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aurora A luminous phenomenon due to electrical discharges in the atmosphere, confined to the very thin air high above the surface of the earth at some 80 to 100 km. It is most commonly seen in high latitudes where it is most frequent during periods of greatest sunspot activity. If it occurs in the Northern Hemisphere, it is called aurora borealis or northern lights; and if in the Southern, aurora australis. Charged particles emitted from the sun (solar wind) generate light wherever they enter the atmosphere by colliding with atoms and exciting the electrons of the atoms, which in turn emit light as they de-excite. This is the same process that occurs when light is emitted from a florescent or neon light. We see the aurora almost exclusively centered about the magnetic poles (auroral zone), however, because the magnetic fields in those regions trap the incoming particles into spirals, which very greatly increases their path length through the atmosphere. The longer path length gives them a much greater opportunity to interact with atoms of the air and consequently give off enough light for us to detect by naked eye.

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