For many years people have wondered just what the Northern Lights were.

People believe that they are elementary particle physics, superstition, mythology and fairy tales. The Northern Lights or Auroras, are nature’s light shows. They have filled people with wondered and have inspired artists, and they have also frightened people to think that the end is near. More exact explanations of these phenomenon could not be given until modern particle physics were developed, and knowledge about the Earth’s magnetosphere has been based on measurements from satellites.

The Sun throws out particles, from its surface, far out into space.

These particles are called “Solar Winds,” and cause the Northern lights.

What was once hydrogen becomes a gas of free electrons and protons called plasma. This plasma escapes from the Sun’s atmosphere through a hole in the Sun’s magnetic field. As they escape, they are thrown out by the rotation of the sun in a continuous spiral. This is called the garden-hose effect. The names comes from the pattern of water droplets that form if we were to swing a hose around and around, above our heads.

After about two to five days traveling through space, the plasma (solar winds) reaches the earth’s magnetic field, forcing it on the day light side of the earth, and stretches into a “tail” on the night side. A few particles penetrate down to earth along the lines of the magnetic field and enter the “tail” which stretches out into a long cylinder. It is as if the earth’s magnetic field created a tunnel in the plasma current from the solar winds.

The magnetic tail is divided into two by a sheet of plasma. The magnetic field lines from the earth’s north and South Pole stretch out in their halves, so that the fields are in opposition. The electrons and protons in each half of the plasma rotate in the opposite direction forming a huge “dynamo” with the positive pole on the side of the plasma sheet facing dawn and the negative pole facing evening. The current of charged particles drives the “dynamo” between the two poles.

When the northern lights break out, this is what happens. The solar winds strengthen and the magnetic tail becomes unstable. Charged particles move inward towards the center of the tail and cause it to increase in length and to taper. The particles draw the magnetic field lines toward the center where they meet causing a magnetic “short-circuit” about fifteen times the earth’s radius above the earth on the night side. This happens at the “dynamo’s” outer circuit.

Most of the northern lights we see form in electrons and move into the ionosphere. The mechanism by which their kinetic energy is converted to visible light is called the quantum leap. To explain this mechanism, imagine a hydrogen atom consisting of a single positive proton nucleus around which spins a single electron at a set distances. Normally, the electron is in an orbit as close to the proton as possible. In a state like this, the hydrogen atom a minimum energy. There are other possible orbits further away from the nucleus in which the electron can spin. When a free electron collides with a hydrogen electron at a high speed, it releases energy. Because of this, the spinning electron moves into another, higher energy orbit further out from the nucleus. It now contains more potential energy, but is unstable and unable to keep this energy. It returns to its original orbit, releasing the extra energy as a photon of light. Billions of these quantum leaps that keep occurring create the Northern lights.

The particles that come down from the magnetic tail reach the earth in a belt called the northern lights oval. This belt is wider on the night side of the earth than on the day side and is centered on the magnetic pole, while the earth revolves around the geographic poles. The width of the belt on the night side is up to 600 km.

In the old days, the weather forecast was sometimes based on the northern lights.

However, they were often inconsistent. In Labrador, colored lights meant good weather opposed to in Greenland they were a sign of storms. Even in the last century, you could read in an encyclopedia that the northern lights and thundery weather were the result of the same phenomenon, but with different forms of electrical discharge. In North Norway, the northern lights were often associated with cold weather.

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Between 1645 and 1715, there was not a lot of sunspot activity and therefore little northern lights activity. This period is called the Maunder minimum, after the leader of the Greenwich Observatory in England who was the first to document this low activity. The northern lights oval was then in a position that the northern lights should have been visible, but the sun was less active and the northern lights failed to appear. During periods like this, the climate on earth generally tends to be colder and the Maunder minimum corresponds with what is now known with as the Scandinavian “little iceage.” Since then, sunspot activity has increased and reached a maximum in 1991. This was the largest maximum in 300 years with more solar energy release, greater sunspot activity and more northern lights.

C h a r g e d p a r t i c l e s i n s p a c e t h a t g e t n e a r t h e E a r t h ' s m a g n e t i c f i e l d c a n g e t i n a n d t r a p p e d .

O n c e t h e y a r e t r a p p e d , t h e p a r t i c l e s s p i r a l d o w n t h e m a g n e t i c f i e l d l i n e t o w a r d s t h e E a r t h ' s m a g n e t i c p o l e s .

I t i s h e r e a t t h e p o l e s w h e r e t h e p a r t i c l e s h i t t h e g a s e s i n t h e E a r t h ' s a t m o s p h e r e .

T h e s e c o l l i s i o n s g i v e o f e n e r g y t h a t w e s e e a s c o l o r e d l i g h t .

F o r a u r o r a s t o h a p p e n , p a r t i c l e s m u s t b e t r a p p e d b y t h e E a r t h ' s m a g n e t o s p h e r e .

September and March are the most frequent months for auroras and January and July the least likely. Most of the solar activity comes from regions of the sun outside the solar equatorial band +/- 10 degrees to either side of the solar equator. The Earth in it’s orbit is inside this equatorial band during January and July, and when it is at it’s maximum in September and March, the Earth is in the zone of solar activity

The gases in the Earth’s atmosphere determine the auroral lights’ colors. In the ionosphere, where the collisions are taking place, incoming solar particles collide with oxygen and nitrogen gases. Oxygen atoms give off green and red light. Nitrogen atoms give off red light. Some blue and violet light is also given off, but it is difficult for our eyes to see it.

No two auroras are alike. Auroras start off low on the horizon, then a faint glow of light appears. Slowly, an arch of light lazily stretches across the sky.

Bands of light layer on top of each other reaching higher into the sky. The lights begin to blend together. The layers seem to drip into each other as waves move slowly across the sky. The lights form a giant curtain in the sky that slowly waves as if a gentle breeze were blowing. At the bottom of the curtain, waves ripple across the sky curling and bending in the imaginary wind.

EARTH'S AURORAS MAKE RARE JOINT APPEARANCE

• • Scientists using NASA's Polar spacecraft have captured the first-ever movie of auroras dancing simultaneously around both of Earth's polar regions. During a space weather storm on October 22, Polar's Visible Imaging System observed the

aurora borealis

and

aurora australis

(northern and southern lights) expanding and brightening in parallel at opposite ends of the world. The images confirm the three century old theory that auroras in the northern and southern hemispheres are nearly mirror images -- conjugates - of each other.

"This is the first time that we have seen both auroral ovals simultaneously with such clarity," says Dr. Nicola Fox, the science operations manager for the Polar spacecraft, based at NASA Goddard Space Flight Center. "With these images, we have the ability to see the dynamics of conjugate auroras."