Asked by Fern Berger
Noctilucent clouds (NLCs) tend to look like delicate streaky clouds, which can only be seen in the twilight hours between May and August. They are the highest clouds we know of at around 80 kilometres (50 miles) up in the mesosphere layer of our atmosphere.
Water vapour and dust particles are needed for an NLC to form, but both are fairly sparse at that high altitude.
It’s thought that a supply of dust may come from micrometeors or from volcanic eruptions, while water vapour may have been lifted up through the lower atmospheric layers or created by chemical reactions. Together these two components form tiny ice crystals, which are the primary components of an NLC. Cold levels are needed for ice crystals to form and at a chilly -123 degrees Celsius (-184 Fahrenheit).
Answered by Zoe Baily from the National Space Centre
Image Credit: Martin Koitmäe
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