Noctilucent clouds are delicate, silvery-blueish clouds far above the troposphere. In summer time, they exist at about 82 km high (50 miles), high enough for the sunlight to illuminate them during the night. They can make a fantastic view, as I myself found out while taking my first photo series in the night of 18 to 19 June 1999. Note the beautiful sea of surface-fog draped like a veil over the countryland.
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