NASA Maps Night-shining Clouds
This image of noctilucent clouds was taken by the Aeronomy of Ice in the Mesosphere (AIM) satellite on July 14, 2009. The North Pole is in the center. Latitude bands of 80N, 70N, and 60N are also indicated by the light blue circles.
Credit: NASA

A NASA satellite has created a new map of so-called "night-shining clouds," which form at high altitudes on Earth and glow even after the sun sets.

These mysterious clouds, also called noctilucent clouds or Polar Mesospheric Clouds (PMCs), appear about 50 miles (80 km) above Earth's surface during the summer of each hemisphere ? from late May through late August in the north, and from late November to late February in the south.

NASA's Aeronomy of Ice in the Mesosphere (AIM) satellite has captured five complete polar seasons of noctilucent cloud coverage, showing that they can quickly form and disperse, and that they are highly dependent on weather systems.

"The AIM findings have altered our previous understanding of why PMCs form and vary," said AIM principal investigator James Russell III of Hampton University in Virginia. "We have captured the brightest clouds ever observed and they display large variations in size and structure signifying a great sensitivity to the environment in which the clouds form."

Noctilucent clouds are made of ice crystals that form when water vapor condenses onto dust particles at the extremely frigid temperatures at high altitudes, between minus 210 to minus 235 degrees Fahrenheit (minus 134 to -148 degrees Celsius).

They are visible even when the sky is dark because that high up, the clouds can continue to reflect sunlight after the sun has set below the horizon. Their spectacular silvery-blue display can be seen well into the night.

The AIM results show that the atmospheric temperature seems to determine when the season for night-shining clouds begins and how long it lasts.

"The cloud season abruptly turns on and off going from no clouds to near complete coverage in a matter of days with the reverse pattern occurring at the season end," Russell said.

AIM was launched in 2007 on a dedicated mission to study noctilucent clouds and learn more about how and why they form, and why they appear to be occurring at lower latitudes than ever before.