Rare noctilucent clouds light up the sky
Last night delivered a spectacular showing of noctilucent clouds in the sky above the UK, leading to a flurry of tweets this morning, asking me what they are.
The word noctilucent comes from the Latin words nocti and lucent, meaning night and shining respectively.
The rarity of catching a glimpse of noctilucent clouds means that each summer, dedicated cloud spotters stare up at the sky, hoping to catch them on camera.
They are the highest clouds in the earth’s atmosphere, found in the mesophere – around 50 miles above the ground.
Formed from tiny ice crystals, they are characterised by their thin streaky cirrus-like appearance, and are usually bluish of silvery in colour.
The reason for them being so rare is because they occur in a part of the atmosphere that is extremely dry and has very little moisture present.
Also, there are very few cloud condensation nuclei, such as volcanic dust or debris from meteors, for water vapour to stick to – making their presence such a rare occurrence.
In addition, they are only found at latitudes of around 45 to 80 degrees north or south of the equator and require the sun to be below the horizon.
It’s the presence of the sun below the horizon that illuminates the clouds from below, meaning that they often appear faintly.
— David Whinham (@DavidWhinham) July 7, 2014
Video: Danny Spring
If you manage to spot any noctilucent clouds in the coming day and manage to capture them on camera, you can send your pictures to me on Twitter – @liamdutton