In Greek mythology, Iris was the goddess of rainbows and the messenger of the gods. She also serves as the etymological basis for the term iridescence, used for the subtle colours that can occur as sunlight shines through thin clouds.

This iridescence appeared over Lancashire, England as the sky cleared after a morning of showers. It formed in Cirrocumulus clouds spotted by Craig Loftus (Member 52,378). These were a lace-like pattern known as lacunosus, which means ‘having holes or furrows’ in Latin. The reason the subtle colours appeared as the light shone through the fringes of cloud related to the size of its droplets. These would have been tiny supercooled water droplets, likely at the point of changing into ice crystals. Being particularly small and consistent in size, these droplets had scattering effects on the sunlight that combined to separate the light into its constituent hues.

Either that, or Iris was sending down a quick apology for the showers of the morning just passed.