Polar lights are a really amazing spectacle. They glow in different yellow, green, blue and red tones, sometimes they even form big bands in the sky, which slowly move around and form beautiful and dramatic shapes.
The phenomenon is limited to the northern countries such as Norway, Sweden, Finland, Iceland, Alaska, Canada and Greenland. The best time to observe Auroras is winter time between September and March. The nights are long and cold enough and the chances of a cloudless sky are high.
An aurora is sometimes referred to as a polar lights or northern lights. It is a natural light display in the sky predominantly seen in the high latitude regions. They are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma. Full explaination on wikipedia.