When conditions are right and people are in the right spot it is sometimes possible to see what is called an airglow. About 90 kilometers above the Earth's surface a faint glow is visible, seen frequently when pictures are taken from space. There can be many different colors, green however, was the color featured the other day. The glow comes from the excitation of ultraviolet rays, excited by the Sun and then emitting colors. They are excited when the bands fluctuate due to the atmospheric gravity waves. This can happen around the world and although it is easier to see with a camera or telescope most can still view the phenomenon with their naked eye.
http://apod.nasa.gov/apod/image/1209/airglow_hackmann_1400.jpg
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