The basic form of an aurora usually resembles a long curtain, the bottom edge of which ends about 55 miles above the Earth. When viewed from many miles south of where it's displaying, it will often have a bottom edge that follows something close to a straight line. If you're located even farther south, it will often appear as a just misty green glow on the horizon. But when viewed from directly below, it takes on a dramatically different appearance. The folds in an active auroral curtain can become quite prominent, and what are actually parallel rays appear to converge at a point (the "zenith") hundreds of miles above. This is perspective at work-- the same effect experienced when one stands on a long, straight stretch of train track and the rails appear to converge in the distance. This beautiful corona was captured while it hovered above central Alaska.
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