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It's difficult to describe the aurora to someone who hasn't seen it. You can describe with a  mathematical precision the interaction of a single particle from a coronal mass ejection being trapped by the magnetosphere and then colliding with an atom of gas to give off a single photon.

You can describe the scale of  the 100 million of these collisions that are needed to make the aurora visible 100 miles below it on the ground.  But what no pen may describe and no brush reveal is the awesome power and incredible beauty of these dancing ribbons of green light at the very edge of space as they race from horizon to horizon as some unearthly hand plays a hose of light across the sky . 

The curtains of light that extend thousands of miles across the sky and flutter in the solar wind are more incredible in that they do so without a sound either from them or in accompaniment to them.  It all unfolds before you with only the sound of your own breathing.

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Aurora Safari information

More aurora information

The Aurora is caused by charged particles emitted by the sun hitting the earth's  magnetosphere and each particle giving off a tiny amount of light as it collides with the atoms of gas in the upper atmosphere.

The Earth is constantly buffeted by the solar wind which is emitted by the sun in all directions.  The solar wind usually reaches Earth within 9 seconds of leaving the sun but can also take up to three days!

The Earth's magnetosphere is critical in the formation of the auroras, it's the area of space controlled by our magnetic field. It forms an barrier in the path of the solar wind, causing it to be channeled around the earth in a teardrop shape. Geomagnetic storms that ignite auroras actually happen more often during the months around the equinoxes when the angle of the magnetosphere is in the best position with the sun.
 

Earth's magnetosphere waxes and wanes every six months. The solar wind speed is greatest around September and March when Earth lies at its highest heliographic latitude.  Add to this that these large magnetic storms are most common during the peak of the 11-year sunspot cycle, or during the 3 years after that peak.

There is never a guarantee of observing the aurora, even light cloud can shield it from the human observer and it will take over 100 million particles striking gas atoms to see it. 

The aurora is seen in the ring-shaped zone around both the north and south poles. It is occasionally nearer the equator, but only when exceptional magnetic storms move the visible ring sufficiently.  When the magnetic pole changes polarity, as it will again some time soon, then auroras will be seen all over the planet as the magnetic north pole moves to the south pole and many north poles exist during the transition.

The ultimate energy source of the aurora is undoubtedly the solar wind flowing past the Earth.

Both the magnetosphere and the solar wind consist of plasma, which can conduct electricity. It is well known that if two electric conductors are immersed in a magnetic field and one moves relative to the other, then an electric current will arise in that circuit, but the conductors can also be plasmas or other fluids.

In particular the solar wind and the magnetosphere are two electrically conducting fluids with such relative motion, and should be able to generate electric currents by "dynamo action", in the process also extracting energy from the flow of the solar wind.

Aurora Borealis

Dawn of the north wind

The image on the right was taken in the municipality of Muoino, 150km inside the arctic circle in Northern Finland. I have been there many times hunting aurora and during the last trip, after spending four nights in temperatures of -20c to -30c, I was rewarded with a huge aurora storm that lasted all of 15 minutes. Short but very intense. Three digital cameras (Nikon D70, D70s and a Canon20D kindly loaned to me by Canon UK) captured some amazing images as the storm ran from horizon to horizon. After 10 minutes the Li-on batteries started to go flat in the extreme low temperatures.  Changing batteries in the dark with huge mitts on while looking up adding to the drama of getting the shot.

The etymology of the nomenclature seems much later than the latin and Greek origins would suggest with it being as recently as the 17th century that the term Aurora Borealis was first used

In 1620, a Frenchman, Pierre Gassendi, saw the northern lights and named them after the Roman goddess, Aurora.  He also added the word 'borealis' for the Roman god of the north wind, Boreas.  From that point onwards the lights became known to scientists as the aurora borealis.

Aurora was a Roman deity, counterpart of the Greek mythological Titan goddess of the dawn  Eos.  Eos would rise from her home at the edge of Oceanus, the sea that surrounded the world, to open the gates for her brother Helios to ride his chariot across the sky each day.  Aurora's sister was Selene, the moon.  She had many husbands and one of her sons was Boreas, the north wind.  The literal translation of Aurora Borealis is therefore  "Dawn of the North wind."

 However! Boreas was a Greek deity, not Roman. The roman deities for the winds were "Venti" the north wind, Aquilo or Aquilon, sometimes Septentrio was used to mean Northern wind.  It is still widely accepted that the term comes from Roman mythology.

The Finnish word for Aurora translates as Firefoxes, and whistling will make them appear. I did a lot of whistling on this last trip.

The Etruscan name for the goddess Aurora was Thesant

From Shakespeare's Romeo and Juliet;

 But all so soon as the all-cheering sun
    Should in the furthest east begin to draw
    The shady curtains from Aurora's bed,
    Away from the light steals home my heavy son...

The collective noun for polar bears is an aurora of Polar bears