It is impossible to have a day without clouds on Earth because clouds are a natural part of the atmosphere. Clouds form when water vapour in the air condenses into small water droplets or ice crystals. These droplets and crystals then collide and stick together to form larger clouds. The amount and type of cloud cover that occurs on any given day depends on a variety of factors, including the temperature and humidity of the air, the amount of solar radiation, and the presence of air pollution.