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Thinning Upper Atmosphere
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Thinning Upper Atmosphere

February 23, 2004
From a vantage point about 360 km (225 miles) over the Earth, Space Station crewmembers photographed the crescent moon through the upper layers of Earth’s atmosphere. At the bottom of the image, a closed deck of clouds is probably at about 6 km (3 miles). The shades of blue grading to black are caused by the scatter of light as it strikes gas molecules of the very low density upper atmosphere. Models predict that emissions of carbon dioxide are causing the upper atmosphere to cool and contract, and therefore reduce the density of gases in the layer spanning from 90 to 649 km (60 to 400 miles) above the surface—known as the thermosphere.


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