Composite image of Aurora borealis, also known as the Northern Lights in the northern hemisphere, over an illuminated home and forest. Aurorae are caused by the interaction between energetic charged particles from the Sun and gas molecules in the upper atmosphere (about 100 kilometers up). A stream of charged particles, called the solar wind, flows out into space continuously from the Sun at speeds of 400-500 kilometers per second. On reaching Earth the charged particles are drawn by Earth's magnetic field to the poles, where they collide with gas molecules in the upper atmosphere. The color produced by the effect depends upon the particles' energy. Early eskimos believed these lights were the playful souls of children on their way to heaven.