WHAT ARE NORTHERN LIGHTS?
The bright dancing lights of the aurora are actually collisions between electrically charged particles from the sun that enter the earth’s atmosphere. The lights are seen above the magnetic poles of the northern and southern hemispheres. They are known as ‘Aurora borealis’ in the north and ‘Aurora australis’ in the south..
Auroral displays appear in many colours although pale green and pink are the most common. Shades of red, yellow, green, blue, and violet have been reported. The lights appear in many forms from patches or scattered clouds of light to streamers, arcs, rippling curtains or shooting rays that light up the sky with an eerie glow.
WHAT CAUSES THE NORTHERN LIGHTS?
The Northern Lights are actually the result of collisions between gaseous particles in the Earth’s atmosphere with charged particles released from the sun’s atmosphere. Variations in colour are due to the type of gas particles that are colliding. The most common auroral color, a pale yellowish-green, is produced by oxygen molecules located about 60 miles above the earth. Rare, all-red auroras are produced by high-altitude oxygen, at heights of up to 200 miles. Nitrogen produces blue or purplish-red aurora.
The connection between the Northern Lights and sunspot activity has been suspected since about 1880. Thanks to research conducted since the 1950’s, we now know that electrons and protons from the sun are blown towards the earth on the ‘solar wind’. (Note: 1957-58 was International Geophysical Year and the atmosphere was studied extensively with balloons, radar, rockets and satellites. Rocket research is still conducted by scientists at Poker Flats, a facility under the direction of the University of Alaska at Fairbanks – see web page http://www.gi.alaska.edu/
The temperature above the surface of the sun is millions of degrees Celsius. At this temperature, collisions between gas molecules are frequent and explosive. Free electrons and protons are thrown from the sun’s atmosphere by the rotation of the sun and escape through holes in the magnetic field. Blown towards the earth by the solar wind, the charged particles are largely deflected by the earth’s magnetic field. However, the earth’s magnetic field is weaker at either pole and therefore some particles enter the earth’s atmosphere and collide with gas particles. These collisions emit light that we perceive as the dancing lights of the north (and the south).
The lights of the Aurora generally extend from 80 kilometres (50 miles) to as high as 640 kilometres (400 miles) above the earth’s surface.