If Iris, the goddess of the rainbow, had a sister she would be the goddess of Aurora.

Glowing green ripples form arcs that constantly transform their shape into new glowing diaphanous forms: there is nothing static about aurora. It is always moving, always changing, and like snowflakes, each display is different from the last. Sometimes, there is a faint touch of red layered above the green. There are bright spots within the arcs that come and go, and transform into upward directed rays topped by feathery red structures. Sometimes there will be six or more rays, sometimes none at all.

-Don Pettit, February, 2, 2004 -  http://earthobservatory.nasa.gov/Study/ISSAurora/iss_aurora.html

I'm truly sorry for all the cutting and pasting but I'm not suppsed to be typing at all, sigh... enjoy the above while I recover....