Aurora frequently make complete rings around
a pole of the Earth. This particular "crown",
visible in orange near the top of this image,
was taken by the orbiting Polar spacecraft
about one year ago and released by NASA last month. A complete
auroral
oval is normally hard to photograph because part of it usually
occurs over a brightly sunlit portion of the Earth. Polar's
Earth Camera,
however, can be programmed to filter out all but a certain type
of ultraviolet light. In this
"color", atmospheric oxygen
can glow brighter than reflected sunlight. People with normal
eyesight living near the Great Lakes
in North America would have been able to see this aurora,
were it not daytime!
