Nacreous clouds look like kites decorated with iridescent hues. They fly right up in the stratosphere, at altitudes of 9 to 16 miles (15 to 25 kilometres) – far higher than most cloud formations. The ice crystals in these rare extreme-altitude formations bend the sunlight passing around them, separating it into delicate ribbons of colour. This is why they’re also known as mother-of-pearl clouds. Air up in the stratosphere is quite dry, and so the cloud’s tiny ice crystals can form only when temperatures dip below −85ºC (−120ºF). This is something that only happens in the months around mid-winter. Nacreous cloudspottings peak in the months of December and January in the Northern Hemisphere and June and July in the Southern. The requisite cold temperatures also mean that these clouds are mostly restricted to higher latitudes. Classic locations for nacreous are northern Canada, Scandinavia, and Antarctica.

If you’re in the right region at the right time of year, look for the pastel streamers of nacreous during the hour just before sunrise or just after sunset, when the Sun shines from below the horizon, and the rest of the sky is dim. Things were just so when app user ‘Maren’ spotted these fluttering in the icy winds over Skei, Vestland, Norway.