THE NORTHERN LIGHTS by PORTER JOHNSON


The Northern Lights
Porter Johnson

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The Northern Lights are nature's light show, with quantum leaps in oxygen and nitrogen atoms in an impressive display of luminous curtains and rays that dance above the tundra.  They involve the interplay of elementary particle physics with superstition, mythology, and fairy tales.  Their fickle hues, their radiance, and their grandeur have filled people with wonder and inspired artists; they have frightened people to think that the end is at hand.  More exact explanations could not be given until modern physics was developed, and knowledge about the earth's magnetosphere was obtained from measurements with artificial satellites.

We pose certain questions pertaining to the Northern Lights, with relevant information.


Questions Concerning the Northern Lights


What are the Northern Lights?

The aurora was named after the Roman goddess of dawn by a 17th Century scientist named Pierre Gassend. It was long thought to be produced by sunlight reflected from polar snow and ice, or refracted light much like rainbows.  Benjamin Franklin, Aristotle, Descartes, Edmund Halley, Goethe, and Henry Cavendish have all been fascinated by their array in the night sky, and have all written papers about them.

The simplest explanation for the Northern Lights is that, just as the gas in a Neon light glows when charged with electricity, so the gas in the atmosphere glows with specific colors when charged with electric particles from the sun.

In days of old, weather was sometimes forecast by the Northern Lights, but the predictions were often contradictory.  Between 1645 and 1715, there was little sunspot activity and therefore little Northern Lights activity.  This period is called the Maunder minimum, which corresponds to the Scandinavian Little Ice Age.

For additional discussion of an interesting connection in the Northern Lights with climate, see the website
http://www.bbc.co.uk/weather/features/understanding/northernlights.shtml

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Where are the Northern Lights seen?

In the northern hemisphere, prime viewing locations include Fairbanks Alaska and many locations in eastern Canada.  In Europe, Iceland and northern Scandinavia see the most aurora.  In the southern hemisphere, the aurora occurs in uninhabited regions, making the sighting of aurora australis, the southern lights, much rarer than the northern lights, aurora borealis.

For more information see the website
http://www.swpc.noaa.gov/pmap/pmapN.html

Incidentally, any planet with a magnetic field will have the aurora.  Voyager saw them on Jupiter and Saturn.

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What is the energy source of this phenomenon?

Although seen here on earth, an aurora starts at the center of the solar system.  The sun is constantly blowing out a stream of electrons and protons, called the Solar Wind.  After about three days those particles get near earth and hit its magnetic field.  The earth's magnetic field can be visualized as coming out of the ground at the south pole, going around the earth from south to north, and then going back in at the north pole.  The particles that hit that magnetic field want to 'slide down' the field to the poles, eventually hitting the earth's atmosphere, and they may be trapped in the Van Allen belts. When they hit the air, these fast-moving particles knock loose electrons from atoms in the atmosphere.  After a time the free electrons get back to atoms, and the atoms emit light.  When this happens to many atoms, you get the aurora. The power consumed in an aurora display is much greater than the power usage in the United States.

The power in the aurora depends upon the strength of the Solar Wind, and can become quite strong during an intense solar storm.  The earth's magnetic field is disrupted, and currents can be induced in power lines.  There have been power blackouts during strong solar activity, and orbiting satellites are also in danger.

For more details see the website
http://www.badastronomy.com/mad/1996/aurora.html.

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What determines the colors of the Northern Lights?

The most common color, a pale green, arises when electrons collide with oxygen atoms below an altitude of 400 km.  More elevated encounters of electrons with oxygen may also yield a red glow.  Nitrogen molecules near the bottom of the ionosphere sometimes produce red light, but usually with less intensity. Charged nitrogen molecules can emit deep violet light, which is difficult to see.

Upon occasion there is blue light coming from hydrogen atoms, which is indicative of an especially high concentration of protons in the Van Allen belts, since hydrogen in the ionosphere is very rare.

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Does the aurora make sounds?

This question is always good for a lively discussion among residents of the north.  So far, attempts to record sound during aurora have failed to produce any proof that sounds exist, but it is hard to ignore the numerous reports that go back centuries.

For additional discussion, see the website
http://www.damninteresting.com/the-sound-of-the-aurora

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What is not understood about the Northern Lights?

Nobody knows what processes produce the many forms of the Northern Lights---the rays and arcs, the folds and filaments, the spirals and patches, the diffuse, pulsating  veils and curtains. The mechanism for energy transfer to particles [electrons and some protons] in the Van Allen belts, which would cause them to move in  spiral orbits that wrap around magnetic field lines,  and to then to tunnel into the atmosphere at the poles, is also very obscure.

It also is not clear what causes auroral sub-storms---bright, dynamical global displays with spectacular visual effects.  Despite decades of study, auroral prediction involves plasma physics, atmospheric science, and lots of "voodoo".  Our understanding of "space weather" is understood quite poorly today, as was "terrestrial weather" a century ago.

On October 1998 a gap was observed in the aurora borealis, as seen by a spacecraft orbiting over the North Pole.  The source of this gap in the aurora is not known.

For more details see the website
http://science.nasa.gov/newhome/headlines/ast16oct98_1.htm.

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Can the Northern Lights be produced by man?

Auroras occur in the upper atmosphere under the right conditions, but researchers can also create artificial auroras to learn about the atmosphere.  In the 3 July 2000 issue of the journal Physical Review Letters, a team describes a new way of using the aurora to illuminate the lower ionosphere.  They transmitted powerful radio waves upward at night and took pictures as low-lying clouds of ionized atoms glowed green in response.  The technique will allow more detailed observations of a turbulent and poorly understood atmospheric layer that affects satellite and radio communications.

"The Structure of Electromagnetic Wave-Induced 557.7-nm Emission Associated with a Sporadic-E Event over Arecibo", L. M. Kagan,  M. C. Kelley,  F. Garcia,  P. A. Bernhardt,  F. T. Djuth,  M. P. Sulzer, and C. A. Tepley, Phys. Rev. Lett. 85, 218 

If our eyes were more sensitive, we would see a dim red and green glow in the night sky from excited nitrogen and oxygen hundreds of kilometers up.

See also the website
http://focus.aps.org/story/v5/st30

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What about poems and stories involving the Northern Lights?

Northern cultures have created a rich folklore surrounding aurora.  One of the earliest known written references is in the Old Testament, in which it is described as "fire raining down from heaven".  The following description in the vision of the glory by the Prophet-Priest Ezekiel is surely based upon his observations of the aurora -- very rare at temperate latitudes: 

"And I looked, and, behold, a whirlwind came out of the north, a great cloud, and a fire infolding itself, and a brightness was about it, and out of the midst thereof as the colour of amber, out of the midst of the sky."

- Ezekiel: Chapter I, verse 4
[Authorized King James Version]

 The Romans called it "blood rain", the Chinese "candle dragon", and Eurasian tribes  "wind light".  On several occasions, the aurora struck fear in the peoples of Italy and France.  Sometimes when the aurora is large and extends that far south, it is a rich dark red color.  The people of Europe associated it with blood and battle and saw it as an omen of disaster.  The East Greenland Eskimos believed the aurora are the students of children who died at birth.  Various cultures believed aurora are the dead playing a ball game.  The only Eskimo group that considered the Aurora an evil thing were the Point Barrow Eskimos, who believed it so deeply that they used to carry knives to keep it away.  The T'lingits and Eyak Indians of Southeastern Alaska consider them a sure sign of impending battle, and that someone will be killed when they occur. A typical account is described as follows in a recent  Discover Magazine article:

"Streaks of light toss about with abandon.  Suddenly, for a second, all light melts away and the sky is full of darkness.  Just as quickly, the lights blossom again in pulsating waves and arcs, and in undulating movements across the whole heavens, sometimes stabbing the ends of their folds toward the earth, dripping with the green of grass and the red of blood."

The Norwegian Poet Knut Hamsun compared the aurora to a heavenly feast in the poem Snow:

"Flaming lights on the sky
a night of northern lights
A wedding is going on up there
among the crowd of stars
The Moon is rising
a god among sparkling goddesses."

For more details see these websites:

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What about Reference Materials?

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