Figure 9-20: The Aurora An increased flow of charged particles from the Sun can overload the Van Allen belts and cascade toward Earth, producing aurorae. (a) This false-color ultraviolet image from the Dynamics Explorer 1 spacecraft shows a glowing oval of auroral emission about 4500 km in diameter centered on the north magnetic pole. (b) This photograph shows the aurora australis over Antarctica as seen from NASA’s IMAGE satellite. (c) This view from Alaska shows aurorae at their typical altitudes of 100 to 400 km. The green color shows that the light is emitted by excited oxygen atoms in the upper atmosphere.

(a: Courtesy of L. A. Frank and J. D. Craven, University of Iowa; b: NASA; c: J. Finch/Photo Researchers, Inc.)