Clouds are formed from the evaporation of the oceans' water that is warmed by the Sun and rises high into the atmosphere, condensing in tiny droplets on minute particles of dust.

These occur in cirrus or cirrostratus clouds, which are often composed of ice crystals and super-cooled water droplets - water that is below freezing temperature, but still in liquid form.

Like all clouds, it forms when the air reaches its dew point, which is the temperature to which an air mass must be cooled for the water vapor in it to condense into liquid droplets.