Noctilucent clouds
BEST TIME TO SEE: All month
The month of July represents the second half of the UK’s noctilucent cloud (NLC) season. This normally runs from late May to early August with the best chance of seeing a display during June and July.
NLCs are the highest clouds in the atmosphere, occurring in a layer 82km up in the mesosphere. At this height they are still illuminated when the Sun is between 6° and 16° below the horizon. Despite it being night for us on the ground, NLCs appear to shine against the deep twilight sky in which they sit, hence the name noctilucent which means night-shining.
If present they will normally appear low above the northwest horizon 90–120 minutes after sunset or a similar time before sunrise above the northeast horizon. An extensive display may first appear in the northwest, tracking through north before it disappears in the northeast before dawn. What’s happening here is essentially the ice sheets which are NLCs reflect sunlight, tracking the position of the Sun below the northern horizon.
NLCs may vary in appearance and in terms of how extensive they appear. A typical display will appear to shine with an electric blue colour and exhibit a delicate, mesh-like structure.
If any normal clouds are in same area, they will typically appear dark against the higher, sunlit NLCs.