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Aurora Australis
IMAGE: Aurora Australis
This image of the southern lights, or aurora australis, was taken in October 2001 by an Expedition Three crewmember.
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Don Pettit Space Chronicles

Expedition Six
Space Chronicles #1

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By: ISS Science Officer Don Pettit

Observing the Atmosphere

The atmosphere on edge presents a striking sight. You see many distinct layers all a different shade of iridescent blue. Through binoculars, I have counted six. I find it odd that a steady continuum of gas that decreases its density in a predictable manner displays such distinct visual layering. Below the blue you see an orange-red layer with cloud tops from rising thunderheads. These thunderheads are poking their noses up into the outer reaches of the meteoric zone where weather as we know it ends and the stratosphere begins. These cloud tops are at about 10 km (35,000 feet). If I use this for a ruler, to the eye, the "blue layers" are about 3 to 4 times this thickness. The visible part of the atmosphere then, including the lower meteoric zone, is 4 to 5 of these rulers or 40 to 50 km thick. The outer most blue layer quickly fades from a narrow fuzzy zone into blackness. The most amazing aspect of this view is how thin this life-preserving blanket is when compared to the full extent of the planet. Like an orbital eggshell, our atmosphere looks so frail that it might crack and be gone in an instant rendering Earthas barren and lifeless as any other baked hunk of rock orbiting the sun.

Curator: Kim Dismukes | Responsible NASA Official: John Ira Petty | Updated: 05/14/2003
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