Painting the high levels of the troposphere and cruising carelessly between 18,000-40,000 ft, are the wispy cirrus clouds. Due to the sub-zero temperatures at this height, they’re made up entirely of ice crystals. As the crystals fall to Earth, they’re whipped up by 150mph winds, resulting in their recognisable swooshes or ‘fall streaks.’ Luke Howard, who named the cirrus, described them as ‘pencilled on to the sky.’
When positioned correctly, their hexagonal ice crystals can refract the sunlight to create countless optical phenomena. One of these shown above is the circumzenithal arc - an upside down rainbow smiling down from the skies.