Noctilucent clouds are the highest clouds in Earth's
atmosphere, forming in the mesosphere about 76 to 85 kilometers (50 miles)
above the surface.
Meaning "night-shining" in Latin, they appear as
electric-blue, silvery, or glowing wisps during summer deep twilight when they
are illuminated by the sun from below the horizon.
Noctilucent clouds (NLCs), also called polar mesospheric
clouds (PMCs) when viewed from space, are a tenuous atmospheric phenomenon.
Unlike typical weather clouds that form less than 12 miles above Earth, NLCs
occur at the very edge of space.How
For noctilucent clouds to form, three precise ingredients
are required:
Extremely Low Temperatures: Temperatures in the mesosphere
must drop below -120°C to -140°C.Water
Trace amounts of water vapor must be present.
Tiny dust particles are needed, primarily from micrometeors
burning up in the atmosphere.
Water vapor freezes onto the meteoric dust to form
microscopic ice crystals, which reflect sunlight. Their striking blue color is
a result of the ice crystals scattering sunlight in the upper atmosphere.
Noctilucent clouds are a seasonal and latitudinal
phenomenon. They occur only during the summer months when the upper atmosphere
above the polar regions experiences its coldest temperatures.
Northern Hemisphere: Best viewed between mid-May and
mid-August, primarily at mid-to-high latitudes (roughly 45° to 80° North,
including northern Europe, Canada, and the northern United States).
Southern Hemisphere: Best viewed between mid-November and
mid-February
Photos taken in Vallentuna Sweden 16-17/7 2026.
