Aurora Borealis

Aurora Borealis, or Northern Lights, a luminous phenomenon seen in the polar skies. The general appearance is that of a greenish-white arc of light, varying in thickness, symmetrical about the magnetic axis of the earth, so that the highest point of the aurora is in the direction of the magnetic north. Within the arc the sky is of a deeper hue than it is outside. It is never at rest; occasionally ribbons of variegated light shoot out radially from the bow, and produce very beautiful effects. The aurora may remain visible for several hours. Observations seem to show that simultaneous appearances occur at the two poles, north and south. The probable explanation of the phenomenon is that it is an electric discharge through the atmosphere, accompanying a magnetic disturbance. This theory is countenanced by the fact that artificial aurorae working on this principle have been produced by physicists.