Rare night-shining clouds visible again over Czechia

A rare type of cloud known as noctilucent, or night-shining, is once again visible over Czechia and the rest of Central Europe, astronomer Petr Horálek from the Institute of Physics in Opava said on Thursday.

These clouds form unusually high in the atmosphere and are invisible during the day. They can be spotted around dusk or dawn as silvery or electric-blue veils low on the northern horizon, lit by sunlight from below the horizon.

Most commonly seen in the weeks surrounding the summer solstice, this year on June 21, they form when ice crystals cling to fine dust particles left by meteors, volcanic eruptions, or even industrial activity. Though they appear to glow, the clouds do not emit light themselves—they simply scatter sunlight from below the horizon.