Astronaut Luca Parmitano captured from ISS mesospheric clouds.

Credit: Luca Parmitano, ESA, NASA

Noctilucent clouds, or Polar Mesospheric Clouds (PMC), or night shining clouds, are tenuous cloud-like phenomena in the upper atmosphere of Earth. They consist of ice crystals and are only visible during astronomical twilight. They are most often observed during the summer months at high-altitude areas. They are the highest clouds in Earth’s atmosphere, located in the mesosphere at altitudes of around 75-85km. They are too faint to be seen in daylight, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in Earth’s shadow.

Reference: Luca Parmitano’s Tweet
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