A Cold Night in February ...

Was made more inviting by a brilliant display of Northern Lights, 100 km above Edmonton!  This shimmering curtain of light originates when charged particles from the sun collide with Oxygen and Nitrogen atoms and molecules in the earth's upper atmosphere.  The rapid motion sometimes seen in the aurora is actually an "illusion".  The gases in the atmosphere are not moving, rather it is charge moving rapidly back and forth causing the gases to glow and giving the impression of motion.  In its simplest terms, northern lights arise from immense electrical discharges into the upper atmosphere.
A gentle green arch begins to form over downtown Edmonton early in a February evening, 1993.  The green colour is due to Oxygen atoms being excited between 100 km and 150 km above the earth.
As the magnetic field lines of the earth "swish back and forth they carry the charged particles with them giving the allusion of a moving aurora. Finally the aurora forms elaborate folds and sheets.  The auroral arc may stretch thousands of kilometers across North America at this point in time.  The arc may measure several hundred meters high but only 1 km or so in width.  The swirling shape is the result of the auroral arc folding back on itself like a ribbon. 
The northern lights begin to brighten and a rosy glow forms on the bottom of the arc.  This is caused by very energetic particles entering low in the atmosphere (80 km - 100 km) and causing Nitrogen molecules to emit a broad band of light in the red spectral region. 
 
The aurora is waning - quieting down for perhaps the rest of the night or perhaps to flare to brilliance again in a few minutes.  This is just part of the surprise and fascination of northern lights!