What Is The Aurora In The Sky?

The aurora in the sky is the northern or southern lights. No written description or photographs can convey the true magnificence of these ever-changing, luminous displays, often in vivid colours. Sometimes they are so bright that one can read by their light.
Generally the aurora flickers, suggesting a blazing fire just over the hill. Often the glow kindles into brilliance, assuming the shape of a huge arc, or it may take the form of bundles of rays like those of sunlight shining through holes in a cloud. These shafts of light may be pale white, emerald green, violet or rose red. At times the aurora may appear to hang in folds like a huge curtain or drapery of a stage. It may shimmer like the folds of a great screen hanging from the sky that is stirred by a silent wind. Or it may burst into feverish activity. Yellow becomes tinged with red and green as rays leap upward, subside, then dart ahead again.
There is nothing with which one can compare the delicate beauty and colouring of the aurora caused by clouds of electrically charged particles coming from the sun and entering the earth's magnetic field. These particles collide with molecules of air, causing them to vibrate and give off the red, white, blue and green lights of their awesome displays.

Scientifically... Electrically charged particles from a solar flare colliding with superheated ions in the magnetosphere and upper thermosphere