Auroral Picture from the Space Shuttle

The aurora occurs in tall curtain-like structures. The bottom end of these curtains tends to be green (the image has a somewhat off-color tint towards the blue), while the upper end is dominated by red atomic oxygen emissions. The greenish thin bright line that appears to be parallel to the limb of the Earth on the left side of the image is the airglow layer, which is due to chemical reactions in the ionosphere.