A Charged Sky

Ancient peoples had a more vivid view of the night sky than we have. Our forebearers created colorful mythologies to explain the light shows known as Auroras, but we hemispherically-centric people in the northern hemisphere call the Northern Lights.

Northern Lights over Lyngen fjord, March 2012.

Auroras occur because of solar winds. Solar winds are highly charged electrons blown from the Sun toward the Earth. Streams of charged particles, called plasma, escape the Sun's gravity because of their high energy (1.5 to 10 KeV).

“A man is a very small thing, and the night is very large and full of wonders.”
― Lord Dunsany

Solar winds flow at supersonic speeds outward from the Sun covering great distances and creating geomagnetic storms in the Earth's magnetosphere.
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Depiction of solar wind particles interacting with Earth's magnetosphere.

When the highly charged electrons enter the Earth's upper atmosphere they encounter oxygen and nitrogen at various altitudes. Color in Northern Lights is determined by whether oxygen or nitrogen atoms are struck first and at what altitude.

Color	Gas	Alt. (km)	Alt. (miles)
Red	Oxygen	above 240	above 150
Green	Oxygen	up to 240	up to 150
Purple	Nitrogen	above 97	above 60
Blue	Nitrogen	up to 97	up to 60

Shifting combinations of charged particles encountering atmospheric gases at various altitudes make the Northern Lights undulate and dance in the night sky.

The core and the surface
Are essentially the same,
Words make them seem different
Only to express appearance.
If name be needed, wonder names them both:
From wonder into wonder
Existence opens.
― Lao Tzu, translated by Witter Bynner

REFERENCES

• Aurora, Wikipedia.
• Northern Lights Mythology & Science, GrokEarth, 24 March 2012.
• Solar Wind, Wikipedia.

Northern Lights Mythology & Science

The Northern Lights are a spectacle. Knowing the mythology and science of auroras enhances the poetic quality of nature's light show. Understanding something so grand does little to diminish one's awe.

Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.
~ John Lubbock

Mythology

• The Algonquins of North America believed Nanabozho, after creating earth, went to the far north to build great fires reflecting southward as an expression of lasting love.
• The Finnish word for the northern lights translates to Fox Fires originating from a Finnish fable. In the fable, the lights were caused by a fox sweeping his tail across the snow spraying it into the sky.
• The Saami, indigenous arctic people, believed the lights to be blazing fires from the souls of the departed and to disrespect the fires would lead to bad fortune.

Geophysics

There wasn't a scientific rationalization of the Northern Lights until French geophysicist Jean-Jacques d'Ortous de Mairan linked auroras to solar activity in 1774.

An aurora is a display of light in the sky prevalent in the high latitudes. The light emanates from the collision of energetic charged particles with atoms in the high altitude atmosphere. The charged particles originate in the magnetosphere and from solar wind. The Earth's magnetic field draws the particles into the atmosphere. During a geomagnetic storm, the visible auroral zone expands into lower latitudes.

NASA Crew Earth Observations uploaded the following video sequence of an aurora over the Great Lakes and Canada.

The video was made by the crew of Expedition 30 on board the International Space Station. The video sequence was made on January 25, 2012 from 09:27:08 to 09:32:16 GMT, as the Space Station passed from northwestern Wisconsin to southeastern Quebec, near the Gulf of St. Lawrence.