Saturday, May 10, 2014

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.
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)
above 240
above 150
up to 240
up to 150
above 97
above 60
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