Northern lights

Northern lights

Fig. 3.20 . Spectacular green curtains of light dance and shimmer across the northern sky. High-energy electrons are funneled down the Earth’s polar magnetic field lines into the atmosphere, where they excite oxygen atoms that fluoresce green light, like a cosmic neon sign. The color is usually green, but the aurora can also have red bottoms, arising from excited nitrogen molecules. This photograph of the fluorescent Northern Lights, or Aurora Borealis, was taken over Fairbanks, Alaska. (Courtesy of Jan Curtis.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University