The beautiful blaze of the Northern Lights, or Aurora Borealis, is caused when material thrown off the surface of the sun collides with the atmosphere of the Earth. Think of the sun as the father of the northern lights. It gives off high-energy charged particles that travel out into space.
A cloud of such particles is called plasma. The stream of plasma coming from the sun is known as the solar wind. As the solar wind interacts with the edge of the earth's magnetic field, some of the particles are trapped by it and they follow the lines of magnetic force down into the ionosphere, the section of the earth's atmosphere that extends from about 60 to 600 kilometers above the earth's surface.
When the particles collide with the gases in the ionosphere they start to glow, producing the spectacle that we know as the auroras, in the northern skies: the Northern Lights or Aurora Borealis and in the southern skies: Aurora Australis. The array of colors consists of red, green, blue and violet. The aurora has a curtain-like shape; the altitude of its lower edges can reach to upwards of sixty miles.
The Northern Lights are constantly in motion because of the changing interaction between the solar wind and the earth's magnetic field. In the northern hemisphere they extend over northern Scandinavia, the whole of Canada, northern USA, Alaska and Siberia. In the case of Alaska, the Earth's rotational axis means the best time for viewing the Northern Lights is late at night until the early morning hours from 10PM until 3AM.
On the other hand, it is always worth keeping in mind that a solar storm can appear at any time of the day or night, and hunters of spectacular shows would therefore be well advised to concentrate on following the various types of forecasts and predictions which are published on the Internet.