A few days ago, we got treated to something very special by the weather gods. Above Reykjavík, the most colourful of clouds appeared: polar stratospheric clouds or glitský as it's called in Icelandic. These iridescent clouds are very rarely seen and only appear under very specific circumstances. They are hanging in the stratosphere, between 15 and 25 kilometres above the Earth's surface, where clouds are rarely formed. The colours are created by the rising sun's light diffracting in ice crystals within these clouds. Because of their height, the sunlight that illuminates them is coming from below the horizon.