briefly drops into the visible realm, to become a stunning spectacle of light in the darkness.

 

 

 

 

 

 

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