What are noctilucent clouds?
- Published
A clear summer night sky can reveal an extraordinary natural phenomenon.
Noctilucent clouds are rare formations that can appear at twilight during the summer months.
Noctilucent clouds reflected in a car window in Paisley, Renfrewshire
The wispy, often wavy, streaks of cloud usually look silvery-blue but they can also appear red or green.
Noctilucent clouds glisten above the New Brighton Lighthouse, Wallasey
Noctilucent clouds are the highest clouds in the atmosphere, floating 50 miles (80km) above Earth in the mesosphere. This is about 10 times higher than the troposphere, where other weather clouds form.
They are made of tiny ice crystals, formed from meteor dust particles and water vapour in extremely cold temperatures of around -130C.
A bright display at Tyne Bridge in Newcastle
The high altitude of noctilucent clouds allows them to catch the sun's rays during the brief hours of midsummer darkness, when the sun is well below the local horizon. Normal weather clouds lie in deep shadow during this time.
A noctilucent filled sky in Derbyshire
Look for the ethereal formations an hour after sunset or an hour before sunrise.
Noctilucent clouds can be seen with the naked eye so if you spot them don't forget to share your photos with 大象传媒 Weather Watchers.