The earth isn't at night or dark at all altitudes at the same time. It might be night on the ground but high up it might still be day. This is exactly what happens at sunset. During sunset when the sun goes below the horizon, the ground becomes dark but clouds high up can still receive sunlight and gives a golden shine. A certain type of unusual cloud called Noctilucent clouds form so high up in the atmosphere (about 75Km to 85Km) that they can be seen well after dark. They are the highest clouds in the Earth's atmosphere, normally too faint to be seen and are visible only when illuminated by sunlight.
Not much is know about this phenomenon also known as polar mesospheric clouds. Recent studies have shown that at least some noctilucent clouds are formed when exhausts from space shuttle, which consist primarily of water vapor, condenses at high altitudes. The following picture shows such a man made noctilucent cloud.
The following picture was taken by the Aeronomy of Ice in the Mesosphere (AIM) satellite mission which is exploring Polar Mesospheric Clouds (PMCs), or noctilucent clouds, to find out why they form and why they are changing. More information and photos on their site.
Here are two more galleries of noctilucent clouds
Noctilucent Cloud Images
Tunguska
And since you posted this, they've been seen Ben more often and in even lower latitudes in the north hemisphere... They require extremely cod temperatures to form and when first observed, were only seen over Antarctica. But not anymore...
ReplyDelete