Noctilucent clouds are tenuous cloud-like phenomena in the upper atmosphere. They are made of ice crystals and are only visible in a deep twilight. Noctilucent roughly means ‘night shining’ in Latin. They are most commonly observed in the summer months at latitudes between 50° and 70° north and south of the equator.
These clouds can be observed only during local summer months and when the Sun is below the horizon for the observer, but while the clouds are still in sunlight.
While they are usually a purely natural phenomenon, the photo above shows noctilucent cloud over Orlando, Florida, formed by the frozen condensation trails of a rocket launch about 90 minutes earlier.
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